United States Patent [191
`Rotzoll
`
`[54] VOLTAGE CONTROLLED OSCILLATOR
`BAND SWITCHING TECHNIQUE
`
`[75] Inventor: Robert Rudolf Rotzoll, Allen, Tex.
`
`[73] Assignee. Mlcrotune, Inc. Plano, Tex.
`
`.
`
`~
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`-
`
`[21] Appl. No.: 577,174
`[22] Filed:
`Dec. 22,1995
`
`USO05739730A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,739,730
`Apr. 14, 1998
`
`4,353,038 10/1982
`4,442,415
`4/ 1934
`4,450,416
`5/1984
`4,536,724
`3/1985
`4,638,264
`l/1987
`4,827,226
`5/1989
`4,939,481
`7,1990
`4,999,589
`3/1991
`5,434,543
`7/1995
`5’548’252
`8/1996
`
`[51] Int. Cl.6 ................................ .. H03B 5/08; H03] 5/24
`[52]
`331/177 V; 331/179; 334/15
`[53]
`Field of Search ............................ .. 331/36 C, 177 V.
`331/179; 334/15
`
`Primary Examiner-Sieg?‘ied H. Grimm
`Attorney, Agent, or Firm-Fulbright & Jaworski L.L.P.
`[57]
`ABSTRACT
`
`[56]
`
`References cued
`U.S. PATENT DOCUMENTS
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`3,538,450 11/1970 Andrea t al. .................... .. 331/177 V
`3,611,154 10/1971 Kupfer ....... ..
`..
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`3,631,364 12/1971 Schlib et a1. .. 3,909,748 9/1975 Yuan et a1. ........................ .. 331/117 R
`
`A band switchable resonant circuit for a voltage controlled
`oscillator has an inductive component in parallel with a
`plurality of varactor diodes. Some of the varactor diodes are
`selectively switchable to control the frequency range of
`-
`-
`‘
`“mm opcmtm'
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`46 Claims, 4 Drawing Sheets
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`1 U
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`1 l
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`l
`l
`OSCILLATOR 101 I
`101
`l
`ACTIVE
`l
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`CIRCUITRY
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`1 L/
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`I
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`I
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`l
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`2
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`1114
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`103
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`102
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`1 S4
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`153
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`1 S2
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`I
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`'
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`RESONANT 1c CIRCUIT
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`I
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`12]
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`TCL EXHIBIT 1042
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`US. Patent
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`Apr. 14, 1998
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`Sheet 4 0f 4
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`5,739,730
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`OSCILLATOR
`ACTIVE
`CIRCUITRY
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`l |_______RE§9EAELQHTEULT______._1
`FIG. 8
`(PRIOR ART)
`
`99.
`
`COMPENSATOR
`DC INPUT
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`14R 9
`
`FIG. 9
`(PRIOR ART)
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`COMPENSATOR
`OUTPUT VOLTAGE AND
`VCO FREQUENCY
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`r. F
`1 O
`(PRIOR ART)
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`INPUT VOLTAGE
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`5,739,730
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`1
`VOLTAGE CONTROLLED OSCILLATOR
`BAND SWITCHING TECHNIQUE
`
`RELATED APPLICATION
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`2
`capacitors in parallel with some type of inactive or elec
`tronic circuit switch, such as a rectifying diode. A switching
`diode, or a MOS transistor could be used to add the
`capacitors.
`Another technique that is used to handle the problem of
`nonlinearity of the VCO, is to modify the input control
`voltage via a compensation circuit. The compensation cir~
`cuit predistorts the input voltage to the VCO, so as to make
`the transfer function from the input voltage to the output
`frequency linear. However, the problem with this technique
`is that it also requires the varactor diode to have large
`voltages applied to it in an effort to linearize the operating
`transfer function.
`Therefore, a VCO should not only have a broad frequency
`range, but also maintain a low gain in terms of the amount
`of output frequency variation of the output which occurs
`compared to the input voltage variation.
`Another goal is to keep the VCO gain as low as possible,
`so as to minimize the amount of noise transferred through
`the VCO, which becomes phase noise.
`Also, it is desired to have a linear transfer function of the
`input voltage to the VCO versus the output frequency.
`Furthermore, all of the individual frequency bands in the
`VCO should be approximately equal widths. In other words,
`the relationship between the loop gain of the VCO output
`frequency and the input voltage variation should remain
`constant. This is necessary for the phase lock loop perfor
`mance to remain uniform across the operating spectrum.
