[DOCKET NO. 121973]
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`LOW NOISE AMPLIFIERS FOR CARRIER AGGREGATION
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`§119I. Claim of Priority under 35 U.S.C.
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`[0001] The present Application for Patent claims priority to Provisional U.S.
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`Application Serial No. 61/652,064, entitled "LOW NOISE AMPLIFIERS FOR
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`CARRIER AGGREGATION," filed May 25, 2012, assigned to the assignee hereof, and
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`expressly incorporated herein by reference.
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`I. Field
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`BACKGROUND
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`[0002] The present disclosure relates generally to electronics, and more specifically to
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`low noise amplifiers (LNAs ).
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`II.Background
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`[0003]
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`A wireless device ( e.g., a cellular phone or a sma1iphone) in a wireless
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`communication system may transmit and receive data for two-way communication. The
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`wireless device may include a transmitter for data transmission and a receiver for data
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`reception. For data transmission, the transmitter may modulate a radio frequency (RF)
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`carrier signal with data to obtain a modulated RF signal, amplify the modulated RF
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`signal to obtain an amplified RF signal having the proper output power level, and
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`transmit the amplified RF signal via an antenna to a base station. For data reception, the
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`receiver may obtain a received RF signal via the antenna and may amplify and process
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`the received RF signal to recover data sent by the base station.
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`[0004] A wireless device may support carrier aggregation, which is simultaneous
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`operation on multiple carriers. A carrier may refer to a range of frequencies used for
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`communication and may be associated with certain characteristics. For example, a
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`carrier may be associated with system information describing operation on the carrier.
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`A carrier may also be referred to as a component carrier (CC), a frequency channel, a
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`cell, etc. It is desirable to efficiently support carrier aggregation by the wireless device.
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`INTEL 1011
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`[DOCKET NO. 121973]
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG.
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`1 shows a wireless device communicating with a wireless system.
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`FIGS. 2A to 2D show four examples of carrier aggregation (CA).
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`FIG. 3 shows a block diagram of the wireless device in FIG. 1.
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`FIGS. 4A and 4B show a receiver supporting intra-band CA.
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`FIGS. 5A and 5B show a receiver supporting intra—band CA and inter-band CA.
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`FIGS. 6A to 6C show an LNA with inductive degeneration and cascode shutoff.
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`FIG. 7 shows an LNA with inductive degeneration, cascode shutoff, and
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`resistive feedback.
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`FIG. 8A shows an LNA with a separate input attenuation circuit for each
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`amplifier stage.
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`FIG. 8B shows an LNA with a shared input attenuation circuit for two amplifier
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`stages.
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`FIG. 9 shows an LNA with a tunable input matching circuit.
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`FIGS. 10 to 11C show several exemplary designs of a multiple-input multiple—
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`Output (MIMO) LNA.
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`FIGS. 12A to 12F show six exemplary designs of a tunable input matching
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`circuit.
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`FIG. 13 shows a process for receiving signals in a wireless system.
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`[0005]
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`[0006]
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`[0007]
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`[0008]
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`[0009]
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`[0010]
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`[0011]
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`[0012]
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`[0013]
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`[0014]
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`[0015]
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`[0016]
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`[0017]
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`[0018]
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`The detailed description set
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`forth below is
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`intended as a description of
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`DETAILED DESCRIPTION
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`exemplary designs of the present disclosure and is not intended to represent the only
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`designs in which the present disclosure can be practiced. The term “exemplary” is used
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`herein to mean “serving as an example, instance, or illustration.” Any design described
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`herein as “exemplary” is not necessarily to be construed as preferred or advantageous
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`over other designs. The detailed description includes specific details for the purpose of
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`providing a thorough understanding of the exemplary designs of the present disclosure.
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`It will be apparent to those skilled in the art that the exemplary designs described herein
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`may be practiced without
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`these specific details.
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`In some instances, well—known
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`structures and devices are shown in block diagram form in ordcr to avoid obscuring the
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`novelty of the exemplary designs presented herein.
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`[DOCKET NO. 121973]
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`3
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`[0019]
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`LNAs supporting carrier aggregation are disclosed herein. These LNAs may
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`have better performance and may be used for various types of electronic devices such as
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`wireless communication devices.
