JP2008200188A - Radio transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a micromini radio transmitter having resistance to fluctuation in a supply voltage, consuming low amounts of power and being suited to a capsule type endoscope. <P>SOLUTION: This radio transmitter includes: a comparator 4 operating within a prescribed supply voltage range, shaping input signals 41 into rectangular wave-like balance signals and outputting them; a low pass filter 5 for attenuating components more than third and higher harmonics contained in the output signals 43 from the comparator and outputting sinusoidal balance signals; a mixer circuit 7 consisting of a circuit using a CMOS switch mechanism non-passing a direct current, mixing the sinusoidal balance signals with oscillating frequency signals and outputting the balance signals of radio frequency; a power amplifier 8 for converting the balance signals of radio frequency from the mixer circuit 7 into unbalance signals and amplifying them; and a band pass filter 9 for removing signals in unnecessary frequency band from the output signals of the power amplifier 8. The respective sections are formed in a CMOS process containing no organic substance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless transmitter used as a wireless transmission unit of a capsule endoscope.

It is expected that the capsule endoscope is easier to drink than the tube endoscope, and the burden on the patient is reduced (see Patent Document 1). For practical use, imaging information in the body is transmitted wirelessly to a receiver outside the body, so it is essential to realize an ultra-small transmitter that sends a large amount of data in real time. For such transmitters, wireless LAN (IEEE802.11a, 802.11g) or UWB (Ultra Wide Band) system applications can be considered, but these were developed for packet data communication such as personal computers. There are problems such as difficulty in sending a real-time image, high power consumption, and a large circuit size, which makes it difficult to reduce the size. Since the wireless transmitter of the capsule endoscope transmits a large amount of data, a wide frequency band is required, and the antenna built in the capsule needs to be downsized. A microwave band of 1.2 GHz or 2.4 GHz has been studied as a transmitter frequency band for solving this problem.
JP-A-2005-73885

  As a power supply method in the capsule endoscope, there are a method of supplying power from the inside by incorporating a battery inside the capsule and a method of supplying power from outside the living body using electromagnetic induction. In the method of supplying power from the inside, since the power consumption of the wireless unit is large, there is a problem that video information cannot be sent for a long time, and the number of pixels that can be sent per second is small, and the part that you want to see cannot be seen. is there. On the other hand, in the method of supplying power from the outside, the power supply voltage changes depending on the position of the capsule in the living body, and it is difficult to always derive a uniform image as a high frequency signal due to the influence of the voltage fluctuation. .

  Also, in a conventional capsule endoscope, an LC chip component or SAW (Surface Acoustic Wave) is provided at the output of the transmitter in order to reduce unnecessary spurs outside the frequency band to be used and impedance matching with the transmission antenna. ), The size of these parts is large, and the radio device cannot be miniaturized. In addition, compound semiconductors are preferably used for radio components, especially active devices that operate up to microwaves, but these compound semiconductors often contain harmful substances such as arsenic and are used in vivo. As a capsule endoscope, the user's health may be impaired.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a wireless transmitter suitable for a capsule endoscope that is ultra-compact, resistant to fluctuations in power supply voltage, and has low power consumption. is there.

  A wireless transmitter according to the present invention is a wireless transmitter that is used as a wireless transmission unit of a capsule endoscope and receives a signal indicating biological information converted into phase information as an input signal, and has a predetermined power supply voltage. A comparator that operates within the range, shapes the input signal into a square-wave balance signal, and outputs it, and outputs a sinusoidal balance signal by attenuating the third and higher harmonic components contained in the output signal from the comparator And a mixer circuit that mixes a sine wave signal and an oscillation frequency signal and outputs a radio frequency balance signal. .

  The wireless transmitter according to the present invention is preferably made by a complementary metal oxide semiconductor (CMOS) process that does not contain harmful substances. Thereby, even when applied to a capsule endoscope, a wireless transmitter that is safe for health can be provided.

  In the wireless transmitter according to the present invention, the phase-converted input signal is once shaped by the comparator into a rectangular wave-shaped balance signal within a predetermined power supply voltage range, so that a performance strong against fluctuations in the power supply voltage can be obtained. In addition, since the mixer circuit is composed of a circuit using a CMOS switch function that does not pass a direct current, performance that is strong against fluctuations in the power supply voltage can be obtained, and power consumption can be reduced. Further, it can cope with a signal in the microwave band, which is advantageous for downsizing.

