JP2007013560A - Frequency converter and radio machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a consumption current and noises when inputting a small signal and the distortion of an output voltage from a mixer when inputting a large signal in an AB-class operation type mixer circuit incorporated into a frequency converter. <P>SOLUTION: The frequency converter has the AB-class operation type mixer circuit frequency-converting an input signal, a reference voltage source outputting a reference voltage and an output resistor being connected to the output end of the mixer circuit and converting an output current from the mixer circuit into the output voltage from the mixer. The frequency converter further has an in-phase voltage detecting comparison means for detecting an in-phase voltage at the output end of the mixer circuit, and comparing the in-phase voltage and the reference voltage. The frequency converter further has an active load device changing a load to a current flowing from between the output end of the mixer circuit and the output resistor according to the result of the comparison of the in-phase voltage detecting comparison means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a frequency converter technique, and more particularly to a frequency converter used for radio communication, an orthogonal modulation / demodulator using the same, and a radio using the same.

  In recent years, wireless terminals have been actively developed, and wireless terminals are becoming smaller and cheaper. The characteristics of a frequency converter that demodulates a signal received by an antenna into a baseband signal in a wireless terminal is low in current consumption when a small signal is input (when the signal power input to the frequency converter is zero or small). It is required to have low noise and to maintain linearity of input and output when a large signal is input (when the signal power input to the frequency converter is large).

  Incorporating a class AB operation mixer circuit consisting of an input transistor, a switching transistor, and an output resistor into a frequency converter is one of the methods that can satisfy such a requirement to some extent. DC current flowing through the input transistor and even-order distortion such as even-order distortion increase as the input signal increases. DC-mode current flowing through the input transistor and even-order distortion of the mixer output current are common-mode current flowing through the switching transistor and output resistor simultaneously. Current, which varies the voltage across the two output resistors. This causes fluctuations in the operating points of the input transistor and the two switching transistors, which in turn increases the distortion of the mixer output voltage (ie, the output voltage of the frequency converter).

  In order to suppress a large signal input fluctuation of the input transistor and the switching transistor, a configuration has been devised in which the output resistor is replaced with an active load device using a transistor (see, for example, Non-Patent Document 1). In this configuration, the common-mode voltage applied to the switching transistor and the reference voltage are compared by the comparison amplifier and feedback is applied to the active load, thereby suppressing the fluctuation of the voltage applied to the active load even if the common-mode current varies.

However, in this method, since the transistor as the active loader generates noise larger than that of the resistor, there is a problem that noise increases even though distortion of the mixer output voltage can be suppressed.
K. Kivekas, A.M. Parssinen, J.A. Jussila, J .; Ryoanen, K. et al. Halonen “DESIGN OF LOW-VOLTAGE ACTIVE MIXER FOR DIRECT CONVERSION RECEIVERS” Circuits and Systems, 2001. ISCAS 2001. The 2001 IEEE International Symposium on, Volume: 4, 6-9 May 2001 Pages: 382-385 vol. 4

  In view of the above problems, the present invention provides a class AB operation system mixer circuit incorporated in a frequency converter that suppresses current consumption and noise when a small signal is input, and suppresses distortion of the mixer output voltage when a large signal is input. Objective.

  The present invention is a class AB operation type mixer circuit that converts the frequency of an input signal, a reference voltage source that outputs a reference voltage, and an output terminal of the mixer circuit that converts the output current of the mixer circuit to a mixer output voltage. An output resistor that detects the common-mode voltage at the output terminal of the mixer circuit and compares the common-mode voltage with the reference voltage; and the output terminal of the mixer circuit and the output resistor. And an active loader in which a load with respect to a current flowing in between varies depending on a comparison result of the common-mode voltage detection / comparison means.

  The present invention also provides a class AB operation system mixer circuit for frequency conversion of an input signal, an output resistor connected to the output terminal of the mixer circuit for converting the output current of the mixer circuit to a mixer output voltage, and the mixer A transimpedance amplifier in which current flows from between the output terminal of the circuit and the output resistor; a first resistor having one end connected to one of two output terminals of the transimpedance amplifier; and the transimpedance amplifier A second resistor connected to the other end of the two output ends and the other end of the first resistor, a reference voltage source for outputting a reference voltage, the first resistor, and the second resistor A common-mode detection / comparison amplifier that outputs a differential amplification signal between the common-mode voltage obtained from the connection portion of the resistor and the reference voltage, and an inflow from the output terminal of the transimpedance amplifier Load on current that provides a frequency converter, characterized in that it comprises, an active load transistor that varies with the differential amplified signal.