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`[0020]
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`FIG.
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`1
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`shows
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`a wireless device
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`110 communicating with a wireless
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`communication system 120. Wireless system 120 may be a Long Term Evolution
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`(LTE) system, a Code Division Multiple Access (CDMA) system, a Global System for
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`Mobile Communications (GSM) system, a wireless local area network (WLAN) system,
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`or some other wireless system. A CDMA system may implement Wideband CDMA
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`(WCDMA), cdma2000, or some other version of CDMA. For simplicity, FIG. 1 shows
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`wireless system 120 including two base stations 130 and 132 and one system controller
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`140.
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`In general, a wireless system may include any number of base stations and any set
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`of network entities.
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`[0021]
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`Wireless device 110 may also be referred to as a user equipment (UE), a mobile
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`station, a terminal, an access terminal, a subscriber unit, a station, etc. Wireless device
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`110 may be a cellular phone, a smartphone, a tablet, a wireless modem, a personal
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`digital assistant (PDA), a handheld device, a laptop computer, a smartbook, a netbook, a
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`cordless phone, a wireless local loop (WLL) station, a Bluetooth device, etc. Wireless
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`device 110 may be capable of communicating with wireless system 120. Wireless
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`device 110 may also be capable of receiving signals from broadcast stations (e.g., a
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`broadcast station 134), signals from satellites (e.g., a satellite 150) in one or more global
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`navigation satellite systems (GNSS), etc. Wireless device 110 may support one or more
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`radio technologies for wireless communication such as LTE, cdma2000, WCDMA,
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`GSM, 802.11, etc.
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`[0022]
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`Wireless device 110 may support carrier aggregation, which is operation on
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`multiple carriers. Carrier aggregation may also be referred to as multi—carrier operation.
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`Wireless device 110 may be able to operate in low—band from 698 to 960 megahertz
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`(MHz), mid-band from 1475 to 2170 MHz, and/or high-band from 2300 to 2690 and
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`3400 to 3800 MHz. Low-band, mid-band, and high—band refer to three groups of bands
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`(or band groups), with each band group including a number of frequency bands (or
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`simply, “bands”). Each band may cover up to 200 MHz and may include one or more
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`carriers. Each carrier may cover up to 20 MHz in LTE. LTE Release 11 supports 35
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`bands, which arc rcfcrrcd to as LTE/UMTS bands and arc listcd in 3GPP TS 36.101.
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`[DOCKET NO. 121973]
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`4
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`Wireless device 110 may be configured with up to 5 carriers in one or two bands in LTE
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`Release ll.
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`[0023]
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`In general, carrier aggregation (CA) may be categorized into two types - intra-
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`band CA and inter-band CA.
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`Intra—band CA refers to operation on multiple carriers
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`within the same band.
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`Inter-band CA refers to operation on multiple carriers in
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`different bands.
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`[0024]
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`FIG. 2A shows an example of contiguous intra—band CA. In the example shown
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`in FIG. 2A, wireless device 110 is configured with four contiguous carriers in the same
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`band. which is a band in low-band. Wireless device 110 may receive transmissions on
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`multiple contiguous carriers within the same band.
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`[0025]
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`FIG. 2B shows an example of non-contiguous intra-band CA.
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`In the example
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`shown in FIG. 2B, wireless device 110 is configured with four non—contiguous carriers
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`in the same band, which is a band in low-band. The carriers may be separated by 5
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`MHz. 10 MHz, or some other amount. Wireless device 110 may receive transmissions
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`on multiple non-contiguous carriers within the same band.
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`[0026]
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`FIG. 2C shows an example of inter-band CA in the same band group.
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`In the
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`example shown in FIG. 2C, wireless device 110 is configured with four carriers in two
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`bands in the same band group. which is low-band. Wireless device 110 may receive
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`transmissions on multiple carriers in different bands in the same band group (e. g.. low-
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`band in FIG. 2C).
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`[0027]
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`FIG. 2D shows an example of inter-band CA in different band groups.
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`In the
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`example shown in FIG. 2D, wireless device 110 is configured with four carriers in two
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`bands in different band groups, which include two carriers in one band in low—band and
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`two additional carriers in another band in mid-band. Wireless device 110 may receive
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`transmissions on multiple carriers in different bands in different band groups (e. g., low-
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`band and mid-band in FIG. 2D).
