Abstract:
An electronic device comprises an input transmission line that receives an input signal, an output transmission line that transmits an output signal, a local oscillator transmission line that transmits a local oscillator signal, multiple amplification and mixing stages arranged in parallel between the input and output transmission lines and each amplifying a received portion of the input signal and mixing the amplified portion of the input signal with the local oscillator signal to produce a portion of the output signal, and multiple amplification stages arranged in parallel between the input and output transmission lines and each amplifying a received portion of the input signal to produce a portion of the output signal. The amplification stages are located proximate an output side of the electronic device, and the amplification and mixing stages are located proximate an input side of the electronic device.

Description:
BACKGROUND 
       [0001]    Mixers and samplers can be found in most high frequency communication systems. For example, mixers are commonly used to shift signals from one frequency range to another for convenience or compatibility in transmission or signal processing. Samplers, on the other hand, are generally used to convert continuous signals into discrete signals for signal processing. 
         [0002]    The performance of a mixer or sampler can be evaluated according to parameters such as bandwidth, noise, and gain, among others. As information rates go up, the bandwidths of the underlying components like mixers and samplers must also increase. Similarly, adequate noise and/or gain values are required to maintain quality of the processed information. Each of these parameters is important for most modern systems, as developers are continually pushing the envelope of processing speed and quality. 
         [0003]    In high frequency mixers and samplers, bandwidth, noise and gain are sensitive to intrinsic device characteristics and parasitics. In addition there are tradeoffs to be made between these parameters. It is difficult in general to improve one without sacrificing the other two. One technique for optimizing these parameters is by distributing the devices along a transmission line. A basic implementation of this technique can be found in a travelling wave amplifier. 
         [0004]    In addition as a consequence of this strong sensitivity to device parasitics, high frequency mixers and samplers are commonly implemented with specialized devices or processes that minimize or reduce parasitics. For example, some mixers or samplers may be implemented with pseudomorphic high electron mobility transistors (pHEMT), which tend to have relatively low parasitic C. Similarly, some mixers may be manufactured by forming a mixer bridge with specialized processes typically used to manufacture tow capacitance diodes. 
         [0005]    Unfortunately, these specialized devices and processes are generally expensive and inefficient to manufacture. Consequently, there is a general need for improved designs for high performance mixers and samplers. 
       SUMMARY 
       [0006]    In a representative embodiment, an electronic device comprises an input transmission line configured to receive an input signal, an output transmission line configured to transmit an output signal produced according to the input signal, a local oscillator transmission line configured to transmit a local oscillator signal, a plurality of amplification and mixing stages arranged in parallel between the input and output transmission lines and each configured to amplify a received portion of the input signal and mix the amplified portion of the input signal with the local oscillator signal to produce a portion of the output signal, and a plurality of amplification stages arranged in parallel between the input and output transmission lines and each configured to amplify a received portion of the input signal to produce a portion of the output signal, wherein the plurality of amplification stages are located proximate an output side of the electronic device that transmits the output signal, and the plurality of amplification and mixing stages are located proximate an input side of the electronic device that receives the input 
         [0007]    In certain related embodiments, the electronic device further comprises an additional output transmission line configured to transmit an additional output signal produced according to the input signal, wherein the output signal corresponds to even samples of a synthetic sampler and the additional output signal corresponds to odd samples of a synthetic sampler, an additional plurality of amplification and mixing stages arranged in parallel between the input transmission line and the additional output transmission line and each configured to amplify a received portion of the input signal and mix the amplified portion of the input signal with the local oscillator signal to produce a portion of the additional output signal, and an additional plurality of amplification stages arranged in parallel between the input transmission line and the additional output transmission line and each configured to amplify a received portion of the input signal to produce a portion of the additional output signal, wherein the additional plurality of amplification stages are located proximate the output side of the electronic device that transmits the output signal, and the additional plurality of amplification and mixing stages are located proximate the input side of the electronic device that receives the input signal. 
         [0008]    In certain related embodiments, the electronic device further comprises one or more first transmission line elements each disposed along the input transmission line between a corresponding pair of the amplification and mixing stages, one or more second transmission line elements each disposed along the output transmission line between a corresponding pair of the amplification and mixing stages, and one or more third transmission line elements each disposed along the local oscillator transmission line between a corresponding pair of the amplification and mixing stages. Each of the first through third transmission line elements may comprise a circuit trace, for example. Moreover, the electronic device may further comprise one or more first transmission line elements each disposed along the input transmission line between a corresponding pair of the amplification stages, and one or more second transmission line elements each disposed along the second transmission line between a corresponding pair of the amplification stages. 