  The present invention also provides an antenna, an amplifier that amplifies the signal received by the antenna, a class AB operation system mixer circuit that converts the frequency of the signal amplified by the amplifier, and a reference voltage source that outputs a reference voltage. An output resistor connected to the output terminal of the mixer circuit for converting the output current of the mixer circuit into a mixer output voltage; and detecting a common-mode voltage at the output terminal of the mixer circuit; and the common-mode voltage and the reference voltage Common-mode voltage detection and comparison means, and an active load device in which a load with respect to a current flowing from between the output terminal of the mixer circuit and the output resistor changes according to a comparison result of the common-mode voltage detection and comparison means, A channel select filter that selects a frequency conversion signal obtained as the mixer output voltage, and an amplitude adjustment of the output of the channel select filter To provide a radio receiver, characterized in that it comprises a variable gain amplifier, a.

  The present invention also includes an antenna, an amplifier that amplifies the signal received by the antenna, a class AB operation system mixer circuit that converts the frequency of the signal amplified by the amplifier, and the output terminal of the mixer circuit. An output resistor that converts the output current of the mixer circuit into a mixer output voltage, a transimpedance amplifier that receives current from between the output terminal of the mixer circuit and the output resistor, and 2 of the transimpedance amplifier. A first resistor having one end connected to one of the two output ends; a second resistor connected to the other end of the two output ends of the transimpedance amplifier and the other end of the first resistor; A reference voltage source for outputting a reference voltage, and a differential amplification signal of the reference voltage and an in-phase voltage obtained from a connection portion between the first resistor and the second resistor are output. The common-mode detection comparison amplifier, the load for the current flowing in from the output terminal of the transimpedance amplifier, the active load transistor that changes according to the differential amplification signal, and the frequency conversion signal obtained as the mixer output voltage are channel-selected. Provided is a radio device comprising a channel select filter and a variable gain amplifier that adjusts the amplitude of the output of the channel select filter.

  ADVANTAGE OF THE INVENTION According to this invention, the consumption current and noise at the time of a small signal input of a class AB operation system mixer circuit incorporated in a frequency converter can be suppressed, and distortion of the mixer output voltage at the time of a large signal input can be suppressed.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 is a configuration diagram of a direct conversion radio receiver according to the present embodiment.

  The radio receiver 100 includes an antenna 102, an amplifier 104, a frequency converter 200, a first channel select filter 106, a second channel select filter 107, a first variable gain amplifier 108, a second variable gain amplifier 109, and a synthesizer 110.

  A signal received by the antenna 102 is amplified by the low noise amplifier 104. The frequency converters 200 and 300 demodulate the RF signal, which is the output of the low noise amplifier 104, into a baseband signal (BB signal) by separating it into quadrature components using the L0 signal output from the synthesizer 110.

  The output signal of the frequency converter 200 is channel-selected by the channel select filter 106 and the amplitude is adjusted by the variable gain amplifier 108. The output signal of the other frequency converter 300 is channel-selected by the channel select filter 107 and the amplitude is adjusted by the variable gain amplifier 109.

  The frequency converter 200 will be described with reference to the circuit diagram of FIG.

  The frequency converter 200 includes a mixer circuit 201, active loaders 202 and 212, an in-phase detection comparator 203, a reference voltage source 204, output resistors 205 and 215, RF bias resistors 207 and 208, an RF input capacitor 209, and an RF bias power supply 210. Is provided.

  The mixer circuit 201 of this embodiment is a single-balance class AB operation mixer circuit including an input transistor 221 and switching transistors 222 and 223. The emitters of the switching transistors 222 and 223 are connected to the collector of the input transistor 221 whose emitter is grounded.

  One end of an RF input capacitor 209 is connected to the base of the input transistor 221. An RF signal is input from the other end of the RF input capacitor 209. One end of each of the RF bias resistors 207 and 208 is connected between the base of the input transistor 221 and one end of the RF input capacitor 209. An RF bias power source 210 is connected to the other end of the RF bias resistor 207, and a DC bias voltage is applied to the other end of the RF bias resistor 207. The other end of the RF bias resistor 209 is grounded. With this structure, an RF signal biased by a DC bias voltage is input to the base of the input transistor 221.

  The LO signal is differentially input to the bases of the switching transistors 222 and 223. The collectors of the switching transistors 222 and 223 serve as the output terminal of the mixer circuit 201.