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`[0028]
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`FIGS. 2A to 2D show four examples of carrier aggregation. Carrier aggregation
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`may also be supported for other combinations of bands and band groups. For example,
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`carrier aggregation may be supported for low-band and high-band, mid-band and high-
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`band, high-band and high-band, etc.
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`[0029]
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`FIG. 3 shows a block diagram of an exemplary design of wireless device 110 in
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`FIG.
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`1.
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`In this cxcmplary dcsign, wireless device 110 includes a transceiver 320
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`coupled to a primary antenna 310, receivers 322 coupled to a secondary antenna 312,
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`[DOCKET NO. 121973]
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`5
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`and a data processor/controller 380. Transceiver 320 includes multiple (K) receivers
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`330aa to 330ak and multiple (K) transmitters 360a to 360k to support multiple bands,
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`carrier aggregation, multiple radio technologies, etc. Receivers 322 include multiple
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`(M) receivers 330ba to 330bm to support multiple bands, carrier aggregation, multiple
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`radio technologies, receive diversity, MIMO transmission, etc.
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`[0030]
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`In the exemplary design shown in FIG. 3, each receiver 330 includes input
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`circuits 332, an LNA 340, and receive circuits 342. For data reception, antenna 310
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`receives signals from base stations and/or other transmitter stations and provides a
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`received RF signal, which is routed through switches/duplexers 324 and provided to a
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`selected receiver. The description below assumes that receiver 330aa is the selected
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`receiver. Within receiver 330aa, the received RF signal is passed through input circuits
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`332aa, which provides an input RF signal to an LNA 340aa.
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`Input circuits 332aa may
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`include a matching circuit, a receive filter, etc. LNA 340aa amplifies the input RF
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`signal and provides an output RF signal. Receive circuits 342aa amplify, filter, and
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`downconvert the output RF signal from RF to baseband and provide an analog input
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`signal to data processor 380. Receive circuits 332aa may include mixers, a filter, an
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`amplifier, a matching circuit, an oscillator, a local oscillator (LO) generator, a phase
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`locked loop (PLL), etc. Each remaining receiver 330 in transceiver 320 and each
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`receiver 330 in receivers 322 may operate in similar manner as receiver 330aa in
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`transceiver 3 20.
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`[0031]
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`In the exemplary design shown in FIG. 3, each transmitter 360 includes transmit
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`circuits 362, a power amplifier
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`(PA) 364, and output circuits 366.
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`For data
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`transmission, data processor 380 processes (e.g., encodes and modulates) data to be
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`transmitted and provides an analog output signal
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`to a selected transmitter.
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`The
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`description below assumes that transmitter 360a is the selected transmitter. Within
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`transmitter 360a, transmit circuits 362a amplify, filter, and upconvert the analog output
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`signal from baseband to RF and provide a modulated RF signal. Transmit circuits 362a
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`may include mixers, an amplifier, a filter, a matching circuit, an oscillator, an L0
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`generator, a PLL, etc. A PA 364a receives and amplifies the modulated RF signal and
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`provides an amplified RF signal having the proper output power level. The amplified
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`RF signal is passed through output circuits 366a, routed through switches/duplexers
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`324, and transmitted via antenna 310. Output circuits 366a may include a matching
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`circuit, a transmit filter, a directional coupler, etc.
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`[DOCKET NO. 121973]
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`6
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`[0032]
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`FIG. 3 shows an exemplary design of receivers 330 and transmitters 360. A
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`receiver and a transmitter may also include other circuits not shown in FIG. 3, such as
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`filters, matching circuits, etc. All or a portion of transceiver 320 and receivers 322 may
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`be implemented on one or more analog integrated circuits (ICs), RF ICs (RFICS),
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`mixed—signal ICs, etc. For example, LNAs 340, receive circuits 342, and transmit
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`circuits 362 may be implemented on one module, which may be an RFIC, etc.
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`Switches/duplexers 324, switches/filters 326, input circuits 332, output circuits 366, and
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`PAs 364 may be implemented on another module, which may be a hybrid module, etc.