  In the wireless transmitter according to the present invention, a power amplifier that converts and amplifies a radio frequency balanced signal from the mixer circuit into an unbalanced signal, and a bandpass filter that removes an unnecessary frequency band signal from the output signal of the power amplifier You may make it provide further.

In the wireless transmitter according to the present invention, the comparator includes, for example, a two-stage amplifier circuit that amplifies an input signal, a current regulating circuit that regulates a current flowing through the two-stage amplifier circuit, and a two-stage amplifier. A synthesis circuit that synthesizes and amplifies each output from the circuit, a feedback circuit that feeds back the output signal from the synthesis circuit to a two-stage amplifier circuit, and a waveform of the output signal from the synthesis circuit into a square-wave balance signal It is preferable to have a shaping circuit for shaping and outputting.
The comparator may further include an attenuation circuit that optimizes the amplitude by attenuating the amplitude of the input signal and applies a predetermined DC voltage, and a reference voltage generation circuit that generates a reference voltage of the comparator.

  In the wireless transmitter according to the present invention, the mixer circuit includes, for example, a pair of input terminals to which a balanced signal is input, first and second MOS transistors in which source terminals are interconnected, and one end of the mixer circuit is first. And a first capacitor connected to the source terminal of the second MOS transistor and having the other end connected to one of the pair of input terminals, and a third and fourth MOS transistor having the source terminals connected to each other, A second capacitor having one end connected to the source terminals of the third and fourth MOS transistors and the other end connected to the other of the pair of input terminals; and the gate terminals of the first to fourth MOS transistors. A bias voltage is applied to the other pair of input terminals for inputting the oscillation frequency signal and the source and drain terminals of the first to fourth MOS transistors. And a bias voltage applying terminal for applying, it is preferable that a configuration of a passive mixer.

  According to the wireless transmitter of the present invention, the phase-converted input signal is once shaped by a comparator into a rectangular wave-shaped balance signal within a predetermined power supply voltage range and output. Strong performance can be obtained. In addition, since the mixer circuit is configured by a circuit using a CMOS switch function that does not allow direct current to flow, it is possible to obtain performance that is resistant to fluctuations in the power supply voltage and to reduce power consumption. In addition, it is possible to deal with microwave band signals, which is advantageous for downsizing.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a configuration example in which a wireless transmitter according to an embodiment of the present invention is applied to a wireless transmission unit of a capsule endoscope. The capsule endoscope includes a wireless transmission unit 1, a CCD (Charge Coupled Device) 2, a baseband circuit 3, and a transmission antenna 11.

  The CCD 2 captures the inside of a living body and outputs an image signal indicating biological information. The baseband circuit 3 converts the image signal from the CCD 2 into a digital baseband signal 41. The baseband circuit 3 performs processing for converting an image signal into phase information as conversion processing. The radio transmission unit 1 generates a radio frequency transmission signal using the baseband signal 41 as an input signal. The transmission antenna 11 radiates the transmission signal generated by the wireless transmission unit 1 as an electromagnetic wave.

  The wireless transmission unit 1 includes a comparator 4, a low pass filter (LPF) 5, a gain control circuit (GC) 6, a mixer 7, a power amplifier (PA) 8, a band pass filter (BPF) 9, an oscillator ( OSC) 10. The wireless transmission unit 1 is formed using a CMOS device having sufficient performance in the microwave band, for example, formed by a CMOS process of 0.13 μm or 90 nm. Note that the CMOS device has improved high-frequency performance by microfabrication and does not contain toxic compounds.

  2 to 6 show specific configuration examples of the respective units of the wireless transmission unit 1. 7 to 9 show signal waveforms of the respective units of the wireless transmission unit 1.

