Abstract:
A gain controlled mixer for an integrated CMOS transceiver. Accuracy of the controlled gain may be relatively invariant over temperature, manufacturing process, and other variations attendant to circuit realizations in a CMOS transceiver, and other realizations. A plurality of substantially matched circuit elements are instantiated and disposed similarly within the gain controlled mixer, enhancing the gain accuracy of selectable gain control states. Matching gain and other functions between circuit elements is further enhanced by appropriately controlling DC operating point conditions.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is generally related to a transceiver. More particularly, the present invention relates to a method and apparatus for achieving mixing and gain control.  
       BACKGROUND OF THE INVENTION  
       [0002]     A transceiver is a device, containing a transmitter and a receiver, which is thus capable of transmitting and receiving communication signals, respectively. Conventionally, the transmitter contains a power amplifier (PA) that provides the last stage of amplification of the signal to be transmitted.  
         [0003]     In some conventional designs, the power amplifier is implemented as a component that is physically separate from other parts of the transmitter and/or transceiver. Also, power amplifiers made from gallium arsenide (GaAs) or silicon bipolar junction transistors (SiBJT) are typically used because they have an inherently higher breakdown voltage than transistors made in a CMOS circuit, whether the transistors are n-channel or p-channel transistors. While such designs allow for a power amplifier that has the desired amplification characteristics, they do so at the expense of cost. Not only is a GaAs, SiBJT or other non-CMOS power amplifier transistor costlier than a transistor in a CMOS integrated circuit, but the non-CMOS power amplifier cannot be formed on the same integrated circuit chip as the components of the transmitter and/or transceiver. Both of these factors add to the overall cost of the resulting transceiver.  
         [0004]     It has been recognized that it would be beneficial to have a transceiver in which most of the transmitter and receiver circuits are on a single chip, including the power amplifier. For example, in the article entitled A Single Chip CMOS Direct-Conversion Transceiver for 900 MHz Spread Spectrum Digital Cordless Phones by T. Cho et al. that was presented at the 1999 IEEE International Solid State Circuits Conference, there is described a CMOS transceiver chip that includes an integrated power amplifier. An improved CMOS power amplifier is also described in the application entitled CMOS TRANSCEIVER HAVING AN INTEGRATED POWER AMPLIFIER, bearing application Ser. No. 09/663,101, filed on Sep. 15, 2000 and assigned to the same assignee as the assignee of the invention described herein, which recognizes the advantage of integrating the power amplifier.  
         [0005]     Nevertheless, some CMOS power amplifiers exhibit power level variation due to their sensitivity to thermal and process variations. These sensitivities may limit the accuracy of conventional means of providing variable gain in a CMOS power amplifier. High efficiency and constant power levels in CMOS power amplifiers may be impeded by low breakdown voltage, low current drive, and lossy substrate.  
         [0006]     Accordingly, an improved gain control technique for transceivers would be useful.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.  
         [0008]     The above, and other objects, features, and advantages of the present invention are further described in the detailed description which follows, with reference to the drawings by way of non-limiting exemplary embodiments of the present invention, wherein like reference numerals represent similar parts of the present invention throughout several views and wherein  
         [0009]      FIG. 1  illustrates a block diagram of an embodiment of a gain controlled mixer (GCM) according to the present invention.  
         [0010]      FIG. 2  illustrates a block diagram of an embodiment of a gain block cell (GBC) according to the present invention.  
         [0011]      FIG. 3A  illustrates a schematic diagram of an embodiment of a gain conversion block pair (GCBP) according to the present invention.  
         [0012]      FIG. 3B  illustrates a schematic diagram of an embodiment of a gain conversion block pair GCBP according to the present invention.  
         [0013]      FIG. 3C  illustrates a schematic diagram of an embodiment of a gain conversion block pair GCBP according to the present invention.  
         [0014]      FIG. 4  illustrates a block diagram of a gain controlled mixer including first and second conversion stages according to an embodiment of the present invention.  
         [0015]      FIG. 5  illustrates a schematic diagram of a gain controlled mixer including first and second conversion stages according to the present invention.  
         [0016]      FIG. 6  illustrates a schematic diagram of current source bias circuits.  
         [0017]      FIG. 7  illustrates a schematic diagram of a conversion block selector (CBS).  
