`Tayloe
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,230,000 B1
`May 8, 2001
`
`U300623000031
`
`(54) PRODUCT DETECTOR AND METHOD
`THEREFOR
`
`(75)
`
`Inventor: Daniel Richard Tayloe, Phoenix, AZ
`(Us)
`
`(73) Assignee: Motorola Inc., Schaumburg, IL (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U-S-C- 154(b) by 0 days.
`
`(21) Appl. No.: 09/173,030
`.
`Oct. 15’ 1998
`Ffled:
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`Int. Cl.7 ................................ H0413 1/26; H0413 1/00
`(51)
`(52) US. Cl.
`.......................... 455/323; 455/303; 455/304;
`455/313
`(58) Field of Search ..................................... 455/302, 303,
`455/304 324 338 339 313 318 323.
`375/323 329 332. 327/113 45. 329/304
`’
`’
`’
`’
`References Cited
`
`(56)
`
`U'S' PATENT DOCUMENTS
`4,847,860 *
`7/1989 Robert .................................. 375/136
`10/1989 Saulnier et a1.
`4,878,029
`329/341
`
`..... 342/68
`..
`5,150,124
`9/1992 Moore et a1.
`
`5,339,459
`8/1994 Schiltz etal.
`-- 455/333
`5,355,103 * 10/1994 Kozak ........
`
`455/289
`.. 375/316
`
`' 4:5/314
`232142111:
`*
`3133:; Kgifms
`578057093
`9/1998 Heikkilizineitnal """"""""""""
`”
`5,838,675 * 11/1998 Rauscher ......'..:..................... 370/343
`5,999,574 4 12/1999 Sun et a1.
`375/325
`
`6/2000 Sokoler ,,,,,,
`6,073,001 *
`455/323
`7/2000 Bickley et a1.
`...................... 455/131
`6,088,581 *
`
`FOREIGN PATENT DOCUMENTS
`
`2294169
`9110283
`9602977
`
`9838732
`
`9/1995 (GB)
`12/1990 (W0)
`7/1995 (W0)
`
`............................... H03D/7/OO
`H03D/3/00
`H04B/1/26
`
`
`24998 (W0) ------------------------------ H03D/7/00
`OTHER PUBLICATIONS
`
`Article entitled “A 1.5 GHZ Highly Linear CMOS Down—
`conversion Mixer” published in IEEE Journal of Solid—State
`Circuits, vol. 30, No. 7, Jul. 1995.
`Article entitled “Recent Advances in Shortwave Receiver
`Design” by Dr. Ulrich L. Rohde in QST, Nov. 1992.
`Article “Asymmetric Polyphase Networks” by MJ. Gin gel]
`in Electrical Communication, vol. 48, No. 1 and 2, 1973.
`Aritcle entitled “High—Performance, Single—Signal Direct—
`Conversion Receivers” by Rick Campbell —QST Magazine
`(Jan- 1993)-
`* cited by examiner
`_
`_
`Primary Examiner—Dwayne Bost
`Assistant Examiner—Raymond B. Persino
`(74) Attorney, Agent, 01‘ Firm—Dana B. LCMOlnC; Timothy
`J. Lorenz; Frank J. Bogacz
`(57)
`ABSTRACT
`
`to baseband
`A product detector for converting a signal
`includes a commutating switch which serves to sample an
`RF waveform four times per period at the RF frequency. The
`samples are integrated over time to produce an average
`voltage at 0 degrees, 90 degrees, 180 degrees and 270
`degrees. 'lhe average voltage at 0 degrees is the baseband
`in-phase signal, and the average voltage at 90 degrees is the
`baseband quadrature signal. Alternatively, to increase gain,
`the 0 degree aVerage can be differentially summed With the
`180 degree average to form the baseband in-phase signal,
`and the 90 degree average can be differentially summed with
`the 270 degree average to produce the baseband quadrature
`'
`l,
`“gm
`
`0691733
`
`6/1995 (EP)
`
`.............................. H03B/21/00
`
`14 Claims, 3 Drawing Sheets
`
`BIAS
`NETWORK
`
`.34
`
`50
`
`BASEBAND
`INPHASE
`
`BASEBAND
`QUADRA TURE
`
`r-----l----1
`
`
`
`
`Intel v. ParkerVision
`
`|PR2020-01265
`
`Intel 1027
`
`INTEL 1004
`
`Intel v. ParkerVision
`IPR2020-01265
`Intel 1027
`
`
`
`US. Patent
`
`May 8,2001
`
`Sheet 1 0f3
`
`US 6,230,000 Bl
`
`f1-fo,fo-f1
`
`,0 FIG- 1
`
`f0
`
`— PRIOR ART —
`
`
`
`PHASE I +
`
`DELAY
`
`—
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`f0'f10R f1‘f0
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`20
`FIG- 2 —
`
`— PRIOR ART —
`
`
`
`162
`
`158
`
`BA SEBA ND
`
`0T?INPHASE