FIG. 2 shows a specific configuration example of the comparator 4.
The comparator 4 operates within a predetermined power supply voltage range (between 0 V and the power supply voltage (Vdd)), and shapes the input signal 41 into a rectangular wave-shaped balance signal 43 (see FIG. 7) and outputs it. As shown in FIG. 2, the comparator 4 has a plurality of resistance elements and a plurality of MOS transistors. The comparator 4 has a two-stage amplifier circuit (a first amplifier 56 and a second amplifier 57) that amplifies the input signal 41. The comparator 4 also attenuates the amplitude of the input signal 41 to optimize the amplitude and provide a predetermined DC voltage, and a reference voltage generation circuit that generates the reference voltage Vc (see FIG. 7) of the comparator 4. 52. The comparator 4 also includes a current regulation circuit 53 that regulates the current flowing through the amplifier circuit having the two-stage configuration, an operational amplifier (synthesis circuit) 54 that synthesizes and amplifies the outputs from the amplifier circuit having the two-stage configuration, A feedback circuit that feeds back an output signal from 54 to an amplifier circuit having a two-stage configuration, and a shaping circuit 55 that shapes the output signal from the synthesis circuit 54 into a rectangular wave-shaped balance signal 43 and outputs the waveform. The feedback circuit has a resistor R6. The comparator 4 has an input terminal 13 for inputting a signal 41 and a pair of output terminals 14 and 15 for outputting a balance signal (signal 43).

FIG. 3 shows a specific configuration example of the low-pass filter 5.
The low-pass filter 5 attenuates a component higher than the third harmonic contained in the output signal 43 from the comparator 4 and outputs a sine wave-like balance signal 44 (see FIG. 7). As shown in FIG. 3, the low-pass filter 5 includes a plurality of resistance elements and a plurality of capacitors. The low-pass filter 5 has a first filter circuit 61 whose trap frequency is set in the vicinity of three times the baseband frequency, and a second filter circuit 62 that attenuates a frequency five times or more. The low-pass filter 5 has a pair of input terminals 37 and 38 for inputting a balance signal (signal 43) and a pair of output terminals 39 and 40 for outputting a balance signal (signal 44).

FIG. 4 shows a specific configuration example of the gain control circuit 6.
The gain control circuit 6 adjusts the output signal 44 from the low-pass filter 5 to an optimum level for the dynamic operation of the circuit after the next stage. As shown in FIG. 4, a plurality of resistance elements and a plurality of MOS transistors are provided. And a switch. The gain control circuit 6 has a pair of input terminals 18 and 19 for inputting a balance signal (signal 44) and a pair of output terminals 20 and 21 for outputting a balance signal (signal 45). The gain control circuit 6 also has setting input terminals 22 and 23.24 to which a gain setting signal from an external circuit (not shown) is input.

FIG. 5 shows a specific configuration example of the mixer 7.
The mixer 7 is composed of a circuit using a CMOS switch function that does not pass a direct current, and mixes a sine wave signal 45 and an oscillation frequency signal to output a radio frequency balance signal 48. As shown in FIG. 5, the mixer 7 has a passive mixer configuration having a plurality of resistance elements, a plurality of capacitors, and a plurality of MOS transistor switches. The mixer 7 includes a pair of input terminals 25 and 26 to which a balance signal 45 is input, first and second MOS transistors Q23 and Q24 whose source terminals are interconnected, and first and second MOS transistors at one end. The first capacitor C1 is connected to the source terminals of the transistors Q23 and Q24 and the other end is connected to one of the pair of input terminals 25 and 26 (input terminal 25). The mixer 7 also has third and fourth MOS transistors Q25 and Q26 whose source terminals are connected to each other, one end connected to the source terminals of the third and fourth MOS transistors Q25 and Q26, and the other end. And a second capacitor C2 connected to the other of the pair of input terminals 25 and 26 (input terminal 26). The mixer 7 also includes another pair of input terminals 29 and 30 for inputting an oscillation frequency signal to the gate terminals of the first to fourth MOS transistors Q23, Q24, Q25, and Q26, and the first to fourth MOS transistors Q23. , Q24, Q25, Q26 are connected to a bias voltage applying terminal 31 for applying a bias voltage to the source terminal and drain terminal, and to the drain terminals of the first to fourth MOS transistors Q23, Q24, Q25, Q26. Output terminals 27 and 28 for outputting a balance signal 48 are provided.

  The power amplifier 8 converts the radio frequency balance signal 48 from the mixer 7 into an unbalanced signal and amplifies it. The band pass filter 9 removes a signal in an unnecessary frequency band from the output signal of the power amplifier 8. The band pass filter 9 can be configured as a tuned band pass type using a drain load inductor formed on a chip. FIG. 6 shows a specific configuration example for realizing the functions of the power amplifier 8 and the band pass filter 9. The circuit shown in FIG. 6 includes a balanced input / unbalanced output amplifier 35. The circuit shown in FIG. 6 also includes a current source 37, a resistor R15, MOS transistors Q27 and Q28, capacitors C5 and C6, an inductor L1 at the drain of the MOS transistor Q27, and a parasitic capacitance C7 at the drain of the MOS transistor Q27. Yes. A tuned band-pass filter is formed by the inductor L1 and the parasitic capacitance C7.