     
    
     DETAILED DESCRIPTION  
       [0018]     The invention can be implemented in numerous ways, including as a process, an apparatus, a system, a composition of matter, a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention.  
         [0019]     A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.  
         [0020]     Reference will now be made in detail to one or more preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to the same or like parts. For the purpose of example, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention. The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in details so that the present invention is not unnecessarily obscured.  
         [0021]     Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and equivalents. Accordingly, it is intended that the scope of the invention be defined by the following Claims and their equivalents.  
         [0022]     The information-bearing signals described herein are time-varying. Representations of such a signal, such as by a voltage or a current, may additionally comprise a substantially constant component that does not convey information. These constituents of a signal may be described as AC and DC signal components, respectively. Reference may also be made to DC operating points, or operating conditions, of a circuit, system, or method, to describe conditions that remain substantially constant over time. Many time-varying signals may be instantiated as differential signals, having both a positive and negative component.  
         [0023]     The following table provides explanation for selected exemplary block and signal names used herein. Where convenient, similar names with varying suffixes may be used to refer to blocks or signals with the same or like functionality.  
                                       BLOCK           GCM   gain controlled mixer       GBC   gain block cell       CBS   conversion block selector       GCB   gain conversion block       GCBP   gain conversion block pair       PGCB   positive gain conversion block       NGCB   negative gain conversion block       QPGCB   portion of a PGCB that processes quadrature (Q) input           signal components       QNGCB   portion of a NGCB that processes quadrature (Q) input           signal components       IPGCB   portion of a PGCB that processes in-phase (I) input           signal components       INGCB   portion of a NGCB that processes in-phase (I) input           signal components       SIGNAL       LO   local oscillator       LOni, LOpi   local oscillator, differential pair(negative, positive),           I component       LOnq, LOpq   local oscillator, differential pair (negative, positive),           Q component       ini, ipi   input, differential pair (negative, positive), I component       inq, ipq   input, differential pair (negative, positive), Q component       On, Op   output, differential pair (negative, positive)       CWI   control word input                  
 
         [0024]      FIG. 1  is a block diagram of a gain controlled mixer GCM  100 . By way of example and not limitation, GCM  100  receives input signals local oscillator (LO)  141 , and baseband (BB)  142 , and GCM  100  provides output signal mixer output (MO)  143 . Each of the gain block cells GBC 1   111  through GBCn  113  provide both a mixing function between the input signals and a controllable gain upon the mixed result. Outputs of the gain block cells are received and combined by a summing node  150 . The summing node  150  provides an output signal of the GCM  100 , mixer output (MO)  143 .  
         [0025]     Within each gain block cell, there are one or more positive gain conversion blocks (PGCB) and one or more negative gain conversion blocks (NGCB). Each PGCB and NGCB provides combined mixing and gain functions. Each of the PGCB and NGCB within a gain block cell may be selectively enabled. An enabled PGCB provides gain of opposite polarity to the gain provided by an enabled NGCB.  
         [0026]     In  FIG. 1 , GBC 1   111  comprises positive gain block cells PGCB 1   121  through PGCBn  128 , and negative gain block cells NGCB 1   131  through NGCBn  138 . Each of the positive and negative gain block cells in GBC 1  is selectively enabled. Conversion block selector CBS 1   111  provides individual GCB enable signals to each of the positive gain conversion blocks and negative gain conversion blocks within GBC 1 . Similarly, CBS 2   112  provides GCB enable signals to positive gain block cells and negative gain block cells within GBC 2 , and CBSn  113  similarly provides for GBCn  103 . Each CBS provides a mapping that enables particular combinations of PGCB and NGCB in response to a control word input. Advantageously, a selectable “power-down” state may be provided, in which all of the PGCB and NGCB in each GBC, hence the entire GCM, are contemporaneously disabled, thus reducing circuit power consumption.  
         [0027]     In this embodiment, conversion block selectors CBS 1   111  through CBSn  113  are connected one to each corresponding GBC. In other embodiments, conversion block selectors may number greater or lesser than the number of gain block cells, and, individual conversion block selectors may be connected to one or more gain block cells.  
         [0028]     Embodiments of GCM  100  may comprise one or more gain block cells, as indicated by ellipses located on the figure between GBC 2   102  and GBCn  103 .  