  An active load device 202 and an output resistor 205 are connected in parallel to the collector of the switching transistor 222 which is the output terminal of the mixer circuit 201. The collector current of the switching transistor 222 is shunted to the active loader 202 and the output resistor 205. An active load device 212 and an output resistor 215 are connected in parallel to the collector of the switching transistor 223 which is the other output terminal. The collector current of the switching transistor 223 is shunted to the active load transistor 402 and the output resistor 405. Furthermore, the other ends of the output resistor 205 and the output resistor 215 are connected to each other. The common-mode detection comparator 203 detects the common-mode component of the voltage (that is, the mixer output voltage) between the collector of the switching transistor 222 and the collector of the switching transistor 223. The common-mode detection comparator 203 compares the detected common-mode voltage with the reference voltage output from the reference voltage source 204. Based on this comparison result, the load of the active loader 202 is controlled, and the amount of current shunted from the collector of the switching transistor 222 to the active loader 202 is changed. Further, the load of the active loader 212 is controlled based on the comparison result, and the amount of current that is shunted from the collector of the switching transistor 223 to the active loader 212 is changed. As a result, the in-phase component of the current flowing through the output resistors 205 and 215 is kept constant, and the in-phase component of the mixer output voltage is kept almost constant.

  The mixer output voltage is output to the channel select filter 106 as a BB signal.

  Note that the output resistors 205 and 215 may have equivalent resistance values. The switching transistors 222 and 223 may have the same characteristics. The active loads 202 and 212 may have the same characteristics as each other. By doing so, it is possible to obtain a frequency converter 200 in which the mixer output voltage has characteristics that are positive and negative.

  Here, the operation of the frequency converter 200 will be described according to the case of the magnitude of the RF signal.

  An operation when the power of the RF signal is 0 will be described. An in-phase detection comparator 203 detects an in-phase component of the mixer output voltage. The common-mode detection comparator 203 compares the detected common-mode voltage with the reference voltage output from the reference voltage source 204, controls the active load devices 202 and 212 based on the comparison result, and flows to the output resistors 205 and 215. Control to keep the in-phase component of the current constant. As a result, the in-phase component of the mixer output voltage is kept substantially constant.

  An operation when the power of the RF signal is small will be described. When the RF signal input to the base of the input transistor 221 of the mixer circuit 201 through the RF input capacitor 209 is small, the direct current between the emitter and collector of the input transistor 221 increases due to the base-emitter voltage characteristics of the input transistor 221. Since there is almost no increase in current between the emitters and collectors of the switching transistors 222 and 223, the operation is almost the same as when the amplitude of the RF signal is zero. Therefore, the in-phase component of the mixer output voltage is kept almost constant.

  As described above, when the amplitude of the RF signal is 0 or small as in the standby state of the radio receiver 100, the emitter-collector current of the input transistor 221 hardly changes, and consequently the emitters of the switching transistors 222 and 223. The current between the collectors also hardly changes. The power consumption of the frequency converter 200 is determined only by the current determined by the DC bias voltage applied to the base of the input transistor 221, and further current consumption can be avoided.

  Further, since the current flowing through the active loads 202 and 212 is smaller than the current flowing through the output resistors 205 and 215, the noise generated by the active loads 202 and 212 is compared with the noise generated by the output resistors 205 and 215. The effect on the mixer output voltage is small.

  The operation when the RF signal is relatively large will be described. If the RF signal input to the base of the input transistor 221 via the RF input capacitor 209 is sufficiently large, a direct current increases between the emitter and the collector of the input transistor 221 due to the base-emitter voltage characteristics of the input transistor 221, The direct current between the emitter and collector of the switching transistors 222 and 223 also increases. Therefore, the common-mode component of the mixer output voltage also increases, and the mixer output voltage tends to decrease as the operating points of the switching transistors 222 and 223 change. However, the common-mode detection comparator 203 detects an increase in the common-mode component of the mixer output voltage, compares the detected common-mode voltage with the reference voltage output from the reference voltage source 204, and determines the active loaders 202 and 212 based on the comparison result. Since control is performed so that the in-phase component of the current flowing through the output resistors 205 and 215 is kept constant, the in-phase component of the mixer output voltage is kept almost constant. Therefore, the common-mode current flowing in the output resistors 205 and 215 is kept constant at substantially the same value as when the RF signal is relatively small. As a result, the operating points of the input transistor 221 and the switching transistors 222 and 223 are stabilized, so that the linearity of the mixer output voltage with respect to the RF signal is ensured.

  The current flowing through the active loaders 202 and 212 increases, and the noise generated by the active loaders 202 and 212 also increases. However, since the signal obtained as the mixer output voltage is also large, the effect of the noise of the active loaders 202 and 212 on it. Is small.

  As described above, during operation of the wireless receiver 100, whether the RF signal is relatively small or large, the linearity of the mixer output voltage with respect to the RF signal is ensured while the mixer output voltage is The influence of noise of the active loaders 202 and 212 can be suppressed to a low level.

  Therefore, according to the present embodiment, the current consumption and noise at the time of small signal input and the distortion of the mixer output voltage at the time of large signal input of the class AB operation system mixer circuit incorporated in the frequency converter are suppressed. be able to.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described.