`f1 fl—J c;j
`BASEBAND
`V |
`|154
`OUADRA TURE
`
`150
`
`
`
`NETWORK
`
`
`50
`r----i---1
`
`BASEBAND
`INPHASE
`
`BIAS
`
`
`
`.38
`
`
`BA SEBA ND
`QUADRA TURE
`
`
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`waned'S'fl
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`100z‘8Km
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`‘8J0Z103118
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`HI000‘09Z‘9Sfl
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`
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`US. Patent
`
`May 8,2001
`
`Sheet 3 0f 3
`
`US 6,230,000 B1
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`1’1
`
`
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`202
`
`
`
`4 : l
`ANALOG
`MUX
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`
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`00
`
`_, 900
`
`I
`2,2
`
`J.
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`T‘zoe T‘zoa
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` 2-B IT
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`DIGITAL
`
`
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`COUNTER
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`2
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`222
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`199
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`220 FIG. 7
`
`f1
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`USB/L SB
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`4 f1
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`
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`US 6,23 0,000 B1
`
`1
`PRODUCT DETECTOR AND METHOD
`THEREFOR
`
`FIELD OF THE INVENTION
`
`This invention relates in general to radio receivers and, in
`particular, to the converting of signals in frequency.
`
`BACKGROUND OF THE INVENTION
`
`Direct conversion receivers are desirable in part because
`they convert signals of interest directly to baseband (or near
`zero hertz) from a radio frequency (RF) or an intermediate
`frequency (IF). Simple direct conversion receivers, such as
`receiver 10 shown in FIG. 1, suffer from multiple draw—
`backs. The RF signal f1 is mixed with the local oscillator
`signal f0, and the signal of interest fl—fD is produced at
`baseband at the output. Unfortunately, superimposed on the
`signal of interest is the image fO—fl. The “image problem” of
`simple direct conversion receivers is well known in the art
`of receiver design, the solution to which has been the subject
`of scholarly study for decades.
`Image reject mixers, such as mixer 20 in FIG. 2, have
`been developed in response to the image problem suffered
`by simple direct conversion receivers. The operation of
`image reject mixers, including the mathematical basis upon
`which they operate,
`is described in detail
`in “High—
`Performance, SingleASignal DirectAConversion Receivers”
`by Rick Campbell, published in the January, 1993 issue of
`QST magazine. Image reject mixers utilize two local oscil—
`lator signals, each differing from the other by 90 degrees in
`phase. Image reject mixers also require the use of two
`separate mixer elements. Image reject receivers represent a
`complex and expensive solution to the image problem of
`direct conversion receivers.
`
`Both simple direct conversion receivers and image reject
`mixers nominally exhibit a loss of 6 dB because half of the
`signal is converted to f0+f1, the sum of the RF frequency and
`the local oscillator frequency, and then discarded.
`In
`practice, the loss is often greater than 6 dB because con—
`ventional mixers are typically implemented with diodes
`which exhibits a finite amount of loss themselves. Typical
`conversion loss in prior art image reject mixers is 778 dB.