  Next, the operation of the capsule endoscope, particularly the details of the function and operation of each circuit portion of the wireless transmission unit 1 will be described.

  The wireless transmission unit 1 converts the baseband signal 41 output from the baseband circuit 3 into a microwave signal of, for example, 1.2 GHz or 2.4 GHz and sends the converted signal to the transmission antenna 11. The digital baseband signal 41 is usually a rectangular wave signal, but if the power saving of the baseband circuit 3 is achieved, the high frequency characteristics deteriorate and the complete rectangular wave is not obtained (see FIG. 7). In the wireless transmission unit 1, such a baseband signal 41 is waveform-shaped by the comparator 4.

  The comparator 4 operates between 0 V and the power supply voltage (Vdd), and the amplitude of the output signal 43 of the comparator 4 is a rectangular wave of 0 to Vdd (see FIG. 7). Even if Vdd changes due to exhaustion of the internal battery in the method of supplying power from the inside of the capsule or the state of electromagnetic coupling from an external power source in the method of supplying power from the outside, even if Vdd changes. From the characteristic of the comparator 4, only the amplitude of the signal changes, and the phase characteristic and the frequency characteristic do not change. As a specific value, the signal amplitude of the comparator output when the power supply voltage changes to ½ is 6 dB lower, and the other characteristics hardly change. This capsule endoscope uses a method in which image information is converted into the phase of an RF signal, and as described above, the phase of the output signal 43 of the comparator 4 does not change even if the power supply voltage changes. There is no information degradation. Further, the output amplitude of the comparator 4 is related to the transmission power, and the above-mentioned reduction of 6 dB is only a state where the transmission power from the transmission antenna 11 is reduced by 6 dB. Don't be.

  In the circuit of the comparator 4 in FIG. 2, an input signal 41 is input to the input terminal 13 and applied to the MOS transistors Q2 and Q9 via the resistors R1, R2 and R3 (signal 42). The resistors R1, R2, and R3 (attenuation circuit 51) have a function of attenuating the input signal 41 to an optimum amplitude and a function of applying a DC voltage. The signal 42 applied to the MOS transistors Q2 and Q9 is attenuated to the optimum amplitude as shown in FIG.

  2, resistors R4 and R5 (reference voltage generation circuit 52) provide a reference voltage Vc (see FIG. 7) to be compared by the comparator 4. MOS transistors Q1, Q2, Q3, Q4 and Q6, Q7, Q8, Q9 form a first amplifier 56 and a second amplifier 57. Outputs from the first amplifier 56 and the second amplifier 57 are combined by a combining circuit 54 including MOS transistors Q12, Q13, Q14, and Q15, and positively fed back to the MOS transistors Q2 and Q9 by a feedback circuit using a resistor R6. To do. Current source 17 and MOS transistors Q11, Q5, Q10 (current regulating circuit 53) determine the currents of the amplifiers of MOS transistors Q1, Q2, Q3, Q4 and Q6, Q7, Q8, Q9. MOS transistors Q16, Q17 and Q18, Q19 (shaping circuit 55) further shape the comparator signal into a rectangular wave, and send balance signal 43 from the pair of output terminals 14, 15.

  In FIG. 8, a waveform 46 indicates the frequency characteristic of the low-pass filter 5. Waveforms 47 a to 47 d show the spectrum of the output signal of the comparator 4. In particular, the waveform 47a represents the fundamental component (primary component) of the output signal, the waveform 47b represents the third harmonic component, the waveform 47c represents the fifth harmonic component, and the waveform 47d represents the seventh harmonic component.

  As the low-pass filter 5, a filter having a cutoff frequency that attenuates a harmonic component that is three times or more the signal 43 that has passed through the comparator 4 is used. Since the rectangular wave signal is composed of odd-order components (primary, third-order, fifth-order, seventh-order,...), A signal obtained by attenuating the third-order component or more is a sine wave. Therefore, the output signal 44 of the low-pass filter 5 is a signal close to a sine wave (see FIG. 7). The low-pass filter 5 is composed of an RC filter or an RC active filter, and is hardly affected by fluctuations in the power supply voltage.