         [0009]    In another representative embodiment, an electronic device comprises an input transmission line configured to receive an input signal, an output transmission line configured to transmit an output signal produced according to the input signal, a sample clock transmission line configured to transmit a sample clock signal, and a plurality of amplification and sampling stages arranged in parallel between the input and output transmission lines and each configured to amplify a received portion of the input signal and sample the amplified portion of the input signal using the sample clock signal to produce a portion of the output signal. 
         [0010]    In certain related embodiments, the electronic device further comprises an additional output transmission line configured to transmit an additional output signal produced according to the input signal, wherein the output signal corresponds to even samples of the input signal and the additional output signal corresponds to odd samples of the input signal. 
     
    
     
       BRET DESCRIPTION OF THE DRAWINGS 
         [0011]    The described embodiments are best understood from the following detailed description when read with the accompanying drawing figures. Wherever applicable and practical, like reference numerals refer to like elements. 
           [0012]      FIG. 1  is a circuit diagram illustrating a traveling wave mixer, in accordance with a representative embodiment. 
           [0013]      FIG. 2  is a circuit diagram illustrating an amplification and mixing (A/M) stage, in accordance with a representative embodiment. 
           [0014]      FIG. 3  is a circuit diagram illustrating a traveling wave synthetic sampler, in accordance with a representative embodiment. 
           [0015]      FIG. 4  is a circuit diagram illustrating an amplification and sampling (A/S) stage, in accordance with a representative embodiment. 
           [0016]      FIG. 5  is a circuit diagram illustrating a traveling wave synthetic sampler, in accordance with a representative embodiment. 
           [0017]      FIG. 6A  is a block diagram of another traveling wave synthetic sampler, in accordance with a representative embodiment. 
           [0018]      FIG. 6B  is a circuit diagram of an input transmission line in the traveling wave synthetic sampler of  FIG. 6A , in accordance with a representative embodiment. 
           [0019]      FIG. 6C  is a circuit diagram of a local oscillator (LO) signal generation unit in the traveling wave synthetic sampler of  FIG. 6A , in accordance with a representative embodiment. 
           [0020]      FIG. 6D  is a circuit diagram of high band mixers in the traveling wave synthetic sampler of  FIG. 6A , in accordance with a representative embodiment. 
           [0021]      FIG. 6E  is a circuit diagram of low band amplifiers in the traveling wave synthetic sampler of  FIG. 6A , in accordance with a representative embodiment. 
           [0022]      FIG. 6F  is a circuit diagram of an odd sample combiner in the traveling wave synthetic sampler of  FIG. 6A , in accordance with a representative embodiment. 
           [0023]      FIG. 6G  is a circuit diagram of an even sample combiner in the traveling wave synthetic sampler of  FIG. 6A , in accordance with a representative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    In the following detailed description, for purposes of explanation and not limitation, representative embodiments disclosing specific details are set forth in order to provide a thorough understanding of the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparatuses and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparatuses are clearly within the scope of the present teachings. 
         [0025]    The terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. The defined terms are in addition to the technical and scientific meanings of the defined terms as commonly understood and accepted in the technical field of the present teachings. As used in the specification and appended claims, the terms ‘a’, ‘an’ and ‘the’ include both singular and plural referents, unless the context clearly dictates otherwise. Thus, for example, ‘a device’ includes one device and plural devices. 
         [0026]    The described embodiments relate generally to traveling wave mixers, samplers, and synthetic samplers. These devices can be implemented by arranging various components in parallel between an input transmission line and an output transmission line such that their functional properties (e.g., transconductance) are added linearly white parasitic properties, such as inductance and capacitance, are distributed along the transmission lines rather than lumped together at a single input or output point. For example, in a traveling wave mixer according to various embodiments, a plurality of A/M. stages are arranged in parallel between the input and output transmission lines, and a separate LO transmission line is connected to each of the AN. stages to provide an LO signal to be mixed with an input signal provided through the input transmission line. 
         [0027]    The described embodiments may provide various benefits compared to mixers and samplers formed of a single stage. For instance, the use of multiple stages to distribute parasitic properties along the transmission tines can increase the gain-bandwidth product and/or signal to noise ratio (SNR) for a particular bandwidth. It can also provide higher SNR and drive than a single stage amplifier and mixer for the same bandwidth. Moreover, it may make it easier to split an output signal to drive separate circuits, and it may allow for combination of mixers and amplifier stages with relatively precise time alignment. The above and other benefits may allow relatively high frequency (e.g., at a rate of 100 GHz or more) mixers or samplers to be manufactured using standard high frequency processes (e.g., silicon germanium (SiGe) and indium phosphide (InP)) instead of specialized pHEMT processes or specialized process used to manufacture low capacitance diodes. 