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`The circuits in receivers 330 and transmitters 360 may also be implemented in other
`manners.
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`[0033]
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`Data processor/controller 380 may perform various functions for wireless device
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`110. For example, data processor 380 may perform processing for data being received
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`via receivers 330 and data being transmitted via transmitters 360. Controller 380 may
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`control the operation of switches/duplexers 324, switches/filters 326, input circuits 332,
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`LNAs 340, receive circuits 342, transmit circuits 362, PAs 364, output circuits 366, or a
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`combination thereof. A memory 382 may store program codes and data for data
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`processor/controller 380. Data processor/controller 380 may be implemented on one or
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`more application specific integrated circuits (ASICs) and/or other ICs.
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`[0034]
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`Wireless device 110 may receive multiple transmissions from one or more
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`cells/base stations on multiple carriers at different frequencies for carrier aggregation.
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`For intra-band CA, the multiple transmissions are sent on multiple carriers in the same
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`band. For inter-band CA, the multiple transmissions are sent on multiple carriers in
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`different bands.
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`[0035]
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`FIG. 4A shows a block diagram of an exemplary design of a receiver 400 that
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`includes a CA LNA 440 supporting no CA and intra—band CA. CA LNA 440 may be
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`used for one or more LNAs 340 within wireless device 110 in FIG. 3.
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`[0036]
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`At receiver 400, an antenna 410 receives transmissions on multiple carriers in
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`the same band and provides a received RF signal. The received RF signal is routed
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`through switches/duplexers 424 and provided as a receiver input signal, RXin, to an
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`input matching circuit 432. Matching circuit 432 performs power and/or impedance
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`matching between CA LNA 440 and either switches/duplexers 424 or antenna 410 for
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`one or more bands of interest. Matching circuit 432, which may be part of one of input
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`circuits 332 in FIG. 3, provides an input RF signal, RFin, to CA LNA 440.
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`[DOCKET NO. 121973]
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`7
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`[0037]
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`CA LNA 440 receives the input RF signal from matching circuit 432, amplifies
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`the input RF signal, and provides up to M output RF signals, RFoutl to RFoutM, via up
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`to M LNA outputs, where M >1. M load circuits 490a to 490m are coupled to the M
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`LNA outputs. Each load circuit 490 may include one or more inductors, capacitors,
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`transistors, mixers, etc. Each load circuit 490 may be part of one of receive circuits 342
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`in FIG. 3. Each output RF signal may be provided to one or more mixers within one
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`load circuit 490 and may be downconverted by the associated mixer(s) such that
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`transmissions on one or more carriers of interest are downconverted from RF to
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`baseband.
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`[0038]
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`A CA LNA, such as CA LNA 440 in FIG. 4A, may operate in a non-CA mode
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`or a CA mode at any given moment.
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`In the non-CA mode, the CA LNA operates in a 1-
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`input
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`l-output (lxl) configuration, receives one input RF signal comprising one or
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`more transmissions on one set of carriers, and provides one output RF signal to one load
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`circuit.
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`In the CA mode, the CA LNA operates in a 1x M configuration, receives one
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`input RF signal comprising multiple transmissions on M sets of carriers, and provides M
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`output RF signals to M load circuits, one output RF signal for each set of carriers, where
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`M > 1. Each set of carriers may include one or more carriers in one band.
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`[0039]
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`FIG. 4B shows a schematic diagram of an exemplary design of a CA LNA 440x
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`supporting no CA and intra-band CA on two sets of carriers in the same band. CA LNA
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`440x is one exemplary design of CA LNA 440 in FIG. 4A.
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`In the exemplary design
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`shown in FIG. 4B, CA LNA 440x receives an input RF signal from input matching
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`circuit 432 and provides up to two output RF signals, RFoutl and RFout2, for up to two
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`sets of carriers. The first output RF signal is provided to a load circuit 490x, and the
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`second output RF signal is provided to a load circuit 490y.
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`[0040]
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`In the exemplary design shown in FIG. 4B,
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`load circuit 490x includes two
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`mixers 492a and 492b coupled to two baseband filters 494a and 494b, respectively.
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`Mixers 492a and 492b implement a quadrature downconverter for a first set of carriers.