         [0029]     In providing an output, the summing node  150  may give equal weighting to its inputs, that is, the GBC outputs it receives. In some embodiments, summing node  150  is simply an interconnection amongst GBCs  101 - 103 , receiving signal current contributions from each GBC.  
         [0030]     Embodiments of individual gain block cells may comprise one or more positive gain conversion blocks and one or more negative gain conversion blocks, as indicated by ellipses located on the figure between PGCB 2   122  and PGCBn  128 , and, between NGCB 2   128  and NGCBn  138 , respectively.  
         [0031]     Notably, the use of the index “n” following any of PGCB, NGCB, GBC or CBS illustrates that among each designator, a variable number of elements may be instantiated and not that the number of instantiations of each element is necessarily the same.  
         [0032]     In  FIG. 2 , a block diagram of a gain block cell GBC  200  comprising a plurality of gain conversion block pairs (GCBPs) coupled to a conversion block selector CBS  210  is shown. Each gain conversion block pair GCBP  220 - 227  is formed by the combination of a PGCB and a NGCB. It should be appreciated that this structure accommodates an illustrative embodiment shown here comprising eight GCBPs, GCBP 0   220  through GCBP 7   227 . By way of example and not limitation, each GCBP receives common LO and baseband differential input signals. Outputs of each of the GCBPs  220 - 227  are summed together, in a common summing node  230 . Common summing node  230  may simply be an interconnection amongst GCBPs  220 - 227 , receiving signal current contributions from each. Each GCBP  220 - 227  receives distinct control signals that separately enable the positive gain conversion block and the negative gain conversion block within each GCBP  220 - 227 . That is, the “nth” GCBP receives GBC enable signals pos&lt;n&gt; and neg&lt;n&gt; respectively, for n=(0,1,2, . . . ,7). These signals are provided by conversion block selector CBS  210 , in response to a control word input CWI  211 . GBC  220  mixes a local oscillator LO signal input with a baseband signal input and provides selectable gain for the resultant output signal provided by common summing node  230 .  
         [0033]     In one embodiment, each of the LO and baseband input signals comprise input signal differential pairs separately for I and Q components, and the GBC output is a differential current pair, as shown and described further in  FIGS. 3A, 3B , and  3 C.  
         [0034]     The CBS  210  provides a decoding function for the control word input CWI  211 . In one embodiment the decoding may be trivially implemented as a register, wherein the CBS  210  outputs are bit-wise equivalents of the control word input CWI  211 . In other embodiments, the CBS  210  may be implemented with a look-up table function. A power-down state for the GBC  200  may be achieved in one or more of the selectable output states of the CBS  210 , wherein every one of the positive and negative gain conversion blocks within each GCBP  220 - 227  are disabled. This power-down state advantageously reduces power consumed by the CMOS transceiver. A power-down state for the GBC  200  shown in  FIG. 2  is achieved by means of the CBS  210  outputs contemporaneously disabling all of the GCB enable signals to the PGCB and the NGCB within every gain conversion block pair GCBP  220 - 227 .  
         [0035]     In one embodiment of the GBC  200 , the selectable positive and negative gains available from each GCBP are substantially equal in magnitude, that is, the absolute value of the gains are substantially matched. To further explain by example, within each GCBP  220 - 227  as further shown and described in  FIG. 3A , the circuit elements of PGCB  330  can, in one embodiment, each be substantially matched by the circuit elements of NGCB  331 . The LO and baseband input signals are in common to PGCB  330  and NGCB  331 . The gain conversion blocks  310 ,  311 ,  320 , and  321  comprise similarly disposed electrical circuit elements that process distinct input signals. As a consequence, for a given set of LO and baseband signal inputs to the GCBP  220 , the magnitude of the output signal produced under the condition of positive gain enabled (pos&lt;n&gt;=Vdd, neg&lt;n&gt;=0) is substantially equal to the magnitude of the output signal produced under the condition of negative gain enabled (pos&lt;n&gt;=0, neg&lt;n&gt;=Vdd).  