`It is, therefore, an object of the present invention to
`provide a voltage controlled oscillator band switching tech
`nique that limits the frequency range of any given selected
`frequency band so that a minimum amount of phase noise is
`created due to the input voltage noise on the VCO.
`Yet another object of the present invention is to provide a
`voltage controlled oscillator band switching technique that
`simpli?es the design of the switches, so that the diode is not ‘
`required to be biased with the voltage, and the capacitors
`would not require biasing.
`A still further object of the present invention is to provide
`a voltage controlled oscillator band switching technique that
`produces a linear transfer function of the VCO for the input
`voltage versus the output frequency.
`
`This application is related to Ser. No. 08/579,069. now
`US. Pat. No. 5,648,744, SYSTEM AND METHOD FOR
`VOLTAGE CONTROLLED OSClLLATOR AUTOMATIC
`BAND SELECTION, ?led concurrently with this applica
`tion and hereby incorporated by reference herein. These
`applications are commonly assigned
`
`TECHNICAL FIELD OF THE INVENTION
`
`This invention relates to voltage controlled oscillators,
`and more speci?cally, to oscillators that use phase lock loops
`and frequency synthesizers.
`
`BACKGROUND OF THE INVENTION
`
`Building a voltage controlled oscillator (VCO) that has a
`wide operating frequency range creates a problem, in that a
`wide frequency range requires a large voltage change
`applied on a varactor diode. A varactor diode is used in
`combination with an inductor to de?ne the operating fre
`quency of the VCO. In order to obtain a large change in the
`capacitance of the diode. a large variation of applied voltage
`is required. The di?iculty with integrating such a device is
`that only a limited voltage range is available in integrated
`circuit diodes.
`Another goal is to have a wide operating frequency range
`of the VCO, while low phase noise conditions are main
`tained. A problem arises when a single diode and a single
`inductor are used in a VCO, which can result in large noise
`inputs into the VCO which are then translated into large
`frequency errors. Because the phase noise of the oscillations
`is related to the input noise, it is desirable to limit how wide
`a frequency range a VCO has. One solution to this problem
`is to band switch the oscillator, which involves having
`narrow operation frequency bands that are available with the
`same varactor diode.
`The band switching technique is well known in the prior
`art, typically, and it is done using additional capacitors in the
`circuit. The capacitors are placed either in parallel or in
`series with the varactor diode. The different arrangements
`modify the total capacitance available in the inductance!
`capacitance (L/C) tank circuit. However, one problem with
`this technique is that the varactor diode capacitance range
`becomes a smaller percentage of the total capacitance range
`of all of the capacitors combined. This causes a variation in
`the frequency range for the varactor diode in any selected
`band, in that the same maximum frequency range from the
`oscillator is not achieved for a band that has low frequencies
`when compared to a band that has high frequencies. Also,
`the additional capacitors cause a change in linearity of the
`circuit, as well as a change in the available frequency range.
`The transfer function of the VCO becomes more linear as the
`additional capacitors increase in value when compared to the
`capacitance size of the varactor diode.
`Another problem is that because of nonlinearity concerns,
`the applied voltage to the varactor diode itself would vary
`over much greater ranges for an integrated application. This
`is contrary to the goal of limiting the voltage that is applied
`to the varactor diode. Other analog circuits that are tied to
`the oscillator and drive the input voltage typically are rated
`to a certain voltage range, which should be kept as large as
`possible in order to minimize noise impact. In the prior art.
`generally band switching was accomplished by placing
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`SUMTVIARY OF THE JNVENTION
`
`In accordance with the present invention, a voltage con
`trolled oscillator band switching technique is provided.
`Instead of using ?xed capacitors in parallel with the
`primary varactor diode, other diodes are placed in parallel
`with it. The varactor diode presents an appropriate amount
`of capacitance variation compared to the input voltage,
`which produces an acceptable output frequency variation.
`By switching in parallel diodes that have similar
`characteristics, the linearity of the voltage controlled oscil
`lator does not vary from one band to the next. The single
`varactor diode by itself gives the highest operating fre
`quency. For each additional diode that is added, the oper
`ating frequency range of the VCO drops down to a lower
`range.