`What is needed is a lowiloss method and apparatus for
`simply and inexpensively overcoming the image problem of
`direct conversion receivers.
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`FIG. 1 shows a prior art direct conversion receiver;
`FIG. 2 shows a prior art image reject mixer;
`FIG. 3 shows a direct conversion receiver in accordance
`with a preferred embodiment of the present invention;
`FIG. 4 shows a waveform in accordance with a preferred
`embodiment of the present invention;
`FIG. 5 shows a product detector in accordance with a
`preferred embodiment of the present invention;
`FIG. 6 shows a product detector in accordance with an
`alternate embodiment of the present invention; and
`FIG. 7 shows a product detector in accordance with an
`alternate embodiment of the present invention.
`DETAILED DESCRIPTION OF THE DRAWINGS
`
`The method and apparatus of the present invention rep—
`resent a simple and inexpensive product detector which
`facilitates the conversion of a signal to baseband without the
`unwanted image from interfering. A commutating switch is
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`used in combination with capacitors to integrate portions of
`the input signal. The iniphase and quadrature signals that
`result represent the signal of interest at baseband.
`Turning now to the drawings in which like reference
`characters indicate corresponding elements throughout the
`several views, attention is first directed to FIG. 3. FIG. 3
`shows a direct conversion receiver in accordance with a
`preferred embodiment of the present invention. Direct con—
`version receiver 30 includes resistor 32, bias network 34,
`commutating switch 38, capacitors 72, 74, 76, and 78,
`summing amplifiers 50 and 52, phase delay 58, and sumi
`ming amplifier 60.
`In operation, an RF or IF signal fl is received at resistor
`32. Resistor 32, as is more fully discussed below, forms a
`filter when taken in combination with capacitors 72—78.
`After passing through resistor 32, the input signal is received
`by commutating switch 38 at input 36. Commutating switch
`38 switches input 36 to outputs 42, 44, 46, and 48. The rate
`at which commutating switch 38 operates is controlled by a
`signal present at control input 40. In the preferred embodii
`ment as shown in FIG. 3, the control signal input to control
`input 40 is substantially equal
`to four
`times the local
`oscillator frequency that would exist in a simple direct
`conversion receiver. As a result, input 36 is switched to each
`of the four outputs substantially once during each period of
`the input signal f1.
`In a preferred embodiment, commutating switch 38
`remains closed at each of the four outputs for substantially
`90 degrees at the frequency of the input signal. In alternate
`embodiments, commutating switch 38 remains closed at
`each of the four outputs for less than 90 degrees.
`During the time that commutating switch 38 connects
`input 36 to output 42, charge builds up on capacitor 72.
`Likewise, during the time commutating switch 38 connects
`input 36 to output 44, charge builds up on capacitor 74. The
`same principle holds true for capacitors 76 and 78 when
`commutating switch 38 connects input 36 to outputs 46 and
`48 respectively. As commutating switch 38 cycles through
`the four outputs, capacitors 72—78 charge to voltage values
`substantially equal to the average value of the input signal
`during their respective quadrants. Each of the capacitors
`functions as a separate integrator, each integrating a separate
`quarter wave of the input signal. This principle is described
`more fully with respect to FIG. 4 below.
`Output 42 rep resents the average value of the input signal
`during the first quarter wave of the period, and is termed the
`0 degree output. Output 44 represents the average value of
`the input signal during the second quarter wave of the
`period, and is termed the 90 degree output. Output 46
`represents the average value of the input signal during the
`third quarter wave of the period, and is termed the 180
`degree output. Output 48 represents the average value of the
`inputsignal during the fourth quarter wave of the period, and
`is termed the 270 degree output.
`to
`The outputs of commutating switch 38 are input
`summing amplifiers 50 and 52. Summing amplifier 50
`differentially sums the 0 degree output and the 180 degree
`output,
`thereby producing baseband iniphase signal 54.