         [0036]     Referring again to  FIG. 2 , in one embodiment of the GBC  200 , within each of the GCBPs GCBP 0   220  through GCBP  227 , the PGCB and NGCB are well-matched to each other. Furthermore each of the PGCB and NGCB within each GCBP are well-matched to each other as a consequence of substantially matched circuit elements and topology, and common input signals. Thus, for this embodiment, maximum positive gain for this GBC  200  will result from contemporaneously enabling each PGCB within each of the GCBPs  220 - 227 , and that this resulting maximum positive gain is approximately equal to eight times the positive gain resulting from the enablement of a single PGCB. Similarly, the maximum negative gain for GBC  200  will result from enabling each NGCB within each of the GCBPs  220 - 227  shown and this resulting maximum negative gain is approximately equal to eight times the negative gain resulting from the enablement of a single NGCB. The magnitude of the maximum positive gain is substantially equal to the magnitude of the maximum negative gain in this embodiment.  
         [0037]     To more readily illustrate the process of gain selection, the term “x” is herein defined as the unit of gain provided in this embodiment by a single positive gain conversion block.  
         [0038]     It is possible to generate, by means of the CBS decoding function  210 , control states for GBC  220  gains that range from 8x to −8x, in controllable steps of 1x, in addition to a power down state that is both equivalent to 0x and disables each PGCB and NGCB.  
         [0039]     Negative gains may be useful, for example, in the transmit chain of a transceiver for driving a phased antenna array or in the receive chain for selecting signal polarities for baseband signal processing.  
         [0040]     Improved gain control accuracy may advantageously be obtained by using gain cancellation to produce gain values intermediate to the maximum positive and negative gains for GCB  200 . Referring again to GCBP 0   220  through GCBP 7   227  as shown and described in  FIG. 2 , it is notable that the DC operating points for current source inputs and outputs are substantially the same under the condition of positive gain enablement (pos&lt;n&gt;=Vdd, neg&lt;n&gt;=0) and negative gain enablement (pos&lt;n&gt;=0, neg&lt;n&gt;=Vdd). By maintaining a single enabled positive or negative conversion block in each GCBP  220 - 227 , the aggregate of circuit DC operating points are held substantially constant across changes in overall GBC  200  gain.  
         [0041]     By maintaining a single enabled positive or negative conversion block in each GCBP  220 - 227 , effective gain cancellation occurs when one or more positive gain conversion blocks are enabled within selected ones of GCBPs  220 - 227 , while one or more negative gain conversion blocks are enabled in other selected ones of GCBPs  220 - 227 . To a substantial extent, GCBPs enabled for opposite gain polarities “cancel each other out” with respect to AC gain, resulting in a net gain contribution for the GBC  220  that is equivalent to the difference between the number of positive and negative gain conversion blocks that are enabled.  
         [0042]     For example, a net gain of 4x may be obtained by enabling 6 PGCB (in 6 of GCBPs  220 - 227 ) while enabling 2 NGCB (in the 2 remaining of GCBPs  220 - 227 ). This has the desirable feature of maintaining consistent DC operating points within the overall GBC  220  circuit, which further contributes to the substantial gain matching over various gain settings and between portions of the circuitry.  
         [0043]     When using this gain cancellation technique to set specific GBC gain levels, the range of (+8x to −8x) still obtains, but the step size is now 2x.  
         [0044]     In  FIG. 3A , a positive gain conversion block PGCB  320  and negative gain conversion block NGCB  321  are shown, together forming a gain conversion block pair GCBP  220 . PGCB  320  comprises a portion responsible for processing I component inputs, IPGCB  310 , and, a portion responsible for processing Q component inputs, QPGCB  320 . Similarly, NGCB  331  comprises INGCB  311  and QNGCB  321 .  
         [0045]     In some embodiments a GCBP  220  may provide processing for one of I input or Q input processing, but not both. By way of example and not limitation, gain conversion block pairs are shown in  FIGS. 3B and 3C  that provide solely I input and solely Q input processing, respectively. In  FIG. 3B , IGCBP  350  comprises PGCB  310  and NGCB  311 . As  FIG. 3B  shows, PGCB  310  comprises only a portion for processing I inputs. This portion of this PGCB, which may be called an IPGCB, is thus identical to an entire PGCB  350  in GCBP  220 . Hence we have labeled the circuit  310  (I)PGCB in the figure to emphasize that it may be either an IPGCB or a PGCB in this case. The NGCB is correspondingly labeled (I)NGCB  311 , as it may be either an INGCB or a NGCB.  