`A digital control of some type, either transistors or switch
`ing diodes. selects the number of diodes that get added to the
`circuit. This technique insures that the VCO gain remains
`constant regardless of how many of the diodes are switched
`in parallel. Thus. the amount of output frequency variation
`versus the input voltage variation for each band is identical
`to all other bands that are possible in that VCO. Also. the
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`5,739,730
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`FIG. 2 is a schematic representation of a differential
`voltage controlled oscillator with varactor diode band
`switching.
`FIG. 3 is a schematic representation of the best mode of
`the differential voltage controlled oscillator band switching
`technique.
`FIG. 4 is a schematic representation of the basic voltage
`controlled oscillator from the prior art.
`FIG. 5 is a graphical representation of a voltage controlled
`oscillator from the prior art showing input voltage versus
`output frequency.
`FIG. 6 is a schematic representation of a voltage con
`trolled oscillator from the prior art with reduced gain via a
`parallel capacitor.
`FIG. 7 is a schematic representation of a voltage con
`trolled oscillator from the prior art with reduced gain via a
`series capacitor.
`FIG. 8 is a schematic representation of a voltage con
`trolled oscillator ?'om the prior art with capacitance band
`switching.
`FIG. 9 is a schematic representation of a VCO control
`voltage compensation system from the prior art.
`FIG. 10 is a graphical representation of the control voltage
`compensated voltage controlled oscillator transfer function
`showing input voltage versus compensator output voltage
`and voltage controlled oscillator output frequency.
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`frequency range is increased by using the band switching
`technique. However, for any given band, the amount of
`frequency variation is relatively small.
`It is therefore one technical advantage of the invention to
`provide a band switching technique that is simpli?ed
`because the same voltage that is applied to the primary
`varactor diode is also applied by the switches to the addi
`tional diodes that are added in parallel to the primary one.
`It is a further technical advantage of the present invention
`to provide a band switching technique such that the total
`frequency range available from the VCO is large, and that
`for each band that is selected, the gain of the VCO, which
`is the output frequency variation versus the input voltage
`variation, remains constant regardless of which band is
`selected.
`Thus, in accordance with one aspect of the present
`invention, there is provided a voltage controlled oscillator
`band switching technique system which generates an input
`voltage signal and converts this input voltage signal into an
`output RF signal. Preferably, the input voltage is generated
`by an oscillator active circuit and one conversion is by a
`circuit which is a resonant inductor-capacitor circuit.
`Preferably, the resonant inductor-capacitor circuit
`includes a number of switches connected in parallel to the
`input voltage signal which controls the number of junction
`diodes connected across an inductor.
`In accordance with another aspect of the present
`invention. there is provided a method for converting an input
`voltage signal into an output RF signal. comprising the steps
`of receiving an input voltage signal from a ?rst circuit
`means; processing the input voltage signal to create a ?rst
`voltage signal; and applying the ?rst voltage signal to an
`inductor to generate an output RF signal.
`Preferably. the step of processing the input voltage signal
`to create the ?rst voltage signal further comprises applying
`the input voltage signal to a capacitance to generate a ?rst
`voltage signal. Preferably, the capacitance includes a plu
`rality of ?rst junction diodes in parallel to each other, with
`each ?rst junction diode connected in series to each of a
`plurality of switches, which operate to change the total
`capacitance of the circuit.
`'
`The foregoing has outlined rather broadly the features and
`technical advantages of the present invention in order that
`the detailed description of the invention that follows may be
`better understood. Additional features and advantages of the
`invention will be described hereinafter which form the
`subject of the claims of the invention. It should be appre
`ciated by those skilled in the art that the conception and the
`speci?c embodiment disclosed may be readily utilized as a
`basis for modifying or designing other structures for carry
`ing out the same purposes of the present invention. It should
`also be realized by those skilled in the art that such equiva
`lent constructions do not depart from the spirit and scope of
`the invention as set forth in the appended claims.
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`DETAILED DESCRIPTION OF THE
`PREFERRED ElVIBODIMENT
`Before beginning a discussion of the invention, it may be
`well to review the prior art with respect to FIGS. 4-10.
`In FIG. 4, circuit 40 shows a VCO of the prior art. Block
`11 is the oscillator active circuitry. This contains the major
`ity of the oscillator with the exception of the resonant tank
`circuit 41, which contains inductor 1L1, coupling capacitor
`4C, and varactor diode 1D1. Coupling capacitor 4C is used
`to keep DC voltages from inductor 1L1. In varactor diode
`1D1, the capacitance is optimized when it is varied by the
`applied voltage across the diode lDl. In circuit 40, the VCO
`frequency is de?ned by the capacitance of varactor diode
`1D1 in combination with the inductance of inductor 1L1.