`Summing amplifier 52 differentially sums the 90 degree
`output and the 270 degree output, thereby producing basei
`band quadrature signal 56. Baseband in—phase signal 54 and
`baseband quadrature signal 56 are input to phase delay 58
`which shifts the phase of baseband quadrature signal 56 by
`90 degrees relative to baseband iniphase signal 54. The
`resulting signals are then summed by summing amplifier 60
`to produce the signal of interest 62.
`
`
`
`US 6,230,000 B1
`
`3
`The combination of resistor 32, commutating switch 38,
`and capacitors 72—78 form a portion of a preferred embodi—
`ment of a product detector. This product detector is referred
`to herein as a “Tayloe Product Detector.” The Tayloe Prodi
`uct Detector has many advantages. One advantage is low
`conversion loss. The Tayloe Product Detector can exhibit
`less than 1 dB ofconversionloss, which is 6—7 dB improve—
`ment over the typical conversion loss of 7—8 dB in the prior
`art. This 677 dB conversion loss improvement translates into
`a 677 dB improvement in overall receiver noise figure. The
`noise figure improvement results in substantial receiver
`performance gains,
`in part because a pre-amplifier may
`become unnecessary as a result. The use of a pre—amplifier,
`while improving receiver noise figure by overcoming front
`end receiver loss, causes large signal performance to suffer
`due to an amplified highilevel input signal overloading the
`input mixer. Because the Tayloe Product Detector signifi
`cantly reduces front end loss,
`the pre—amplifier and its
`associated problems may become unnecessary in future
`direct conversion receiver designs.
`Another advantage of the Tayloe Product Detector is its
`narrowband detection characteristic. Resistor 32 and each of
`
`capacitors 72—78 form lowpass filters. The commutating
`effect of the four capacitors turns the lowpass response into
`a bandpass response centered on f1. The width of the
`bandpass is easily set by proper selection of resistor 32 and
`capacitors 72778.
`Prior art high-performance receivers often use a highly
`selective bandpass filter in front of the mixer. The width of
`the filter is set to cover the entire range over which the
`receiver can be tuned. The more selective the filter,
`the
`higher the insertion loss, which in turn decreases the sensi
`tivity of the receiver. In contrast, the narrowband character—
`istic of the Tayloe Product Detector is such that it is naturally
`centered on the frequency to which the detector is set.
`Substantial
`rejection is achieved outside the detection
`bandwidth, and as a result, front end filtering requirements
`along with the associated insertion loss are reduced, result
`ing in higher sensitivity.
`FIG. 4 shows a waveform in accordance with a preferred
`embodiment of the present
`invention. Waveform 100
`includes signal 125 which corresponds to the input signal f1.
`Superimposed on signal 125 are points 105, 110, 115, and
`120. Point 105 represents the voltage to which capacitor 72
`(FIG. 3) charges. Likewise, point 110 represents the voltage
`to which capacitor 74 charges, point 115 represents the
`voltage to which capacitor 76 charges, and point 120 rep
`resents the voltage to which capacitor 78 charges. One
`skilled in the art will understand that if f1 is a carrier signal
`with no information signal superimposed, and the carrier
`signal frequency is exactly equal to f0, four evenly spaced
`samples of f1 will continuously be taken by the action of the
`Tayloe Product Detector, and the voltages represented by
`points 105, 110, 115, and 120 will be stationary. Stationary
`voltages on the integrating capacitors 72—78 represent no
`signal of interest at baseband.
`The operation just described is the case where f1 is a pure
`carrier and the local oscillator is tuned to bring the carrier to
`zero Hz so that no signal is present at baseband. The tuning
`operation of the Tayloe Product Detector can be best under,
`stood by way of example where the tuning is not as in the
`previous example, but rather is slightly off. By way of
`example, assume that the Tayloe Product Detector of FIG. 3
`has input signal f1 and control signal 4f0 where fO differs in
`frequency by Af, that is, flifD=Af. Referring now to FIG. 4,
`points 105, 110, 115, and 120 will not be stationary, but
`instead will move along the contour of f1, because f1 does
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`not exactly equal 4fD. Points 105, 110, 115, and 120, which
`represent the integrated voltages on capacitors 72—78, will
`change at a rate equal to Af, which is the frequency of the
`signal of interest at baseband. One skilled in the art will
`understand that when information bearing signals are super
`imposed on f1, the Tayloe Product Detector translates those
`information bearing signals to baseband in the same manner
`that Af is converted to baseband in the previous example.