         [0046]     The QGCBP  360  of  FIG. 3C  comprises PGCB  320  and NGCB  321 . These gain conversion blocks comprise only portions for processing Q inputs, in this embodiment. Hence they are labeled (Q)PGCB and (Q)NGCB, because PGCB  320  may be either a PGCB or a QPGCB, and, NGCB  321  may be either a NGCB or a QNGCB, according to the notation used herein.  
         [0047]     The electrical circuit elements making up each of the positive and negative gain conversion blocks in  FIG. 3A  are substantially the same. It can also be appreciated that the circuit elements used for processing the in-phase (I) differential current signals for baseband input and local oscillator (LO) input, as shown in  FIG. 3B  (I)PGCB  310  and (I)NGCB  311 , are substantially the same as the elements used for processing the quadrature (Q) differential current signals for baseband input and local oscillator input, as shown in  FIG. 3C  (Q)PGCB  320  and (Q)PGCB  321 . Notably,  310 ,  311 ,  320 , and  321  comprise similarly disposed electrical circuit elements that process distinct input signals.  
         [0048]     GCBP  220  mixes the local oscillator (LO) signal input with the baseband signal input and provides selectable gain for the resultant output signal. The GCB enable signals pos and neg selectively enable corresponding positive and negative gain conversion blocks, resulting in a positive or negative gain contribution, respectively, in the signal path. Essentially zero gain is contributed when neither pos nor neg are enabled. In some embodiments, essentially zero gain may also be contributed upon enabling both pos and neg, as taught further herinafter.  
         [0049]     The baseband input signal input may comprise both in-phase (I) and quadrature (Q) differential current inputs, shown here as ipi, ini, and ipq, inq, respectively. The local oscillator (LO) input may comprise both in-phase (I) and quadrature (Q) differential voltage inputs, shown here as LOpi, LOni and LOpq, LOnq, respectively. The output signal comprises a single instance of differential current outputs, shown here as Op, On. The output signal is a result of summing output currents from the circuits each of IPGCB  310 , INGCB  311 , QPGCB  320 , and QNGCB  321 .  
         [0050]     In order to illustrate in further detail the mixing circuit function, first consider the portion of this circuitry providing positive gain to the mix of in-phase (I) differential components of the input and LO signals. These elements are shown in (I)PGCB  310  in  FIG. 3B .  
         [0051]     When each of the NMOS transistors  361 ,  362 ,  363 , and  364  are enabled, each of their drain current AC-component signal outputs represents a mix, or product, of their AC-component gate voltage signal and their AC-component source current signal inputs. The transistors are enabled by a DC voltage bias when the pos signal is at a high logic level, that is, when pos is at a voltage substantially equal to Vdd.  
         [0052]     When pos is at a low logic level, that is, when pos is at a voltage substantially equal to 0V or logic ground, these transistors are disabled, whereupon their drain current AC output signal is essentially zero and does not contribute significantly to the AC output current of the overall circuit.  
         [0053]     The AC voltage signal at the gate of transistors  361  and  364  represents the AC voltage signal input provided by the positive member of the differential input pair of the local oscillator, LOpi. The AC input voltage is coupled to the gate AC voltage by the C  372 . Similarly, the AC voltage signal at the gate of transistors  362  and  363  represents the AC voltage signal input provided by the negative member of the differential input pair of the local oscillator, LOni, which has been coupled to the gate AC voltage by C  382 .  
         [0054]     The AC source current signal at the drain of transistors  363  and  364  is provided by the positive member of the differential input pair of the baseband input, ipi. The AC source current signal at the drain of transistors  361  and  362  is similarly provided by the negative member of the differential input pair of the baseband input, ini.  
         [0055]     The LO in-phase I component differential voltage inputs result in differential voltage inputs to the gates of transistors  363  and  364 . To the extent that the LO input differential input members&#39; AC components are complementary, that is, substantially equal and opposite, the gate-source voltages on  363  and  364  are also equal and opposite. Current flowing from the common source connection is effectively steered at any moment to the drain of one of  363  and  364 , resulting in a consistent operating point for the current source ipi.  