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`Mixer 492a receives the first output RF signal from CA LNA 440x and an inphase LO
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`signal, ILOl, at a first mixing frequency for the first set of carriers. Mixer 492a
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`downconverts the first output RF signal with the ILOl signal and provides an inphase
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`(I) downconverted signal. Mixer 492b receives the first output RF signal from CA LNA
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`440x and a quadrature LO signal, QLOl, at thc first mixing frcqucncy for the first sct of
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`carriers. Mixer 492b downconverts the first output RF signal with the QLOl signal and
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`[DOCKET NO. 121973]
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`8
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`provides a quadrature (Q) downconveited signal. Filters 494a and 494b receive and
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`filter the I and Q downconveited signals from mixers 492a and 492b, respectively, and
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`provide I and Q baseband signals, Voutl, for the first set of carriers.
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`[0041]
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`Mixers 492c and 492d and filters 494c and 494d within load circuit 490y
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`similarly process the second output RF signal from CA LNA 440x and provide I and Q
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`baseband signals for a second set of carriers. Mixers 492c and 492d receive the second
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`RF signal and I and Q LO signals, respectively, at a second mixing frequency for the
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`second set of carriers. Mixers 492c and 492d downconvert the second output RF signal
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`with the I and Q LO signals and provide the I and Q downconveited signals,
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`respectively. Filters 494C and 494d receive and filter the I and Q downconverted
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`signals from mixers 492C and 492d, respectively, and provide I and Q baseband signals,
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`Vout2, for the second set of carriers.
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`[0042]
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`FIG. 4B shows an exemplary design of load circuits 490x and 490y. A load
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`circuit may also comprise different and/or additional circuits. For example, a load
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`circuit may include an amplifier coupled before the mixers, or between the mixers and
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`the filters, or after the filters.
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`[0043]
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`FIG. 5A shows a block diagram of an exemplary design of a receiver 500 that
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`includes a MIMO LNA 540 supporting no CA,
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`intra—band CA, and inter-band CA.
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`MIMO LNA 540 may be used for one or more LNAs 340 within wireless device 110 in
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`FIG. 3.
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`[0044]
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`At receiver 500, an antenna 510 receives transmissions on one or more carriers
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`in the same band or different bands and provides a received RF signal to switches/
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`duplexers 524. Switches/duplexers 524 provide up to N receiver input signals, RXinl
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`to RXinN, to up to N input matching circuits 532a to 532n, respectively, where N >1.
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`Matching circuits 53 2a to 53 2n may be part of one or more input circuits 332 in FIG. 3.
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`Each matching circuit 532 performs power and/or impedance matching between MIMO
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`LNA 540 and either switches/duplexers 524 or antenna 510 for one or more bands of
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`interest. The N matching circuits 5 32a to 532n may be designed for different bands and
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`may provide up to N input RF signals, RFinl to RFinN.
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`[0045]
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`MIMO LNA 540 receives up to N input RF signals and amplifies (i) one input
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`RF signal for no CA or intra—band CA or (ii) multiple input RF signals for inter—band
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`CA. MIMO LNA 540 provides up to M output RF signals, RFoutl to RFoutM, via up
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`to M LNA outputs. M load circuits 590a to 590m are coupled to the M LNA outputs.
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`[DOCKET NO. 121973]
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`9
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`Each load circuit 590 may include one or more inductors, capacitors, transistors, mixers,
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`etc. Each output RF signal may be provided to one or more mixers within one load
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`Circuit 590 and may be downconverted by the associated mixer(s) such that one or more
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`transmissions on one or more carriers of interest are downconverted from RF to
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`baseband.
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`[0046]
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`A MIMO LNA, such as MIMO LNA 540 in FIG. 5A, may operate in a non-CA
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`mode, an intra-band CA mode, or an inter—band CA mode at any given moment.
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`In the
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`non-CA mode, the MIMO LNA operates in a 1x1 configuration, receives one input RF
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`signal comprising one or more transmissions on one set of carriers, and provides one
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`output RF signal to one load circuit.
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`In the intra—band CA mode, the MIMO LNA
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`operates in a l><M configuration, receives one input RF signal comprising multiple
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`transmissions on M sets of carriers in the same band, and provides M output RF signals
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`to M load circuits, one output RF signal for each set of carriers, where M >1.