  In the circuit of the low-pass filter 5 of FIG. 3, resistors R16, R17, R18, R19 and a capacitor C7, and capacitors C10, C11, C12, C13 and a resistor R22 (first filter circuit 61) are Zen-T type notch filters. The trap frequency is set in the vicinity of three times the baseband frequency. Resistors R20 and R21 and capacitors C8 and C9 (second filter circuit 62) are low-pass filters that attenuate a frequency five times or more.

  In the gain control circuit 6 of FIG. 4, the output signal 44 from the low-pass filter 5 is input to input terminals 18 and 19. The MOS transistors Q20, Q21, and Q22 operate as switches that are turned on and off by a gain setting signal that is input to the setting input terminals 22, 23, and 24 from an external circuit (not shown). The signal 44 input to the gain control circuit 6 is set to an optimum size by the resistors R6 and R7 and the resistor R8 (or R9 and R10). Since the MOS transistors Q20, Q21, and Q22 are operated in a mode in which no direct current flows, the gain control circuit 6 has a characteristic that is not affected by the power supply voltage.

  The mixer 7 converts the signal 45 that has passed through the gain control circuit 6 into, for example, a 2.4 GHz or 1.2 GHz microwave signal based on the oscillation frequency signal of the oscillator 10. The circuit of the mixer 7 in FIG. 5 is a Gilbert type, and the drain terminals and the source terminals of the MOS transistors Q23, Q24, Q25, and Q26 are short-circuited in a DC manner by resistors R11 and R12. Further, a bias voltage of, for example, 1/5 × Vdd to 1/2 × Vdd is applied from the bias voltage application terminal 31 to the source terminals and drain terminals of the MOS transistors Q23, Q24, Q25, Q26 via resistors R13, R14. Applied. The oscillation frequency signal from the oscillator 10 is input to terminals 29 and 30, whereby a signal having an amplitude of approximately 0-Vdd is applied to the gate terminals of the MOS transistors Q23, Q24, Q25, and Q26 constituting the Gilbert cell. ing. The output signal of the oscillator 10 is output from an inverter type amplifier composed of NMOS and PMOS. Capacitors C1, C2, C3, and C4 are for DC decoupling.

  MOS transistors Q23, Q24, Q25, and Q26 are in an ON state (a state where the impedance between the drain and the source is low) when the gate voltage is high with respect to the source, and when the voltage is 0 V and a negative voltage with respect to the source. The characteristics of the OFF state (the state where the impedance between the drain and the source is high) are shown. The voltage applied via the resistors 13 and 14 is a bias voltage for making the OFF states of the MOS transistors Q23, Q24, Q25, and Q26 more complete. Therefore, when the signal state applied to the terminal 29 is a level of Vdd and the signal state applied to the terminal 30 is 0 V in the signal from the oscillator 10, the MOS transistor Q23 and the MOS transistor Q26 are in the ON state, and the MOS transistor Q24 The MOS transistor Q25 is turned off. When the signal from the oscillator 10 has a signal state applied to the terminal 29 at a level of 0V and the signal state applied to the terminal 30 has a level of Vdd, the MOS transistor Q23 and the MOS transistor Q26 are in the OFF state, Transistor Q24 and MOS transistor Q25 are turned on.

  In this manner, the baseband signals applied to the terminals 25 and 26 are converted from the terminals 27 and 28 into the radio frequency balance signal 48 having the spectrum shown in FIG. 9 by the double balance mixer operation. Is output. Such a mixer is called a passive mixer because no direct current flows. The passive mixer does not depend on the power supply voltage. Therefore, the signal passing through the mixer 7 is not affected by fluctuations in the power supply voltage.

  The radio frequency balance signal 48 from the mixer 7 is amplified by the power amplifier 8. Thereafter, an unnecessary signal outside the band is further suppressed by the bandpass filter 9 and transmitted to the transmission antenna 11 as a transmission signal. The circuit in FIG. 6 realizes the functions of the power amplifier 8 and the bandpass filter 9. In the circuit of FIG. 6, an input signal 48 is input to terminals 32 and 33, is input to a MOS transistor Q27 via a balanced input-unbalanced output amplifier 35, and is amplified by the MOS transistor Q27. A tuned bandpass filter is formed by the inductance L1 of the drain of the MOS transistor Q27 and the parasitic capacitance C7 of the drain to attenuate unnecessary components of the signal. The amplified signal is supplied to the transmission antenna 11 via the capacitor C5. Current source 37, MOS transistor 28, and resistor R15 provide a bias for MOS transistor Q27.