         [0056]     The output signal from each of the enabled transistors  361 ,  362 ,  363 , and  364  results from mixing two AC signal inputs. The drain current AC signal output of  364  corresponds to mixing the AC signal present on the positive member of the LO differential input, LOpi, with the AC signal present on the positive member of the baseband input, ipi. The drain current of  364  is summed into the positive member of the differential output of this circuit, Op. Output contributions resulting from mixing like signs of input members contribute to the positive member of the differential circuit output, and output contributions resulting from mixing different signs contribute to the negative member of the differential circuit output. Thus  362  output, resulting from a mix of two negative members, LOni and ini, contributes to Op. The outputs of  361  and  363 , both resulting from mixing a combination of positive and negative members ( (LOpi,ini) and (LOni, ipi) respectively), are summed into On.  
         [0057]     As described above, a positive gain from the mix of in-phase (I) components of the input signals may be obtained by means of (I)PGCB  310  in  FIG. 3B . The positive gain is selectively enabled by means of a pos GCB enable signal.  
         [0058]     (I)NGCB  311  provides negative gain from the mix of in-phase (I) components of the input signals, is shown as  311  in  FIG. 3B . The negative gain is selectively enabled by means of a neg GCB enable signal.  
         [0059]     As is further illustrated in  FIG. 3B , the circuit elements and topology (I)NGCB  311  are notably similar to (I)PGCB  310 , described above. (I)NGCB  311  may be briefly described as an instantiation of (I)PGCB  310  with the following differences:  
         [0060]     Gain is selectively enabled by means of the neg signal.  
         [0061]     The drain current outputs of the transistors are summed to the positive and negative members of the differential output with the opposite sense to that described for the (I)PGCB,  310 . That is, (I)NGCB  311 , different-sign contributions are directed to Op, and like-sign contributions are directed to On. Output contributions resulting from mixing like signs of input members contribute to the negative member of the differential circuit output, and output contributions resulting from mixing different signs contribute to the negative member of the differential circuit output.  
         [0062]     A PGCB  330  is shown in  FIG. 3A , with processing for both in-phase (I) and quadrature (Q) input signal components provided by IPGCB  310  and QPGCB  320 . It provides positive gain for the mix of in-phase (I) components of the input signals, and negative gain for the mix of quadrature (Q) components of the input signals. The gain is selectively enabled by means of a pos GCB enable signal.  
         [0063]     Note that, for QPGCB  320 , the drain current outputs of the transistors are summed to the positive and negative members of the differential output with the opposite sense to that described for the IPGCB  310 . For QPGCB  320 , different-sign contributions are directed to Op, and like-sign contributions are directed to On. Output contributions resulting from mixing like signs of input signals contribute to the negative member of the differential circuit output, and output contributions resulting from mixing different signs contribute to the positive member of the differential circuit output.  
         [0064]     In  FIG. 3A , NGCB  331  includes circuitry for processing both in-phase ( 1 ) and quadrature (Q) input signal components, corresponding to INGCB  311  and QNGCB  321 . It provides negative gain for the mix of in-phase (I) components of the input signals, and positive gain for the mix of quadrature (Q) components of the input signals. The gain is selectively enabled by means of the neg GCB enable signal.  
         [0065]     Note that, for the Q portion QNGCB  321  of this NGCB  331 , the drain current outputs of the transistors are summed to the positive and negative members of the differential output with the opposite sense to that described for the I portion, INGCB  311 .  
         [0066]     That is, for the NGCB circuit in  321 , like-sign contributions are directed to Op, and different-sign contributions are directed to On. Output contributions resulting from mixing like signs of input members contribute to the positive member of the differential circuit output, and output contributions resulting from mixing different signs contribute to the negative member of the differential circuit output.  
         [0067]     In the description of PGCB  330  and NGCB  331  that include both I and Q component processing, positive gain conversion blocks supply positive gain for the mix of I components, but negative gain for the mix of Q components, and negative gain conversion blocks supply negative gain for the mix of I components, but positive gain for the mix of Q components. This treatment of Q component polarities is intentional, and advantageous for some signal processing functions that may be accomplished within a transceiver, such as sideband suppression in modulation and demodulation schemes. For the present invention, the descriptions herein will describe the combination of I and Q gain results selectively enabled in a PGCB as “positive gain” and the gain results selectively enabled in a NGCB as “negative gain”, notwithstanding the details of the relative polarity of I and Q portions and components within each PGCB and NGCB.  