  The radio receiver 100 according to the present embodiment includes a frequency converter 400 shown in the circuit diagram of FIG. 3 instead of the frequency converters 200 and 300 of the radio receiver 100 according to the first embodiment. The frequency converter 400 is replaced with the active load transistors 402 and 412, the common-mode detection comparison amplifier 403, and the common-mode detection resistor instead of the active loads 202 and 212 and the common-mode detection comparator 203 of the frequency converter 200 of the first embodiment. Devices 413 and 423 are provided.

  The frequency converter 400 shown in FIG. 3 includes a mixer circuit 401, active load transistors 402 and 412, an in-phase detection comparison amplifier 403, an in-phase detection resistor 413 and 423, a reference voltage source 404, output resistors 405 and 415, and an RF bias resistor 407. 408, an RF input capacitor 409, and an RF bias power source 410.

  The mixer circuit 401 is a single balance AB class operation mixer circuit including an input transistor 421 and switching transistors 422 and 423. The emitters of the switching transistors 422 and 423 are connected to the collector of the input transistor 421 whose emitter is grounded.

  One end of an RF input capacitor 409 is connected to the base of the input transistor 421. An RF signal is input from the other end of the RF input capacitor 409. One end of each of the RF bias resistors 407 and 408 is connected between the base of the input transistor 421 and one end of the RF input capacitor 409. An RF bias power source 410 is connected to the other end of the RF bias resistor 407, and a DC bias voltage is applied to the other end of the RF bias resistor 407. The other end of the RF bias resistor 409 is grounded. With this structure, an RF signal biased by a DC bias voltage is input to the base of the input transistor 421.

  The LO signal is differentially input to the bases of the switching transistors 422 and 423. The collectors of the switching transistors 422 and 423 become the output terminal of the mixer circuit 401.

  The source of the active load transistor 402 and one end of the output resistor 405 are connected to the collector of the switching transistor 422 that is the output end of the mixer circuit 401. The drain of the active load transistor 402 and the other end of the output resistor 405 are also connected to each other, and the active load transistor 402 and the output resistor 405 are connected in parallel. One end of the common-mode detection resistor 413 is connected to the collector of the switching transistor 422. The collector current of the switching transistor 422 is shunted to the active load transistor 402 and the output resistor 405.

  The source of the active load transistor 412 and one end of the output resistor 415 are connected to the collector of the switching transistor 423 which is the other output terminal. The drain of the active load transistor 412 and the other end of the output resistor 415 are also connected to each other, and the active load transistor 412 and the output resistor 415 are connected in parallel. One end of the common-mode detection resistor 423 is connected to the collector of the switching transistor 423. The collector current of the switching transistor 423 is shunted to the active load transistor 412 and the output resistor 415. Further, the other ends of the output resistor 405 and the output resistor 415 are connected to each other.

  The other ends of the common-mode detection resistor 413 and the common-mode detection resistor 423 are connected to each other. If the resistance values of the common-mode detection resistor 413 and the common-mode detection resistor 423 are equal, the voltage at the connection between the two is almost equal to the average value of the voltage between the output terminals of the mixer circuit 401, that is, the common-mode component of the mixer output voltage. Will be equal.

  The common-mode detection comparison amplifier 403 differentially amplifies the voltage at the connection between the common-mode detection resistor 413 and the common-mode detection resistor 423 and the reference voltage output from the reference voltage source 404, and outputs a differential amplification signal.

  The active load transistors 402 and 412 are MOS transistors in this embodiment. The outputs of the common-mode detection comparison amplifier 403 are input to the gates of the active load transistors 402 and 412. As the output of the common-mode detection / comparison amplifier 403 increases, the current that flows from the collector of the switching transistor 222 to the active load transistor 402 increases. Further, the current that is shunted from the collector of the switching transistor 223 to the active load transistor 412 is increased by the output of the common-mode detection comparison amplifier 403. As a result, the in-phase component of the current flowing through the output resistors 405 and 415 is kept constant, and the in-phase component of the mixer output voltage is kept almost constant.

  The mixer output voltage is output to the channel select filter 106 as a BB signal.

  The output resistors 405 and 415 may have the same resistance value. The switching transistors 422 and 423 may have the same characteristics. The active load transistors 402 and 412 may have the same characteristics as each other. By doing so, it is possible to obtain a frequency converter 400 in which the mixer output voltage has characteristics that are positive and negative.

  Here, the operation of the frequency converter 400 will be described with respect to the magnitude of the RF signal.