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`In the
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`inter—band CA mode, the MIMO LNA operates in an N x M configuration, receives N
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`input RF signals comprising multiple transmissions on M sets of carriers in up to N
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`different bands, and provides M output RF signals to M load circuits, where M > 1 and
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`N > 1. The N input RF signals may correspond to up to N different bands.
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`[0047]
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`A MIMO LNA, such as MIMO LNA 540 in FIG. 5A, may be used to receive
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`transmissions on multiple carriers at different frequencies. A MIMO LNA may include
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`multiple outputs providing multiple output RF signals for different carriers or different
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`sets of carriers of interest. A MIMO LNA is different from LNAs used to receive a
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`MIMO transmission sent from multiple transmit antennas to multiple receive antennas.
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`An LNA for a MIMO transmission typically has (i) one input receiving one input RF
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`signal from one receive antenna and (ii) one output providing one output RF signal.
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`The multiple outputs of a MIMO LNA thus cover frequency dimension whereas the
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`outputs of LNAs used for a MIMO transmission cover spatial dimension.
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`[0048]
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`FIG. SB shows a schematic diagram of an exemplary design of a MIMO LNA
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`540x supporting no CA, intra-band CA, and inter—band CA on two sets of carriers in
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`different bands. Each set of carriers may include one or more carriers in one band.
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`MIMO LNA 540x is one exemplary design of MIMO LNA 540 in FIG. 5A. Matching
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`circuits 532a and 532b may receive (i) the same receiver input signal from one antenna
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`or (ii) different receiver input signals from one or more antennas. Hence, the RXinZ
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`[DOCKET NO. 121973]
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`10
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`signal may or may not be equal to the RXinl signal in FIG. 5B. Each matching circuit
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`532 performs power and/or impedance matching for one or more bands of interest.
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`[0049]
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`In the exemplary design shown in FIG. 5B, MIMO LNA 540x includes two
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`amplifier stages 550a and 550b for two sets of carriers. Amplifier stage 550a receives
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`and amplifies the first input RF signal from matching circuit 532a and provides a first
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`output RF signal, RFoutl, for a first set of carriers. Amplifier stage 550b receives and
`
`amplifies the second input RF signal from matching circuit 532b and provides a second
`
`output RF signal, RFout2, for a second set of carriers. Although not shown in FIG. 5B
`
`for simplicity, MIMO LNA 540x may include circuitry to route an output RF signal
`
`from each amplifier stage 550 to any one of load circuits 590x and 590y.
`
`[0050]
`
`In the exemplary design shown in FIG. 5B,
`
`load circuit 590x includes two
`
`mixers 592a and 592b coupled to two baseband filters 594a and 594b, respectively.
`
`Mixer 592a receives the first output RF signal from amplifier stage 550a and an inphase
`
`LO signal, ILOl, at a first mixing frequency for the first set of carriers. Mixer 592a
`
`downconverts the first output RF signal with the ILOl signal and provides an I
`
`downconverted signal. Mixer 592b receives the first output RF signal from amplifier
`
`stage 550b and a quadrature LO signal, QLOl, at the first mixing frequency for the first
`
`set of carriers. Mixer 592b downconverts the first output RF signal with the QLOl
`
`signal and provides a Q downconverted signal. Filters 594a and 594b receive and filter
`
`the I and Q downconverted signals from mixers 592a and 592b, respectively, and
`
`provide I and Q baseband signals, Voutl, for the first set of carriers.
`
`[0051]
`
`Mixers 592C and 592d and filters 594c and 594d within load circuit 590y
`
`similarly process the second output RF signal from amplifier stage 550b and provide I
`
`and Q baseband signals, Vout2, for a second set of carriers.
`
`[0052]
`
`CA LNA 440 in FIG. 4A may be implemented in various manners.
`
`Some
`
`exemplary designs of CA LNA 440 are described below. CA LNA 440 may also be
`
`implemented with transistors of various types. Some exemplary designs of CA LNA
`
`440 using N-channel metal oxide semiconductor (NMOS) transistors are described
`
`below.