         [0068]     It is notable that circuits IPGCB  310 , QPGCB  311 , INGCB  320 , and QNGCB  321  comprise similarly disposed electrical circuit elements that process distinct input signals. In some embodiments, the properties of elements within these circuits may be very substantially matched. For example, within and between these circuits, the transistors, resistors, capacitors, and connections between elements may be instantiated in a CMOS circuit with substantially similar geometry and other physical characteristics. Notably, the degree to which circuit element properties match within a CMOS implementation is highly dependent upon geometry, and significantly independent of manufacturing process and temperature variation. Consequently, a CMOS embodiment that includes multiple instantiations of IPGCB  310 , QPGCB  311 , INGCB  320 , and QNGCB  321  may have substantially similar mixing and gain performance between like circuits as a consequence of instantiations having substantially similarly matched circuit elements. For example, a CMOS embodiment may advantageously provide a substantially similar output signal, in terms of resultant gain and mix, from a first instantiation of IPGCB  310  and a second instantiation of IPGCB  310 , under the conditions that both instantiations are provided substantially similar inputs.  
         [0069]      FIG. 7  illustrates a logic decoder embodiment of a CBS  210 , in a condensed schematic form. The circuit includes eight instantiations of the logic gates shown. Signal names that are indexed in this representation straightforwardly correspond to the eight indexed instantiations. A control word input  211  comprising gIF&lt; 0 &gt;, gIF&lt; 1 &gt;, and pwd is decoded by logic gates, producing control signals pos&lt; 7 : 0 &gt;  820  and neg&lt; 7 : 0 &gt;  825 . The resulting control signals are appropriate as GBC enable signals for GCBPs  220 - 227 , as illustrated in  FIG. 2 . Typically, pos&lt; 0 &gt; and neg&lt; 0 &gt; serve as GBC enable signals for a first PGCB and a first NGCB within a first GCBP, respectively. pos&lt; 1 &gt; and neg&lt; 1 &gt; serve as GBC enable signals for a second PGCB and a second NGCB within a second GCBP, respectively, and so on. Note that when the pwd 810 input signal is enabled, it results in a “power down” state, regardless of the logical state of the other inputs. Also note that this CBS implements gain cancellation. As shown in the table following, this CBS in combination with a GBC  200  as illustrated and described in  FIG. 2  provides for selectable gains of 2x, 4x, 6x, and 8x, and, a power-down state with essentially zero gain. In the table, logic states are shown for input signals, along with corresponding counts of enabled PGCBs and NGCBs, and a resulting gain contribution for the GBC that is controlled by the CBS.  
                                                               PGCB   NGCB                       enabled   enabled   GBC       pwd   gIF&lt;0&gt;   gIF&lt;1&gt;   (count)   (count)   gain                   0   0   0   5   3   2×       0   0   1   6   2   4×       0   1   0   7   1   6×       0   1   1   8   0   8×       1   (don&#39;t care)   (don&#39;t care)   0   0   power-down                    
         [0070]      FIG. 4  is a block diagram of a dual-conversion gain controlled mixer (GCM) comprising a first conversion stage  510  and a second conversion stage  560 . The first conversion stage provides mixing of baseband  511  and first local oscillator (LO&lt; 1 &gt;)  512  input signals. In some embodiments the first conversion stage also provides controllable gain by means of gain conversion blocks within, the gain conversion blocks being enabled by one or more related conversion block selectors.  
         [0071]     The second conversion stage  560  receives as input signals the output of the first conversion stage IF  561 , and, a second local oscillator LO&lt; 2 &gt;  562 . The second conversion stage provides mixing of these input signals. In some embodiments the second conversion stage also provides controllable gain by means of gain conversion blocks within, that are enabled by one or more conversion block selectors.  
         [0072]     In some embodiments, the input and output signals may each comprise both in-phase (I) and quadrature (Q) signal components.  
         [0073]      FIG. 5  illustrates, in schematic form, one embodiment of a gain controlled mixer having both a first and a second conversion stage.  
         [0074]     The first conversion stage, comprising Gilbert Cell mixers  610  and  620 , provides mixing of the baseband  612  and first local oscillator LO&lt; 1 &gt;  611  input signals.  