`The range of operating frequencies of circuit 40 are de?ned
`by the maximum voltage that can be applied to varactor
`diode 1D1, which causes its capacitance to change. If a large
`frequency range is desired, than a small disturbance of the
`input voltage, such as noise, will be transferred through the
`VCO, and therefore, create a phase noise in the operating
`frequency of the oscillator. Also, this voltage controlled
`oscillator circuit 40 is difficult to integrate, because
`typically, the varactor diode 1D1 cannot be supplied with a
`large voltage.
`FIG. 5 shows the change of the operating frequency of the
`VCO versus the input voltage. The VCO frequency varies in
`a nonlinear manner as shown by curve 501. The slope 502
`of curve 501 varies with the input voltage. The VCO output
`frequency at the high input voltage tends to vary relatively
`quickly. when compared to the low input voltage, which
`varies more slowly. ‘This creates an undesirable condition in
`a typical phase lock loop or frequency synthesizer applica
`tion in which it is desirable to have the VCO gain remain
`constant.
`FIG. 6. which shows circuit 60, contains oscillator active
`circuit 11. as well as resonant tank circuit 61, which includes
`inductor 1L1. varactor diode 1D1, and an additional capaci
`tor 6C. Capacitor 6C is used in parallel with varactor diode
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`For a more complete understanding of the present
`invention, and the advantages thereof, reference is now
`made to the following descriptions taken in conjunction with
`the accompanying drawings. in which:
`FIG. 1 is a schematic representation of a voltage con
`trolled oscillator with varactor diode band switching.
`FIG. 1A is a graphical representation of the voltage
`controlled oscillator input voltage versus the output fre
`quency.
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`1D1 to increase the effective capacitance of resonant tank
`circuit 61. This increase in capacitance decreases the oper
`ating frequency of the circuit 60, and also causes the
`variation of the total capacitance to decrease, since a mini
`mum capacitance from capacitor 6C is always in parallel
`with varactor diode 1D1. A secondary elfect is that because
`the variation of capacitance has been reduced relative to the
`total capacitance, the variation is somewhat more linear
`when compared to the original varactor diode 1D1 alone. A
`problem with circuit 60 is that the range of operating
`frequencies has been reduced because the capacitance varia
`tion is now smaller.
`FIG. 7 shows circuit 70, which also contains oscillator
`active circuit 11, and a new tank circuit 71, which includes
`inductor 1L1, varactor diode 1D1, and additional capacitor
`7C. Capacitor 7C increases the operating frequency of the
`resonant LC circuit by dividing the amount of capacitance
`available in circuit 70. However, the frequency range has
`also been reduced, in that a larger swing of voltage on
`varactor diode 1D1 has less of an effect on the total
`capacitance. The performance of circuit 70 is the comple
`ment of that performance of circuit 60.
`FIG. 8 shows circuit 80, which contains oscillator active
`circuit 11, as well as another variation on tank circuit 81.
`Tank circuit 81 contains inductor 1L1. varactor diode 1D1,
`capacitors 8C1, 8C2 and 8C3, as well as switches 881, 882
`and 853. The purpose of the switches SS1. 882, and 853 is
`to create additional capacitance beyond that provided by the
`varactor diode 1D1. When switch 881 is closed, capacitor
`8C1 is placed in parallel with varactor diode 1D1, which
`therefore increases the total amount of capacitance available
`to circuit 80, and simultaneously decreases the range of
`capacitance generated by voltage variation on varactor diode
`1D1. This limits the frequency range of circuit 81. If
`switches 851 and 852 are both closed simultaneously,
`capacitors 8C1 and 8C2 are placed in parallel with varactor
`diode 1D1, which further increases the capacitance available
`in tank circuit 81, as well as further decreases the operating
`frequency of tank circuit 81, and the total effect of variation
`of capacitance of varactor diode 1D1. This, in turn, makes
`the frequency variation of circuit 80 smaller than if switch
`852 were not closed.