`
`[0053]
`
`FIG. 6A shows a schematic diagram of an exemplary design of a CA LNA 640a
`
`with inductive degeneration and cascode shutoff. CA LNA 640a is one exemplary
`
`design of CA LNA 440 in FIG. 4A. CA LNA 640a includes two amplifier stages 650a
`
`and 650b coupled to a common input matching circuit 632 and to two load circuits 690a
`
`

`

`[DOCKET NO. 121973]
`
`11
`
`and 690b. Matching circuit 632 receives a receiver input signal, RXin, performs input
`
`matching for CA LNA 640a, and provides an input RF signal, RFin. Matching circuit
`
`632 may correspond to matching circuit 432 in FIG. 4A. Load circuits 690a and 690b
`
`may correspond to load circuits 490a and 490m in FIG. 4A. CA LNA 640a receives the
`
`input RF signal, which may include transmissions on two sets of carriers, with each set
`
`including one or more carriers.
`
`[0054]
`
`In the exemplary design shown in FIG. 6A, amplifier stage 650a includes a
`
`source degeneration inductor 652a, a gain transistor 654a, and a cascode transistor 656a.
`
`Gain transistor 654a and cascode transistor 656a may be implemented with NMOS
`
`transistors (as shown in FIG. 6A) or with transistors of other types. Gain transistor 654a
`
`has its gate coupled to matching circuit 632 and its source coupled to one end of
`
`inductor 652a. The other end of inductor 652a is coupled to circuit ground. Cascode
`
`transistor 656a has its source coupled to the drain of gain transistor 654a and its drain
`
`coupled to load circuit 690a. A switch 658a has its input port coupled to the gate of
`
`cascode transistor 656a, its first output port coupled to a bias voltage, Vcasc, and its
`
`second output port coupled to circuit ground. Amplifier stage 650b includes a source
`
`degeneration inductor 652b, a gain transistor 654b, a cascode transistor 656b, and a
`
`switch 658b, which are coupled in similar manner as inductor 652a, gain transistor
`
`654a, cascode transistor 656a, and switch 658a in amplifier stage 650a.
`
`[0055]
`
`For simplicity, FIG. 6A shows CA LNA 640a including two amplifier stages
`
`650a and 650b for two sets of carriers. Amplifier stages 650a and 650b may be
`
`independently enabled or disabled via switches 658a and 658b, respectively. CA LNA
`
`640a may include more than two amplifier stages 650 for more than two sets of carriers.
`
`[0056]
`
`An input RF signal may include transmissions on multiple sets of carriers in the
`
`same band and may be referred to as a carrier—aggregated RF signal. The carrier-
`
`aggregated RF signal may be downconverted using LO signals at different frequencies
`
`corresponding to the center frequencies of the multiple sets of carriers on which the
`
`transmissions are sent. The carrier-aggregated RF signal may be split at the LNA input
`
`in order to achieve good LO-LO isolation between the LO signals for the multiple sets
`
`of carriers. CA LNA 640a includes two amplifier stages 650a and 650b to amplify the
`
`carrier-aggregated RF signal and provide two output RF signals to two separate
`
`downconvertcrs in thc two load circuits 690a and 69%.
`
`

`

`[DOCKET NO. 121973]
`
`12
`
`[0057]
`
`CA LNA 640a may operate in a non-CA mode or a CA mode at any given
`
`moment.
`
`In the non-CA mode, CA LNA 640a receives transmissions on one set of
`
`carriers and provides one output RF signal to one load circuit.
`
`In the CA mode, CA
`
`LNA 640a receives transmissions on two sets of carriers and provides two output RF
`
`signals to two load circuits, one output RF signal for each set of carriers.
`
`[0058]
`
`FIG. 6B shows operation of CA LNA 640a in the CA mode.
`
`In the CA mode,
`
`both amplifier stages 650a and 650b are enabled by connecting the gate of cascode
`
`transistor 656a to the Vcasc voltage via switch 658a and coupling the gate of cascode
`
`transistor 656b to the Vcasc voltage via switch 658b. Amplifier stage 650a amplifies
`
`the input RF signal and provides the first output RF signal
`
`to load circuit 690a.
`
`Amplifier stage 650b amplifies the input RF signal and provides the second output RF
`
`signal to load circuit 690b.