         [0028]    The described embodiments find ready application in various contexts in which high frequency signals are processed, such as computing systems, communication systems, and test and measurement systems, to name but a few. For example, a test instrument for RF devices may comprise a traveling wave mixer, sampler, or synthetic sampler as described below. 
         [0029]      FIG. 1  is a circuit diagram illustrating a traveling wave mixer  100 , in accordance with a representative embodiment. Like other mixers, traveling wave mixer  100  receives an input signal and an LO signal, and it produces a product of the input signal and the signal in the time domain. The input signal is typically a radio frequency (RF) signal, and the LO generally includes frequencies determined by a difference between frequencies of the input signal and the LO signal. 
         [0030]    Referring to  FIG. 1 , traveling wave mixer  100  comprises a first transmission line  105  (“input transmission line”), a second transmission line  115  (“Output transmission line”), a plurality of A/M stages arranged in parallel between first and second transmission lines  105  and  115 , and a third transmission line  110  (“LO transmission line”). The first through third transmission lines each comprise a plurality of transmission line elements, labeled “TL”. Each of the transmission line elements comprises a smaller transmission line and has a characteristic delay. Each of the A/M stages comprises a transconductance (gm) amplifier  135  arranged in series with a mixer  140 . 
         [0031]    Although drawn as single lines in  FIG. 1 , each of the transmission lines typically comprises a pair of conductors for differential signaling. For example, as illustrated in  FIG. 2 , the LO transmission line may comprise a positive signal line LOP for transmitting an LO signal with positive polarity, and a negative signal line LON for carrying the LO signal with negative polarity. Similarly, as also illustrated in  FIG. 2 , the input transmission line may comprise a positive RF line REP and a negative RF line RFN. 
         [0032]    First transmission line  105  is connected between an input port  120  (or terminal) and ground via a first plurality of transmission line elements and a first terminating resistor Rt. Second transmission line  115  is connected between an output port  130  and ground via a second plurality of transmission line elements and a second terminating resistor Rt. Third transmission line  110  is connected between an LO port and ground via a third plurality of transmission line elements and a third terminating resistor Rt. The transmission line elements typically take the form of circuit traces, such as those produced by known integrated circuit (IC) manufacturing processes, and their characteristic delays are determined, at least in part, by the properties of those circuit traces. The terminating resistors are included on the respective transmission lines to minimize destructive signal reflections. 
         [0033]    First transmission line  105  is configured to receive a first signal (“input signal” or “RF signal”) through input port  120 . Second transmission line  115  is configured to transmit a second signal (“output signal”), which is produced in relation to the first signal, through output port  130 . Third transmission line  110  is configured to supply an LO signal to the mixer of each of the plurality of A/M stages. Gm amplifiers  135  are configured to convert voltages apparent on first transmission line  105  into currents supplied to the respective mixers  140 . Mixers  140  are configured to mix the LO signal with the respective converted voltages. 
         [0034]    During typical operation, the input signal is supplied to input port  120  of first transmission line  105 . As the input signal propagates down first transmission line  105 , the individual A/M stages respond by inducing an amplified and frequency translated complementary forward traveling wave on second transmission line  115 . First and second transmission lines  105  and  115  are typically designed such that their transmission line elements produce substantially equal delay, which results in the respective outputs of the individual A/M stages summing in phase. The design of transmission line elements with substantially equal delays can be accomplished through proper selection of propagation constants and lengths of the two lines. 
         [0035]    The overall gain of traveling wave mixer  100  is generally a linear function of the number of A/M stages, exhibiting an additive gain with an increasing number of stages. More specifically, traveling wave mixer  100  exhibits an additive gain with an increasing number of stages. This additive gain, coupled with the distribution of parasitics across the transmission lines, enables traveling wave mixer  100  to achieve an increased gain-bandwidth product while maintaining a desired SNR. 
         [0036]      FIG. 2  is a circuit diagram illustrating an A/M stage  200 , in accordance with representative embodiment. A/M stage  200  represents one possible implementation of an A/M stage formed by one of gm amplifiers  135  and one of mixers  140 . Although the illustrated A/M stage is constructed with bipolar-junction transistors (BJTs), those skilled in the art will recognize that a functionally similar or equivalent A/M stage could be constructed with other types of transistors, such as junction gate field effect transistors (JFETs) or metal oxide semiconductor field effect transistors (MOSFETs). 