  An operation when the power of the RF signal is 0 will be described. An in-phase detection comparison amplifier 403 differentially amplifies the in-phase component of the mixer output voltage and the reference voltage of the reference voltage source 404. Since the common-mode detection comparison amplifier 403 is connected to the gates of the active load transistors 402 and 412, if the common-mode component of the mixer output voltage exceeds the reference voltage of the reference voltage source 404, the drain-source between the active load transistors 402 and 412 The current increases to prevent an increase in current flowing through the output resistors 405 and 415. As a result, the in-phase component of the mixer output voltage is kept substantially constant.

  An operation when the power of the RF signal is small will be described. When the RF signal input to the base of the input transistor 421 of the mixer circuit 401 via the RF input capacitor 409 is small, the direct current between the emitter and the collector of the input transistor 421 increases due to the base-emitter voltage characteristics of the input transistor 421. Since there is almost no increase in the current between the emitters and collectors of the switching transistors 422 and 423, the operation is almost the same as when the amplitude of the RF signal is zero. Therefore, the in-phase component of the mixer output voltage is kept almost constant.

  As described above, when the amplitude of the RF signal is 0 or small as in the standby state of the radio receiver 100, the emitter-collector current of the input transistor 421 hardly changes, and consequently the emitters of the switching transistors 422 and 423. The current between the collectors also hardly changes. The power consumption of the frequency converter 400 is determined only by the current determined by the DC bias voltage applied to the base of the input transistor 221, and further current consumption can be avoided.

  Further, since the current flowing through the active load transistors 402 and 412 is smaller than the current flowing through the output resistors 405 and 415, the noise generated by the active load transistors 402 and 412 is compared with the noise generated by the output resistors 405 and 415. The effect on the mixer output voltage is small.

  The operation when the RF signal is relatively large will be described. If the RF signal input to the base of the input transistor 421 via the RF input capacitor 409 is sufficiently large, a direct current increases between the emitter and the collector of the input transistor 421 due to the base-emitter voltage characteristics of the input transistor 421, The direct current between the emitter and collector of the switching transistors 422 and 423 also increases. Therefore, the common-mode component of the mixer output voltage also increases, and the mixer output voltage tends to decrease as the operating points of the switching transistors 222 and 223 change. However, the common-mode detection comparison amplifier 403 differentially amplifies the common-mode component of the mixer output voltage and the reference voltage of the reference voltage source 404, and the active load transistor according to the difference between the common-mode component of the mixer output voltage and the reference voltage of the reference voltage source 404. The current between the drain and source of 402 and 412 is increased to prevent an increase in current flowing through the output resistors 205 and 215. As a result, the common-mode current flowing through the output resistors 405 and 415 is kept constant at substantially the same value as when the RF signal is relatively small. Therefore, the operating points of the input transistor 421 and the switching transistors 422 and 423 are stabilized, so that the linearity of the mixer output voltage with respect to the RF signal is ensured.

  The current flowing through the active load transistors 402 and 412 increases and the noise generated by the active load transistors 402 and 412 also increases. However, since the signal obtained as the mixer output voltage is also large, the influence of the noise of the active load transistors 402 and 412 on it. Is small.

  As described above, during operation of the wireless receiver 100, whether the RF signal is relatively small or large, the linearity of the mixer output voltage with respect to the RF signal is ensured while the mixer output voltage is The influence of noise on the active load transistors 402 and 412 can be reduced.

  Therefore, according to the present embodiment, the current consumption and noise at the time of small signal input and the distortion of the mixer output voltage at the time of large signal input of the class AB operation system mixer circuit incorporated in the frequency converter are suppressed. be able to.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described.

  The radio receiver 100 of this embodiment includes a frequency converter 600 shown in the circuit diagram of FIG. 4 in place of the frequency converters 200 and 300 of the radio receiver 100 of the first embodiment. The frequency converter 600 is obtained by connecting a transimpedance amplifier 650 to the output terminal of the mixer circuit 601.

  A frequency converter 600 shown in FIG. 4 includes a mixer circuit 601, active load transistors 602 and 612, RF bias resistors 607 and 608, an RF input capacitor 609, an RF bias power supply 610, a common-mode detection comparison amplifier 603, and common-mode detection resistors 613 and 623. , A reference voltage source 604, output resistors 605 and 615, and a transimpedance amplifier 650.

  The mixer circuit 601 of this embodiment is a class AB operation system mixer circuit including an input transistor 621 and switching transistors 622 and 623. The emitters of the switching transistors 622 and 623 are connected to the collector of the input transistor 621 whose emitter is grounded.