`
`[0059]
`
`FIG. 6C shows operation of CA LNA 640a in the non-CA mode.
`
`In the non-
`
`CA mode, only one amplifier stage is enabled, and the other amplifier stage is disabled.
`
`In the example shown in FIG. 6C, amplifier stage 650a is enabled by connecting the
`
`gate of cascode transistor 656a to the Vcasc voltage via switch 658a, and amplifier stage
`
`650b is disabled by shorting the gate of cascode transistor 656b to circuit ground via
`
`switch 65 8b. Amplifier stage 650a amplifies the input RF signal and provides an output
`
`RF signal to load circuit 690a.
`
`[0060]
`
`In another configuration of the non-CA mode, amplifier stage 650b is enabled,
`
`and amplifier stage 650a is disabled (not shown in FIG. 6C).
`
`In this configuration,
`
`amplifier stage 650b amplifies the input RF signal and provides an output RF signal to
`
`load circuit 690b.
`
`[0061]
`
`In the exemplary design shown in FIG. 6A, separate source degeneration
`
`inductors 652a and 652b are used for amplifier stages 650a and 650b in order to reduce
`
`interaction between the two amplifier stages and to help reduce noise figure (NF)
`
`degradation. Source degeneration inductors 652a and 652b may also improve linearity
`
`of amplifier stages 650a and 650b and help input impedance matching of CA LNA
`
`640a.
`
`Inductors 652a and 652b may have the same value or different values. The
`
`values of inductors 652a and 652b may be selected (e.g., independently) based on a
`
`trade-off between voltage gain and linearity in the CA mode and the non-CA mode.
`
`[0062]
`
`As shown in FIG. 6A, a variable capacitor 668a may be present across the gate
`
`and source of gain transistor 654a. Capacitor 668a may include parasitic of gain
`
`

`

`[DOCKET NO. 121973]
`
`13
`
`transistor 654a. Capacitor 668a may also include a bank of switchable capacitors,
`
`which may be coupled between the gain and source of gain transistor 654a and may be
`
`used to fine-tune the input impedance of CA LNA 640a. Each switchable capacitor
`
`may be implemented with a capacitor coupled in series with a switch. Similarly, a
`
`variable capacitor 668b may be present across the gate and source of gain transistor
`
`654b. Capacitor 668b may include a bank of switchable capacitors, which may be
`
`coupled between the gain and source of gain transistor 654b and may be used to fine-
`
`tune the input impedance.
`
`[0063]
`
`Input matching circuit 632 is common to both amplifier stages 650a and 650b
`
`and is used in both the CA mode and the non—CA mode.
`
`In the CA mode, both
`
`amplifier stages 650a and 65% are enabled, and gain transistors 654a and 654b operate
`
`in a saturation region, as shown in FIG. 6B.
`
`In the non-CA mode, one amplifier stage
`
`(e.g., amplifier stage 650a) is enabled, and the other amplifier stage (e.g., amplifier
`
`stage 650b) is disabled. However, the gain transistor in the disabled amplifier stage
`
`(e.g., gain transistor 654b in amplifier stage 650b) is turned On by the input RF signal
`
`that is applied to both gain transistors 654a and 654b. Since the cascode transistor in
`
`the disabled amplifier stage (e.g., cascode transistor 656b) is turned Off,
`
`the gain
`
`transistor in the disabled amplifier stage operates in a linear region. Hence, a gain
`
`transistor may operate in the saturation region when an amplifier stage is enabled and
`
`may operate in the linear region when the amplifier stage is disabled. Operating the
`
`gain transistor of the disabled amplifier stage in the linear region may help to reduce
`
`changes in the input impedance of CA LNA 640a between the CA mode and the non—
`
`CA mode, without a current penalty in the disabled amplifier stage.
`
`In particular, the
`
`input capacitance, CIN, of a given gain transistor (e.g., gain transistor 654b) in an
`
`enabled amplifier stage and in a disabled amplifier stage may be expressed as:
`
`CIN : g - W - L - COX
`
`amplifier stage is enabled,
`
`and
`
`CIN = %- W - L- COX
`
`amplifier stage is disabled,
`
`Eq (1)
`
`Eq (2)
`
`where W is the width and L is the l