         [0075]     The second conversion stage receives as input signals the output of the first conversion stage IF  642 , and, a second local oscillator LO&lt; 2 &gt;  641 . The second conversion stage provides mixing and gain functions in gain block cell GBC  640 . A conversion block selector CBS  210  provides a control state for GBC  640 , expressed as the logic levels present on GCB enable signals neg&lt; 0 : 7 &gt; and pos&lt; 0 : 7 &gt;, that are received as GBC  640  inputs. A control state may be distinctly selected from a plurality of available states, including a plurality of gain selections and a power down state. CBS  210  provides a mapping or decoding function, mapping values of the control word input CWI  211  to specific logic levels for the pos&lt; 0 : 7 &gt; and neg&lt; 0 : 7 &gt; GBC enable signal outputs.  
         [0076]     The signal output of this gain controlled mixer is represented as differential current outputs Op and On of GBC  640 . Note that in this embodiment, a load network  645  has been provided to convert the AC current outputs to voltage representations. The load network  645  may comprise lossy inductors, in some embodiments.  
         [0077]     Current source bias circuits within IBIAS  630  provide DC bias currents to the IF  642  circuit nodes. These provided DC bias currents reduce the DC current flowing through the IF signal inputs, labeled ini, ipi, inq, ipq in GBC  640 . The reduced input DC current provides an improved operating condition for the (positive and negative) gain conversion blocks within GBC  640 , allowing for relatively larger gain capability than would otherwise be the case. The reduced DC current requirements may advantageously enhance the linearity of the gain conversion blocks and reduce the drive requirement for the local oscillator inputs LO&lt; 2 &gt;  641 .  
         [0078]     The first conversion stage input signal baseband  612  comprises differential current pairs conveying in-phase (I) and quadrature (Q) signal components. The similarly-labeled individual baseband input signals received at the inputs of Gilbert Cell mixers  610  and  620  are substantially identical. For example, the ini1 and ini2 elements of baseband  612  may be provided by the outputs of distinct current drivers receiving the same signal input. Note the opposing polarity of Q component inputs provided to the Gilbert Cell mixers  610  and  620  in  FIG. 5 .  
         [0079]     The first conversion stage input signal LO&lt; 1 &gt;  611  comprises differential voltage signal pairs conveying I and Q signal components, as is shown in  FIG. 5 . Note that Gilbert Cell mixer  620  receives input components I and Q transposed relative to Gilbert Cell mixer  610 .  
         [0080]     Outputs of the first conversion stage IF  642  comprise I and Q components as shown in  FIG. 5 . These signals are represented with differential current signal pairs.  
         [0081]     The second conversion stage input signal LO&lt; 2 &gt;  641  comprises differential voltage signal pairs conveying I and Q signal components, as is shown in  FIG. 5 .  
         [0082]     The output of the second conversion stage, the differential current pair On and Op of gain block cell GBC  640 , comprise an I (in-phase) component.  
         [0083]      FIG. 6  illustrates, in a simplified schematic diagram, a current source bias circuit disposed between first and second conversion stages in a gain controlled mixer. Elements of the first conversion stage are shown within  710 . Elements of the second conversion stage are shown within  730 . These elements are common to embodiments of conversion stages that perform a mixing function, that is, mixers, including (positive and negative) gain conversion blocks, as well as Gilbert Cell mixers. In order to reduce the amount of DC current that flows into the second conversion stage mixers, current sources have been provided as shown in  FIG. 6 . Reducing the amount of DC current that flows into the second conversion stage mixers may advantageously enhance the linearity, and, reduce the amount of LO drive required for the second conversion stage mixers.  
         [0084]     One element of the first conversion stage output is a DC current sink  712  of  21  units, shown in  FIG. 6 . A DC current source bias circuit  720  provides Ibias units of current towards the 2I unit current requirement of  712 . The DC current source requirement at the second conversion stage input  731  is thereby reduced from 2I to (2I-Ibias) by the presence of the bias current source  720 .  
         [0085]      FIG. 6  illustrates that circuit elements of the first and second conversion stages may be disposed in a cascode configuration.  
         [0086]     Accordingly, it is intended that the scope of the invention be defined by the following Claims and their equivalents.  
         [0087]     Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.