  One end of an RF input capacitor 609 is connected to the base of the input transistor 621. An RF signal is input from the other end of the RF input capacitor 609. One end of each of the RF bias resistors 607 and 608 is connected between the base of the input transistor 621 and one end of the RF input capacitor 609. An RF bias power source 610 is connected to the other end of the RF bias resistor 607, and a DC bias voltage is applied to the other end of the RF bias resistor 607. The other end of the RF bias resistor 609 is grounded. With this structure, an RF signal biased by a DC bias voltage is input to the base of the input transistor 621.

  The LO signal is differentially input to the bases of the switching transistors 622 and 623. The collectors of the switching transistors 622 and 623 become the output terminal of the mixer circuit 601.

  One end of the output resistor 605 and one end of the input end of the transimpedance amplifier 650 are connected to the collector of the switching transistor 622 which is the output end of the mixer circuit 601. One end of the output resistor 615 and the other end of the input end of the transimpedance amplifier 650 are connected to the collector of the switching transistor 623 which is the other output end of the mixer circuit 601. The other ends of the output resistor 605 and the output resistor 615 are connected to each other.

  The transimpedance amplifier 650 includes a constant current source 651, transistors 652 and 662, and feedback resistors 653 and 663. The base of the transistor 652 is connected to one end of the output resistor 605 as one end of the input end of the transimpedance amplifier 650. The feedback resistor 653 is connected to the collector and base of the transistor 652. The collector of the transistor 652 becomes one end of the output terminal of the transimpedance amplifier 650.

  The base of the transistor 662 is connected to one end of the output resistor 615 as the other end of the input end of the transimpedance amplifier 650. The feedback resistor 663 is connected to the collector and base of the transistor 662. The collector of the transistor 662 is the other end of the output terminal of the transimpedance amplifier 650.

  The emitters of the transistors 652 and 662 are connected to each other, and a constant current source 651 is connected thereto.

  The source of the active load transistor 602 and one end of the common-mode detection resistor 613 are connected to the collector of the transistor 652 that is one end of the output terminal of the transimpedance amplifier 650. The collector current of the transistor 652 as the output terminal of the transimpedance amplifier is shunted to the active load transistor 602 and the feedback resistor 653. The source of the active load transistor 612 and the other end of the common-mode detection resistor 623 are connected to the collector of the transistor 662, which is the other end of the output terminal of the transimpedance amplifier 650. The collector current of the transistor 662 as the output terminal of the transimpedance amplifier is shunted to the active load transistor 612 and the feedback resistor 663. The other ends of the common-mode detection resistor 613 and the common-mode detection resistor 623 are connected to each other. If the resistance values of the common-mode detection resistor 613 and the common-mode detection resistor 623 are equal, the voltage at the connection portion between them is the average value of the voltage between the output terminals of the transimpedance amplifier 650, that is, the common mode of the transimpedance amplifier output voltage. It becomes almost equal to the component.

  The common-mode detection comparison amplifier 603 differentially amplifies the voltage at the connection between the common-mode detection resistor 613 and the common-mode detection resistor 623 and the reference voltage output from the reference voltage source 606, and outputs a differential amplification signal.

  The active load transistors 602 and 612 are MOS transistors in this embodiment. The drains of the active load transistors 602 and 612 are connected to each other. The outputs of the common-mode detection / comparison amplifier 603 are input to the gates of the active load transistors 602 and 612. As the output of the common-mode detection / comparison amplifier 603 increases, the current that is shunted from the collector of the transistor 652 to the active load transistor 602 increases. Further, the current that is shunted from the collector of the transistor 662 to the active load transistor 612 is increased by the output of the common-mode detection comparison amplifier 603. As a result, the in-phase component of the current flowing through the feedback resistors 653 and 663 is kept constant, and the in-phase component of the transimpedance amplifier output voltage is kept almost constant. The transimpedance amplifier output voltage is output to the channel select filter 106 as a BB signal.

  The output resistors 605 and 615 may have equivalent resistance values. The switching transistors 622 and 623 may have the same characteristics as each other. The active load transistors 602 and 612 may have equivalent characteristics. The feedback resistors 653 and 663 may have equivalent resistance values. The transistors 652 and 662 may have the same characteristics as each other. By doing so, it is possible to obtain a frequency converter 600 in which the mixer output voltage has characteristics that are positive and negative.

  Here, the operation of the frequency converter 600 will be described according to the case of the magnitude of the RF signal.

  An operation when the power of the RF signal is 0 will be described. The in-phase component of the current flowing through the output resistors 605 and 615 appears as the in-phase component of the transimpedance amplifier output voltage. The common-mode detection comparison amplifier 603 differentially amplifies the common-mode component of the transimpedance amplifier output voltage and the reference voltage of the reference voltage source 604. Since the common-mode detection comparison amplifier 603 is connected to the gates of the active load transistors 602 and 612, when the common-mode component of the transimpedance amplifier output voltage exceeds the reference voltage of the reference voltage source 604, the drain-source of the active load transistors 602 and 612 The current between increases. Then, the change of the in-phase component of the transimpedance output voltage tends to be suppressed, and an increase in the current flowing through the output resistors 605 and 615 is also prevented.