`FIG. 9 contains controlled voltage compensator 91, volt
`age controlled oscillator 92, and circuit 90. The input to the
`controlled voltage compensator 91 is a modi?ed control
`voltage for the input to the VCO. Control voltage 902, which
`has now been modi?ed to correct for variation in gain in the
`voltage controlled oscillator, controls the VCO directly.
`VCO output 903 is the output frequency to circuit 90.
`The performance of circuit 90 is explained in FIG. 10 in
`terms of the nonlinearity of the VCO. The VCO curve 1001
`in FIG. 10 shows that the VCO output frequency varies
`tremendously for small input voltage variations at higher
`output frequencies. Compensator 91 applies curve 1002 to
`the input voltage which is now applied as signal 902 to the
`VCO. with the resulting curve 1003 of the VCO de?ned as
`the VCO output 903 versus the compensator 91 DC input
`901, which is shown as curve 1003 in FIG. 10. This produces
`a more linear transfer function of the input voltage versus
`output frequency. However. this method of linearization
`introduces additional noise since the controlled voltage
`compensator 91 has several active elements, or possibly
`even passive elements, which introduce noise. Because this
`method adds additional noise to the voltage controlled
`oscillator. it is an undesirable scheme for correction of
`nonlinearity.
`‘
`FIG. 1 shows one preferred embodiment of the present
`invention. Circuit 10 is a voltage controlled oscillator
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`(VCO) comprised of oscillator active circuit 11, and reso
`nant tank circuit 12, which de?nes the operating frequency
`of the VCO. Resonant tank circuit 12 is comprised of
`inductor 1L, capacitor 1C1, and varactor diodes 1D1, 1D2,
`1D3, and 1D4. It also contains switches 182, 133 and 184.
`Switches 152, 153 and 184 connect, and can enable diodes
`1D2, 1D3 and 1D4 in tank circuit 12 under a digital control
`signal. The performance of varactor diode 1D1, in combi
`nation with inductor 1L, de?nes the highest possible oper
`ating frequency of the VCO. As voltage is varied across
`varactor diode 1D1, a change occurs in the output frequency.
`If switch 1S2 is also closed, diodes 1D1 and 1D2 are now
`placed in parallel in the circuit 12. Therefore, diodes 1D1
`and 1D2 simultaneously affect the output frequency of the
`VCO. If switch 153 is now closed, diode IDS is also placed
`in parallel. In the preferred embodiment, with the addition of
`each parallel diode 1B2, 1B3 and 1D4, the frequency of
`operation of the VCO will decrease by an amount related to
`the effective capacitance in the diodes 1D2, 1D3, and 1D4
`which are placed in parallel.
`Signals 101 and 102 are the connection between the
`oscillator active circuitry 11 and the resonant LC circuit 12.
`These produce the AC wave form that is fed into the
`resonant LC circuit 12 that then produces the output fre
`quency of the oscillator.
`Capacitor 1C1 is used to block the DC signal which is
`applied to the diodes 1D1. 1D2, 1D3, and 1D4, from being
`placed across inductor IL. The gain of the VCO in circuit 10
`will remain constant with regard to the applied input voltage
`versus the output frequency of the VCO. This is because the
`diodes 1D1, 1B2, 1B3. and 1D4 are all of similar perfor
`mance and therefore, the linear effect of paralleling the
`capacitors produces a frequency variation which is identical
`between the bands selected by switches 152, 183 and 184.
`The frequency variation of the output of the oscillator
`when compared to the input voltage is relatively linear
`because the variation of the voltage applied to the diodes
`1B1, 1B2, 1D3, and 1D4 is small. Each of the diodes 1D1,
`1D2, 1D3. and 1D4 receive a small percentage of the total
`voltage change when compared to a normal varactor diode
`in a nonintegrated situation. Because the variation is so
`small, the gain then remains relatively constant versus the
`variation in input voltage. Another advantage is that as the
`additional diodes 1D2, 1D3, and 1D4 are added to the circuit
`12, the frequency of operation does decrease. However, the
`relative gain of the VCO, which is the variation in output
`frequency compared to the variation of input voltage,
`remains constant since diodes 1B2, 1B3 and 1D4 are all of
`similar performance. Also, because the band switching via
`switches 182, 183. and 184 selects di?erent narrow fre
`quency ranges, the noise impact from any input noise is
`reduced, since there is now a small output frequency varia
`tion due to the variation of the input voltage. Therefore,
`circuit 10 is less sensitive to input noise.