`FIG. 5 shows a product detector in accordance with a
`preferred embodiment of the present
`invention. Product
`detector 150 includes resistor 152, commutating switch 154,
`and capacitors 156 and 157. Commutating switch 154 is
`controlled by a signal present at control input 153. Product
`detector 150 differs from the product detector embodied in
`FIG. 3 in that only two outputs exist. Commutating switch
`154 samples the input signal f1 at two points rather than at
`four points as in FIG. 3. Commutating switch 154 creates the
`baseband in-phase signal 158 by connecting input 151 to
`output 162 once for each period of the input signal
`f1.
`Commutating switch 184 also creates the baseband quadrai
`ture signal 160 by connecting input 151 to output 164 once
`for each period of the input signal f1. Input 151 is connected
`to outputs 162 and 164 at points in time which represent
`substantially 90 degrees at the frequency of the input signal
`f1. Commutating switch 154 preferably remains closed for
`substantially 90 degrees of the input signal f1 for each of
`outputs 162 and 164.
`In operation, under control of control signal f2 at input
`153, commutating switch 154 operates as follows: input 151
`is connected to output 162 forsubstantially 90 degrees at the
`frequency of the input signal f1 thereby allowing capacitor
`157 to charge to the average value of the input signal during
`the period which commutating switch 154 was closed on
`output 162. Then, input 151 is connected to output 164 for
`substantially 90 degrees at the frequency of the input signal
`f1 thereby allowing capacitor 156 to charge to the average
`value of the input signal during the period which commu—
`tating switch 154 was closed on output 164. As a result of
`the operation of product detector 150, baseband in-phase
`signal 158 and baseband quadrature signal 160 represent
`integrated samples of the input waveform where the samples
`have been taken substantially 90 degrees apart. Product
`detector 150 can be substituted into direct conversion
`
`receiver 30 (FIG. 3) to reduce the parts count at the expense
`of some gain.
`FIG. 6 shows a product detector in accordance with an
`alternate embodiment of the present
`invention. Product
`detector 170 shows an alternate embodiment in which each
`
`integrating capacitor has its own resistor. For example, 0
`degree output 180 has a voltage controlled by the combi—
`nation of capacitor 175 and resistor 171. Likewise, 90
`degree output 182 has a voltage controlled by the combi—
`nation of capacitor 176 and resistor 172, 180 degree output
`184 has a voltage controlled by the combination of capacitor
`177 and resistor 173, and 270 degree output 188 has a
`voltage controlled by the combination of capacitor 178 and
`resistor 174. Resistor 171 and capacitor 175 form a first
`integrator. The commutating switch of product detector 170
`connects the input to this first integrator for substantially 90
`degrees of the input signal. One skilled in the art will readily
`understand that the remaining resistor/capacitor pairs also
`form integrators, each of which preferably integrates for
`substantially 90 degrees of the input signal.
`In one
`embodiment, all resistor/capacitor pairs have the same
`values, and in alternate embodiments, the resistor capacitor
`pairs have different values. In these alternate embodiments
`the separate integrators can have different time constants.
`
`
`
`US 6,230,000 B1
`
`5
`FIG. 7 shows a product detector in accordance with an
`alternate embodiment of the present
`invention. Product
`detector 200 includes analog multiplexer 202 and digital
`counter 220. Input signal f1 is received at resistor 204 and is
`then input to analog multiplexer 202. Analog multiplexer
`202 is controlled by control signals 214 which are generated
`by digital counter 220. Digital counter 220 runs at a clock
`frequency of substantially 4f1. One skilled in the art of
`analog and digital circuit design will readily understand that
`input signal f1 is connected to each of the four outputs of
`analog multiplexer 202 for substantially 90 degrees of the
`input signal. As embodied in FIG. 7, 0 degree output210 and
`90 degree output 212 are used to generate baseband inip hase
`and quadrature signals. Of course, the remaining two outputs
`(180 degrees and 270 degrees) can be utilized as embodied
`in FIG. 3 to achieve greater gain.