The in-phase component of the transimpedance amplifier output voltage is kept almost constant.

  The operation when the RF signal is small will be described. When the RF signal inputted to the base of the input transistor 621 of the mixer circuit 601 through the RF input capacitor 609 is small, the direct current between the emitter and the collector of the input transistor 621 increases due to the base-emitter voltage characteristics of the input transistor 621. Since there is almost no increase in the current between the emitters and collectors of the switching transistors 622 and 623, the operation is almost the same as when the amplitude of the RF signal is zero. Therefore, the in-phase component of the transimpedance amplifier output voltage is kept almost constant.

  As described above, when the amplitude of the RF signal is 0 or small as in the standby state of the radio receiver 100, the emitter-collector current of the input transistor 621 hardly changes, and consequently the emitters of the switching transistors 622 and 623 The current between the collectors also hardly changes. The power consumption of the frequency converter 600 is determined only by the current determined by the DC bias voltage applied to the base of the input transistor 621, and further current consumption can be avoided.

  In addition, since the current flowing through the output terminal of the transimpedance amplifier 650 is small, the current flowing through the active load transistors 602 and 612 is small, and the influence on the mixer output voltage is small.

  The operation when the RF signal is relatively large will be described.

  If the RF signal input to the base of the input transistor 621 via the RF input capacitor 609 is sufficiently large, a direct current increases between the emitter and the collector of the input transistor 621 due to the base-emitter voltage characteristics of the input transistor 621, The direct current between the emitter and collector of the switching transistors 622 and 623 also increases. If the in-phase component of the current flowing through the output resistors 605 and 615 thereby increases, the voltage at the collectors of the switching transistors 622 and 623 changes and the operating point changes, so that the mixer output voltage drops.

  However, since the current of the collector of the switching transistor 622 is shunted not only to the output resistors 605 and 615 but also to the transimpedance amplifier 650, the emitters of the switching transistors 622 and 623 are better than the structure where the transimpedance amplifier 650 is not connected. -The increase in the DC current between the collectors has little influence on the change in the operating point of the switching transistors 622 and 623, and the change in linearity of the transimpedance amplifier output voltage with respect to the RF signal can be reduced.

  Further, the common-mode detection / comparison amplifier 603 differentially amplifies the in-phase component of the transimpedance amplifier output voltage and the reference voltage of the reference voltage source 604, and the difference between the in-phase component of the transimpedance amplifier output voltage and the reference voltage of the reference voltage source 604 is obtained. Accordingly, the current between the drain and source of the active load transistors 602 and 612 is increased. As a result, changes in the in-phase component of the transimpedance output voltage are suppressed.

  If the RF signal is relatively large, the current flowing through the active load transistors 602 and 612 also increases and the noise generated by the active load transistors 602 and 612 increases. However, since the signal obtained as the transimpedance amplifier output voltage is large, the active load transistor The effects of noise at 602 and 612 are small.

  As described above, when the radio receiver 100 is operated, the transimpedance amplifier output voltage is ensured to be linear with respect to the RF signal, regardless of whether the RF signal is relatively small or large. The influence of noise of the active load transistors 602 and 612 on the amplifier output voltage can be reduced.

  Therefore, according to the present embodiment in which the transimpedance amplifier and the active load transistor are combined, the current consumption and noise at the time of small signal input of the class AB operation system mixer circuit incorporated in the frequency converter are suppressed, and the large signal input The distortion of the mixer output voltage at the time can be suppressed.

  In the above embodiment, the mixer circuits 200, 400, and 600 have been described as single-balance mixer circuits. However, other types of mixer circuits such as a double-balance mixer may be used.

The lineblock diagram of the radio receiver of a 1st embodiment. The circuit diagram of the frequency converter of a 1st embodiment. The circuit diagram of the frequency converter of 2nd Embodiment. The circuit diagram of the frequency converter of 3rd Embodiment.