         [0037]    Referring to  FIG. 2 , A/M stage  200  comprises a gm amplifier  235  and a mixer  240 , 
         [0038]    A/M stage  200  receives an input RF signal through a pair of differential signal lines connected to gm amplifier  235 , and it receives an LO signal through a pair of differential signal lines connected to mixer  240 . A/M stage  200  receives the RE signal with positive polarity through a positive RF line RFP, and it receives the RF signal with negative polarity through a negative RF line RFN. A/M stage  200  receives the LO signal with positive polarity through a positive LO line LOP, and it receives the LO signal with negative polarity through a negative LO line LON. 
         [0039]    Gm amplifier  235  comprises a pair of BJTs  205  and  210 , each arranged in an amplifying configuration. BJT  205  receives the RF signal with positive polarity at its base, and BJT  210  receives the RF signal with negative polarity at its base. Gm amplifier  235  further comprises a pair of resistors R 1  and R 2  and a capacitor C 1  arranged between the respective emitters of BJTs  205  and  210  and a current source ICS, as illustrated in the drawing. 
         [0040]    Mixer  240  is a Gilbert mixer comprising two cross coupled differential pairs of transistors. In particular, it comprises a first pair of emitter-connected BJTs  215  and  220 , and a second pair of emitter-connected BJTs  225  and  230 . The respective emitters of the first pair are connected to the collector of BJT  205 , and the respective emitters of the second pair are connected to the collector of BJT  210 . The respective bases of BJTs  215  and  230  receive the LO signal with positive polarity through positive LO line LOP, and the respective bases of BJTs  220  and  225  receive the signal with negative polarity through negative LO line LON. The positive and negative LO lines LOP and LON are connected to a positive supply voltage Vcc through corresponding inductors L 1  and L 2 . 
         [0041]    The respective collectors of BJTs  215  and  225  are connected to a negative mixing output line IMixN, and the respective collectors of BJTs  220  and  230  are connected to a positive mixing output line IMixP. In the context of an electronic device such as that illustrated in  FIG. 1 , the positive and negative mixing output lines IMixP and IMixN of each A/M stage are typically connected to the output transmission line, which forms a system where the current outputs of the mixers are summed in phase. 
         [0042]      FIG. 3  is a circuit diagram illustrating a traveling wave sampler  300 , in accordance with a representative embodiment. Traveling wave sampler  300  is similar to traveling wave mixer  100 , except that mixers  140  are replaced with samplers  340 , and the LO signal is replaced with a sample clock signal. The combination of each gm amplifier  135  and a corresponding sampler  340  constitutes an amplification and sampling (A/S) stage. The operation of traveling wave sampler  300  can be understood generally by analogy with the description of  FIG. 1 . The operation of the A/S stages, in particular, can be understood from the description of  FIG. 4  below. 
         [0043]      FIG. 4  is a circuit diagram illustrating A/S stage  400 , in accordance with a representative embodiment. A/S stage  400  represents one possible implementation of an A/M stage formed by one of gm amplifiers  135  and one of samplers  340 . 
         [0044]    Referring to  FIG. 4 , A/S stage  400  comprises a gm amplifier  435  and a sampler  440 . A/S stage  400  receives an input RF signal through a pair of differential signal lines connected to gm amplifier  435 , and it receives a sample clock signal through a pair of differential signal lines connected to sampler  440 . A/S stage  400  receives the RF signal with positive polarity through a positive RF line RFP, and it receives the RF signal with negative polarity through a negative RF line RFN. A/S stage  400  receives the sample clock signal with positive polarity through a positive sample clock line SCKP, and it receives the sample clock signal with negative polarity through a negative sample clock tine SCKN. 
         [0045]    Gm amplifier  435  has the same structure and function as gm amplifier  235  of  FIG. 2 . It comprises a pair of BJTs  405  and  410 , a pair of resistors RI and R 2 , and a capacitor C 1 , arranged in the same configuration as corresponding features in  FIG. 2 . 