`Digital counter 220 includes up/down control 224. When
`digital counter 220 counts up, output 210 is the 0 degree
`output and output212 is the 90 degree output When digital
`counter 220 counts down, the opposite is true. When count—
`ing down, output 210 represents the 90 degree output and
`output 212 represents the 0 degree output The Tayloe
`Product Detector, therefore, provides for a simple and effii
`cient mechanism to switch from the image above the carrier
`to the image below the carrier. One well—known common
`used for switching between images is for switching between
`upper side band (USB) and lower side band (LSB) when
`listening to single side band (SSE) transmissions.
`
`EXPERIMENTAL RESULTS
`
`A direct conversion receiver which utilizes a Tayloe
`Product Detector has been built The receiver design is the
`same as direct conversion receiver 30 (FIG. 3) utilizing an
`analog multiplexer and a digital counter as shown in FIG. 7.
`The analog multiplexer
`is
`a Texas Instruments
`SN74BCT3253D. The digital counter is an industry standard
`74ACT163. The analog multiplexer is a 5 volt part which
`has an effective input range of substantially zero to four
`volts. Bias network 34 biases the input of the analog
`multiplexer to substantially 2 volts. This represents the
`ability to handle input signals of up to substantially +19
`dBm. This is advantageous in part because typical maximum
`signal ranges for prior art diode mixers is substantially +7
`dBm. A further advantage is that analog multiplexers
`capable of operating at higher voltages can be readily
`obtained or easily designed, thereby increasing the dynamic
`range further.
`The prototyped direct conversion receiver has an input
`bandwidth of roughly 1 kHz centered at 7 MHz. This was
`accomplished with resistor 32 at 50 ohms, and each of
`capacitors 72—78 at 0.3 microfarads. The clock input to the
`SN74ACT163 digital counter is nominally 28 MHz, and the
`receiver is tuned by varying this clock frequency. It
`is
`possible to build receivers at much higher frequencies, the
`only limitation being the rate at which the signal can be
`commutated through the integrators, which at the time of
`this writing is many orders of magnitude greater than the
`prototyped unit. The scope of the present
`invention is
`intended to include receivers at these higher frequencies.
`In summary, the method and apparatus of the present
`invention provides an advantageous means for generating
`baseband iniphase and quadrature signals from an RF or IF
`signal. While we have shown and described specific embodi—
`ments of the present invention, further modifications and
`improvements will occur to those skilled in the art For
`example, the method and apparatus of the present invention
`
`6
`have been described primarily in the context of direct
`conversion receivers; however, the Tayloe Product Detector
`is applicable anywhere signals need to be converted to
`baseband, such as in the last stage of a superheterodyne
`receiver. We desire it to be understood, therefore, that this
`invention is not limited to the particular forms shown and we
`intend in the appended claims to cover all modifications that
`do not depart from the spirit and scope of this invention.
`What is claimed is:
`1. A product detector for detecting a signal of interest at
`an input frequency, and producing baseband in—phase and
`quadrature signals which represent
`the signal of interest,
`said product detector comprising:
`an input port;
`an in—phase output port;
`a quadrature output port;
`a commutating switch having an input coupled to the
`input port of the product detector, and having a zero
`degree output coupled to the in—phase output port, a 90
`degree output coupled to the quadrature output port, a
`180 degree output, and a 270 degree output, wherein
`the commutating switch couples the input to each of the
`four outputs in a periodic fashion at a rate of substan
`tially four times the input frequency, thereby coupling
`the input to each of the four outputs substantially once
`during each period of the input frequency;
`a first charge storage device coupled between the zero
`degree output and a reference potential;
`a second charge storage device coupled between the 90
`degree output and the reference potential;
`a third charge storage device coupled between the 180
`degree output and the reference potential; and
`a fourth charge storage device coupled between the 270“
`degree output and the reference potential.