Explanation of symbols

100: wireless receiver 102 ... antenna 104 ... amplifier,
200, 300, 400, 600 ... frequency converter 106 ... first channel select filter 107 ... second channel select filter 108 ... first variable gain amplifier 109 ... second variable gain amplifier 110 ... synthesizers,
207, 208, 407, 408, 607, 608 ... RF bias resistors 209, 409, 609 ... RF input capacitors 210, 410, 610 ... RF bias power supplies 221, 421, 621 ... Input transistor 222 , 223, 422, 423, 622, 623 ... switching transistors 402, 412, 602, 612 ... active load transistors 403, 603 ... common-mode detection comparison amplifiers 413, 423, 613, 623 ... common-mode detection Resistor 650, transimpedance amplifier 651, constant current source 652, 662, transistor 653, 663, feedback resistor

Claims (6)

A class AB operation mixer circuit that converts the frequency of the input signal;
A reference voltage source for outputting a reference voltage;
An output resistor connected to an output terminal of the mixer circuit and converting an output current of the mixer circuit into a mixer output voltage;
A common-mode voltage detection / comparison means for detecting a common-mode voltage at the output terminal of the mixer circuit and comparing the common-mode voltage with the reference voltage;
An active load device in which a load with respect to a current flowing from between the output terminal of the mixer circuit and the output resistor changes according to a comparison result of the common-mode voltage detection comparison unit;
A frequency converter comprising: A first resistor having one end connected to one end of two output ends of the mixer circuit;
A second resistor connected to the other end of the two output ends of the mixer circuit and the other end of the first resistor;
The common-mode voltage detection / comparison means is a common-mode detection / comparison amplifier that outputs a differential amplification signal of a common-mode voltage obtained from a connection portion between the first resistor and the second resistor and the reference voltage.
The active load device is an active load transistor in which a load with respect to a current flowing from between the output terminal of the mixer circuit and the output resistor is changed by the differential amplification signal. The frequency converter described. A class AB operation mixer circuit that converts the frequency of the input signal;
An output resistor connected to the output terminal of the mixer circuit and converting an output current of the mixer circuit into a mixer output voltage;
A transimpedance amplifier into which a current flows from between the output terminal of the mixer circuit and the output resistor;
A first resistor having one end connected to one of the two output ends of the transimpedance amplifier;
A second resistor connected to the other end of the two output ends of the transimpedance amplifier and the other end of the first resistor;
A reference voltage source for outputting a reference voltage;
A common-mode detection / comparison amplifier that outputs a differential amplification signal between a common-mode voltage obtained from a connection between the first resistor and the second resistor and the reference voltage;
An active load transistor in which a load with respect to a current flowing from the output terminal of the transimpedance amplifier is changed by the differential amplification signal;
A frequency converter comprising: An antenna,
An amplifier for amplifying a signal received by the antenna;
A class AB operation mixer circuit that converts the frequency of the signal amplified by the amplifier;
A reference voltage source for outputting a reference voltage;
An output resistor connected to the output terminal of the mixer circuit for converting the output current of the mixer circuit into a mixer output voltage; and detecting the common-mode voltage at the output terminal of the mixer circuit; and the common-mode voltage and the reference voltage A common-mode voltage detection and comparison means for comparison;
An active load device in which a load with respect to a current flowing from between the output terminal of the mixer circuit and the output resistor changes according to a comparison result of the common-mode voltage detection comparison unit;
A channel select filter for channel-selecting a frequency conversion signal obtained as the mixer output voltage;
A variable gain amplifier for adjusting the amplitude of the output of the channel select filter;
A wireless device comprising: A first resistor having one end connected to one end of two output ends of the mixer circuit;
A second resistor connected to the other end of the two output ends of the mixer circuit and the other end of the first resistor;
The common-mode voltage detection / comparison means is a common-mode detection / comparison amplifier that outputs a differential amplification signal of a common-mode voltage obtained from a connection portion between the first resistor and the second resistor and the reference voltage.
5. The active load device is an active load transistor in which a load with respect to a current flowing from between the output terminal of the mixer circuit and the output resistor is changed by the differential amplification signal. The radio described. An antenna,
An amplifier for amplifying a signal received by the antenna;
A class AB operation mixer circuit that converts the frequency of the signal amplified by the amplifier;
An output resistor connected to the output terminal of the mixer circuit and converting an output current of the mixer circuit into a mixer output voltage;
A transimpedance amplifier into which a current flows from between the output terminal of the mixer circuit and the output resistor;
A first resistor having one end connected to one of the two output ends of the transimpedance amplifier;
A second resistor connected to the other end of the two output ends of the transimpedance amplifier and the other end of the first resistor;
A reference voltage source for outputting a reference voltage;
A common-mode detection / comparison amplifier that outputs a differential amplification signal between a common-mode voltage obtained from a connection between the first resistor and the second resistor and the reference voltage;
An active load transistor in which a load with respect to a current flowing from the output terminal of the transimpedance amplifier is changed by the differential amplification signal;
A channel select filter for channel-selecting a frequency conversion signal obtained as the mixer output voltage;
A variable gain amplifier for adjusting the amplitude of the output of the channel select filter;
A wireless device comprising:

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