`The additional junction varactor diodes 1D2, 1D3, and
`ID! are easily constructed on an integrated circuit, as is
`varactor diode 1D1. They are inexpensive to add to circuit
`12. and as in the case of many processes, an explicit ?xed
`capacitor for use in parallel with the varactor diode may not
`be available. In virtually all processes that have a junction
`diode used as a varactor diode, parallel junction diodes are
`easy to implement and are consistent with standard inte
`grated circuit processing. Also. the cost of the additional
`diodes is small relative to the total cost of the average
`integrated circuit.
`Typically in standard processing. the voltage range
`applied to diodes 1D1. 1D2. 1D3 and 1D4 on an integrated
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`circuit would be between zero and 5 V. However, in certain
`processes, it might be larger, or even possibly reduced to 3
`V. The standard varactor diodes used in the prior art have
`ranges of approximately 30 V. Therefore, the reduction in
`voltage range is dramatic. This range reduction is important
`not only from the desire to linearize the circuit by applying
`a smaller voltage, but also because most modern integrated
`circuit processes cannot support a large voltage across the
`diode.
`FIG. 1A shows the transfer function for VCO Circuit 10.
`The VCO output frequency is plotted versus the VCO input
`voltage for dijferent conditions of switches 181, 132, 183
`and 184 being closed. Curve 101 is the transfer function of
`the VCO for the case where none of switches 1S1, 1S2, 1S3
`and 184 are closed. Curve 102 shows the VCO transfer
`function when switch 1S2 is closed. While the frequency has
`now been reduced, the gain of the VCO has remained
`constant and is identical to curve 101, only with a lower
`operating frequency. Closing switches 182 and 153 yields
`curve 103 which again lowers the operating frequency for
`the VCO, but has the same gain as in curves 101 and 102.
`Finally, closing switches 182, 183 and 184 yields curve 104,
`Which has an even lower operating frequency than the
`previous curves, but has the same gain as the previous
`curves. Note also, that while only four diodes are shown,
`circuit 10 could work with any number of diodes, and
`perhaps in some situations, the diodes could have different
`voltage ranges, and therefore can be switched in by various
`combinations of switches. This gives a wide range of control
`for the switches 182, 153 and 184, which need not be in
`sequential fashion. This control could be done in binary or
`any other method in order to yield a wide range of
`possibilities, particularly when the capacitance and voltage
`range of each diode are di?erent.
`FIG. 2, shows another preferred embodiment of the
`present invention. Circuit 20 is the differential implementa
`tion of the voltage controlled oscillator. Block 21 is the
`oscillator active circuitry which contains the differential
`oscillator element. Circuit 22 is a differential implementa
`tion of a resonant LC tank circuit. The resonant LC tank
`circuit 22 with its combination of capacitance and induc
`tance will resonate at a given operating frequency. Inductor
`2L is contained inside circuit 22, as well as diodes 2D1. 2D2,
`2D3, 2D4, 2D1', 2D2', 2D3' and 2D4', as well as switches
`282, 283, 284. 252', 283’ and 254’. The effect of diodes 2D1
`and 2D1' is to vary the capacitance of those diodes with
`respect to the input voltage. As the voltage is varied, the
`capacitance varies, therefore the operating frequency of the
`tank circuit as built via diodes 2D1 and 2D1' and inductor 2L
`will vary.
`One of the purposes of adding diode 2D1' was to remove
`the coupling capacitor that would normally be used with
`inductor 2L. This capacitance would be used to block a DC
`voltage to the inductor 2L. The con?guration of diodes 2D1
`and 2D1' is such that the control voltage is applied to the
`connection between the two, and the connections to the
`inductor 2L now are at the same DC voltage, although they
`are always going to be at opposing AC voltages. A secondary
`advantage of having a differential implementation with
`regard to an integrated circuit is that the amount of coupling
`noise into the substrate of the integrated circuit is dramati
`cally reduced by using a differential implementation of the
`resonant LC circuit 22.
`Circuit 20 is the preferred embodiment for a case of using
`an integrated circuit which has many other analog compo~
`nents. This is because the signals generated by circuit 20 are
`less likely to couple into the other analog circuits which are
`
`45
`
`50
`
`55
`
`65
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`5 ,739,730
`
`10
`
`25
`
`35
`
`8
`available on the same integrated circuit via the substrate of
`the integrated circuit. Circuit 10 is the preferred embodiment
`for an integrated circuit Whose sole purpose is to be a voltage
`controlled oscillator, or perhaps, in an implementation that
`is not integrated.