         [0046]    Sampler  440  is similar to mixer  240 , except that its outputs are not cross coupled. The collectors of each sampler output go to a separate distributed tine. This produces an odd and even sample. The resulting samples have an aperture width of approximately ½ the sample clock period. More specifically, sampler  440  comprises a first pair of emitter-connected BJTs  415  and  420 , and a second pair of emitter-connected BJTs  425  and  430 . The respective emitters of the first pair are connected to the collector of BJT  405 , and the respective emitters of the second pair are connected to the collector of BJT  410 . The respective bases of BJTs  415  and  430  receive the sample clock signal with positive polarity through positive sample clock line SCKP, and the respective bases of BJTs  420  and  425  receive the sample clock signal with negative polarity through negative sample clock line SCKN. The positive and negative sample clock lines SCKP and SCKN are connected to a positive supply voltage Vcc through corresponding inductors L 1  and L 2 . 
         [0047]    The respective collectors of BJTs  415  through  430  are connected to sample output lines corresponding to even and odd samples of and positive and negative polarities. More specifically, the collector of BJT  415  is connected to a negative-polarity even sample output line ISEN, the collector of BJT  420  is connected to a negative-polarity odd sample output line ISON, the collector of BJT  425  is connected to a positive-polarity odd sample output line ISOP, and the collector of BJT  430  is connected to a positive-polarity even sample output line ISEP. In the context of an electronic device such as that illustrated in  FIG. 1 , the output lines ISEN, ISON, ISOP, and ISEP of each A/M stage are typically connected to the output transmission line, which forms a system where the current outputs of the samplers are summed in phase. 
         [0048]      FIG. 5  is a circuit diagram illustrating a traveling wave synthetic sampler  500 , in accordance with a representative embodiment, and  FIGS. 6A through 6G  are various diagrams illustrating another traveling wave synthetic sampler  600 , in accordance with a representative embodiment. 
         [0049]    Certain principles of synthetic sampling, as well as example technologies for performing synthetic sampling are described in U.S. patent application Ser. No. 13/097,882 filed Apr. 29, 2011, the subject matter of which is hereby incorporated by reference. In general, a synthetic sampler produces samples each comprising a combination of a mixed high band signal and an amplified low band signal. An even sample is equal to the high band signal plus the low band signal and an odd sample is equal to the high band signal minus the low band signal. A traveling wave design for synthetic sampling can perform synthetic sampling in a single stage while maintaining acceptable SNR. In addition the distributed nature of the traveling wave design allows for precise combination of the mixed and unmixed components of each sample. 
         [0050]    Relay to  FIG. 5 , traveling wave synthetic sampler  500  comprises the same features as traveling wave mixer  100 , except that it omits two of mixers  140 . The illustrated circuit produces only an even or odd sample, and additional circuitry is required to produce a corresponding odd or even sample.  FIGS. 6A through 6G  provide examples of such additional circuitry, as well as additional details that may be included in features shown in  FIG. 5 . 
         [0051]    Referring to  FIGS. 6A through 6G , traveling wave synthetic sampler  600  comprises an input transmission line  605 , an LO signal generation unit  610 , high band mixers  615 , low band amplifiers  620 , an odd sample combiner  625 , and an even sample combiner  630 . These features are generally arranged as shown in  FIG. 6A , and more detailed examples of the features in  FIG. 6A  are shown in  FIGS. 6B through 6G . In  FIGS. 6B through 6G , dotted lines indicate that the illustrated signal lines are connected to signal lines in a different figure, and the letters “A” through “S” indicate correspondences between those different signal lines. As illustrated in  FIGS. 6A through 6G , two output transmission lines and corresponding output filters are provided for the even and odd samples, rather than just one output transmission line. In addition, examples of differential signal lines and related components are shown in  FIGS. 6B through 6G , 
         [0052]    In the embodiments illustrated in  FIGS. 5 and 6 , both the low band and high band signals are sensed along a differential input line, then either mixed or amplified and combined onto two output differential pairs. These output pairs are then filtered to form the odd and even samples. As indicated above, the difference between even and odd samples is that is that the low band signal is subtracted from the high band signal to generate the odd sample, while the low band signal is added to the high band signal to generate the even sample. The odd and even samples produced in  FIG. 6  contain all the necessary information to reproduce the RE input signal. 
         [0053]    As indicated by the foregoing, in certain embodiments, a traveling wave mixer, sampler, or synthetic sampler can be implemented by incorporating transconductance amplifiers and mixers or samplers between a pair of transmission lines, and driving the mixers or samplers through an additional transmission line. Such devices provide various potential benefits relative to conventional technologies, such as improved bandwidth, gain, and noise characteristics, as well as reduced cost. 
         [0054]    While representative embodiments are disclosed herein, one of ordinary skill in the art appreciates that many variations that are in accordance with the present teachings are possible and remain within the scope of the appended claim set. The invention therefore is not to be restricted except within the scope of the appended claims.