`2. The product detector of claim 1 further comprising a
`resistor coupled between the input port of the product
`detector and the input of the commutating switch.
`3. The product detector of claim 1 further comprising:
`a first differential summer responsive to the zero degree
`output and the 180 degree output, said first differential
`summer having an output coupled to the inphase output
`port; and
`a second differential summer responsive to the 90 degree
`output and the 270 degree output, said second differ
`ential summer having an output coupled to the quadra—
`ture output port
`4. The product detector of claim 1 further comprising:
`a first resistor coupled between the zero degree output and
`the first charge storage device;
`a second resistor coupled between the 90 degree output
`and the second charge storage device;
`a third resistor coupled between the 180 degree output and
`the third charge storage device; and
`a fourth resistor coupled between the 270 degree output
`and the fourth charge storage device, wherein the
`inphase output port is coupled to a point between the
`first resistor and the first charge storage device, and the
`quadrature outputport is coupled to a point betweenthe
`second resistor and the second charge storage device.
`5. The product detector of claim 1 wherein the commu—
`tating switch includes a control input responsive to which
`the switch commutates.
`
`IS. The product detector of claim 5 further comprising a
`controller having an output coupled to the control input of
`the commutating switch.
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`US 6,230,000 B1
`
`7
`7. The product detector of claim IS wherein the controller
`comprises a digital counter.
`8. The product detector of claim 1 wherein the commui
`tating switch comprises an analog multiplexor.
`9. The product detector of claim 8 further comprising a
`bias circuit on the input to the commutating switch.
`10. An apparatus for generating baseband inphase and
`quadrature signals from an input signal having a carrier
`frequency, said apparatus comprising:
`a first integrator having an input periodically coupled to
`the input signal for a first time portion of the input
`signal;
`a second integrator having an input periodically coupled
`to the input signal for a second time portion of the input
`signal, wherein the first time portion of the input signal
`and the second time portion of the input signal are
`separated by substantially 90 degrees at
`the carrier
`frequency;
`a third integrator having an input periodically coupled to
`the input signal for a third time portion of the input
`signal; and
`a fourth integrator having an input periodically coupled to
`the input signal for a fourth time portion of the input
`signal, wherein the third time portion of the input signal
`and the second time portion of the input signal are
`separated by substantially 90 degrees at
`the carrier
`frequency, and wherein the fourth time portion of the
`
`8
`input signal and the third time portion of the input
`signal are separated by substantially 90 degrees at the
`carrier frequency.
`time
`11. The apparatus of claim 10 wherein the first
`portion of the input signal
`is substantially equal
`to 90
`degrees at the carrier frequency, and the second time portion
`of the input signal is substantially equal to 90 degrees at the
`carrier frequency.
`time
`12. The apparatus of claim 10 wherein the first
`portion of the input signal is equal to less than 90 degrees at
`the carrier frequency and the second time portion of the
`input signal is equal to less than 90 degrees at the carrier
`frequency.
`13. The apparatus of claim 10 wherein the first integrator
`further includes an output for producing the baseband
`inphase signal, and the second integrator further includes an
`output for producing the baseband quadrature signal.
`time
`14. The apparatus of claim 10 wherein the first
`portion of the input signal
`is substantially equal
`to 90
`degrees at the carrier frequency, the second time portion of
`the input signal is substantially equal to 90 degrees at the
`carrier frequency, the third time portion of the input signal
`is substantially equal to 90 degrees at the carrier frequency,
`and the forth time portion of the input signal is substantially
`equal to 90 degrees at the carrier frequency.
`*
`*4
`*4
`*
`*
`
`5
`
`10
`
`15
`
`20
`
`25
`
`