  As described above, according to the wireless transmitter according to the present embodiment, as the wireless transmission unit 1 of the capsule endoscope, the power transmission voltage is not affected, the power consumption is small, the size is small, and It becomes possible to realize a product that does not contain harmful substances.

In addition, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible.
For example, in the above embodiment, image information captured by the CCD 2 is input to the wireless transmission unit 1 as a signal indicating biological information, but some biological information other than the image information is input. May be.

It is a block diagram which shows one structural example which applied the radio | wireless transmitter which concerns on one embodiment of this invention to the radio | wireless transmission part of a capsule endoscope. FIG. 2 is a circuit diagram illustrating a specific configuration example of a comparator in FIG. 1. It is a circuit diagram which shows the specific structural example of the low-pass filter in FIG. FIG. 2 is a circuit diagram illustrating a specific configuration example of a gain control circuit in FIG. 1. It is a circuit diagram which shows the specific structural example of the mixer in FIG. FIG. 2 is a circuit diagram illustrating a specific configuration example of a power amplifier and a band pass filter in FIG. 1. It is a wave form diagram which shows the signal waveform of each part in FIG. It is a wave form diagram which shows the spectrum of the output part of the comparator in FIG. It is a wave form diagram which shows the spectrum of the output part of the mixer in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Wireless transmission part, 2 ... CCD, 3 ... Baseband circuit, 4 ... Comparator, 5 ... Low pass filter, 6 ... Gain control circuit, 7 ... Mixer, 8 ... Power amplifier, 9 ... Band pass filter, 10 ... Oscillator, 11: Transmitting antenna.

Claims (6)

A wireless transmitter that is used as a wireless transmission unit of a capsule endoscope and receives a signal indicating biological information converted into phase information as an input signal,
A comparator that operates within a predetermined power supply voltage range, shapes the input signal into a rectangular-wave-shaped balance signal, and outputs it;
A low-pass filter for attenuating a component higher than the third harmonic contained in the output signal from the comparator and outputting a sine-wave-like balance signal;
A wireless transmission comprising a circuit using a CMOS switch function that does not pass a direct current, and a mixer circuit that mixes the sine wave signal and the oscillation frequency signal and outputs a balance signal of a radio frequency Machine. A power amplifier that converts and amplifies the radio frequency balance signal from the mixer circuit into an unbalanced signal;
The wireless transmitter according to claim 1, further comprising: a band-pass filter that removes an unnecessary frequency band signal from the output signal of the power amplifier. The comparator is
A two-stage amplifier circuit for amplifying an input signal;
A current regulating circuit for regulating a current flowing through the amplifier circuit having the two-stage configuration;
A synthesis circuit for synthesizing and amplifying respective outputs from the two-stage amplifier circuit;
A feedback circuit that feeds back an output signal from the synthesis circuit to the two-stage amplifier circuit;
The wireless transmitter according to claim 1, further comprising: a shaping circuit that shapes the output signal from the synthesis circuit into a rectangular wave-shaped balance signal and outputs the waveform. The comparator further comprises:
An attenuation circuit that attenuates the amplitude of the input signal to optimize the amplitude and provides a predetermined DC voltage;
The wireless transmitter according to claim 3, further comprising: a reference voltage generation circuit that generates a reference voltage of the comparator. The mixer circuit is
A pair of input terminals to which a balance signal is input;
First and second MOS transistors whose source terminals are interconnected;
A first capacitor having one end connected to the source terminals of the first and second MOS transistors and the other end connected to one of the pair of input terminals;
A third MOS transistor and a fourth MOS transistor whose source terminals are interconnected;
A second capacitor having one end connected to the source terminals of the third and fourth MOS transistors and the other end connected to the other of the pair of input terminals;
A pair of other input terminals for inputting an oscillation frequency signal to the gate terminals of the first to fourth MOS transistors;
5. A passive mixer having a bias voltage application terminal for applying a bias voltage to a source terminal and a drain terminal of each of the first to fourth MOS transistors. The wireless transmitter according to any one of the above. The wireless transmitter according to any one of claims 1 to 5, wherein the wireless transmitter is formed by a CMOS process.

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