`FIG. 3 shows the best mode contemplated for circuit 20
`of FIG. 2. In FIG. 3, switches 282 through 286' comprise
`end channel MOS ?eld effect transistors, which are applied
`as switches in the sense that when one of the digital switch
`control inputs has a high voltage applied to it, the transistor
`will then create a low resistance between the source and the
`drain regions of that device. Typically, these switches have
`dimensions of widths of 2 microns, lengths of 800
`nanometers, and a multiplicity of 1.
`Diodes 2D through 2D6' in this embodiment are the
`junction diodes which are con?gured as the varactor diodes
`in the voltage controlled oscillator. They comprise PN
`junctions, which are each de?ned as a P+ diffusion in a N
`well region of an integrated circuit process.
`Inputs B0 through B4 are used to control the switches 282
`through 286', and these inputs receive digital logic control
`signals from internal circuitry. Typically, these are signals
`from zero to 5 V, which can be switched externally. VIN
`which is connection 201, ranges from 1 to 4 V.
`Typically, oscillator active circuitry 21 would include the
`power supply VDD, which is a positive voltage with respect
`to power supply VSS. The VDD minus VSS level is usually 5
`V, however, it can range from 4 to 6 V. Transistors 3T1 and
`3T2 are both MOS P channel ?eld etfect transistors which
`are con?gured to act as current sources under the control of
`voltage VBIAS and are set to a nominal current, which
`enables the oscillator circuit. Transistors 3T3 and 3T4 are
`the core of the oscillator; they utilize a cross-coupled
`scheme to create a negative resistance, which under the
`current bias from transistors 3T1 and 3T2 will cause oscil
`lation when tied to the tank circuit de?ned by inductor 2L
`and diodes 2D1 through 2D6'. Transistors 3T5 and 3R1
`comprise an ampli?er, as does transistor 3T6 and 3R2. These
`ampli?ers take the VCO output, and shift the level to one
`that is close to the VDD signal, and then increase the signal
`level to a large voltage swing, typically on the order of
`approximately 800 mV.
`The present invention, therefore. is well adapted to carry
`out the objects and obtain the ends and advantages men
`tioned as well as others inherent therein. While presently
`preferred embodiments of the invention have been given for
`the purpose of disclosure, numerous changes in the details of
`construction and arrangement of parts will be readily appar
`ent to those skilled in the art and which are encompassed
`within the spirit of the invention and the scope of the
`appended claims.
`Although the present invention and its advantages have
`been described in detail, it should be understood that various
`changes, substitutions and alterations can be made herein
`without departing from the spirit and scope of the invention
`as de?ned by the appended claims.
`I claim:
`1. A band switching resonant circuit for a voltage con
`trolled oscillator. said circuit comprising:
`an inductor connected in series with a capacitor. wherein
`a single current ?ows through both said inductorand
`said capacitor;
`a ?rst diode connected across the series connection of the
`inductor and the capacitor; and
`at least one other diode selectively switchable across said
`?rst diode;
`
`TCL EXHIBIT 1042
`Page 9 of 11
`
`

`
`9
`wherein said ?rst diode and said other diode provide
`voltage controlled variable capacitance.
`2. The invention set forth in claim 1 further comprising at
`least one transistor switch connected to said other diode for
`switching said other diode into said circuit.
`3. The invention set forth in claim 1, wherein:
`said ?rst diode is selectively switchably connected across
`the series connection of the inductor and the capacitor.
`4. The invention set forth in claim 1, wherein:
`said ?rst diode is ?xedly connected across the series
`connection of the inductor and the capacitor.
`5. The invention set forth in claim 1, wherein:
`said at least one other diode is a plurality of other diodes.
`each selectively switchable across said ?rst diode.
`6. The invention set forth in claim 1, wherein:
`said ?rst diode and said at least one other diode are
`junction diodes.
`7. The invention set forth in claim 1, wherein:
`said ?rst diode and said at least one other diode are
`varactor diodes.
`8. Amethod for controlling the operating frequency of an
`oscillator, the method comprising the step of:
`selecting a frequency band of the oscillator by changing
`a capacitance of a resonant circuit; and
`selecting a frequency in said frequency band by varying
`the voltage applied to said resonant circuit;
`wherei