JPH0640605B2 - Mixer circuit - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention is an improvement of a mixer circuit using a mixer to which a received signal wave and a local oscillation wave (local oscillation) are added and the frequency difference between them is output as an intermediate frequency signal. It is about.

[Background of the Invention]

Generally, in a mixer, if the input level of the received signal is high, in addition to the desired intermediate frequency signal between the received signal frequency and the local oscillation frequency, unnecessary high-frequency (distorted wave) components and images as sidebands Since signals and the like are output, suppression of these unnecessary waves becomes a problem.

In particular, in recent years, as miniaturized ICs such as tuners and converters using mixers have been developed, development of low-distortion mixers and image suppression mixers has become an important issue.

Representative conventional examples of the mixer circuit are described in JP-A-60-3234 and JP-A-56-75709.

To reduce the distortion of the mixer, there is a method of using a balance mixer as described in Japanese Patent Application Laid-Open No. 60-3234. However, this balance mixer has only the ability to suppress even-order distortion components, and it has an odd number. The next distortion component cannot be suppressed. Further, Japanese Patent Application Laid-Open No. 56-75709 describes an image cancellation type mixer, but the 90-degree phase shifter used in this mixer circuit uses a transmission line and therefore has a wide band. Not only the characteristics could not be obtained, but it was not suitable for IC production.

As described above, at present, sufficient characteristics have not been obtained in the low-distortion mixer and the image suppression mixer. Therefore, a tuner and a converter RF input circuit require a multi-stage filter for distortion suppression and image suppression, resulting in miniaturization, IC
There was a drawback that it hindered the conversion.

[Object of the Invention]

An object of the present invention is to provide a mixer circuit capable of completely suppressing distortion components and image signals with a simple configuration.

[Outline of Invention]

In order to achieve the above object, the present invention applies the configuration of a feedforward amplifier, which incorporates a feedforward method known as a distortion reduction method for an amplifier, to a mixer circuit.
That is, it is intended to obtain an intermediate frequency signal in which the distortion component is completely suppressed by extracting only the distortion component from the signal whose frequency has been converted by the mixer circuit and adding the distortion component in reverse phase to the original signal. Further, an image signal suppressing mixer circuit can be constructed by using two of these feedforward mixers, and a tuner suitable for miniaturization and IC can be obtained.

Example of Invention

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings.

FIG. 1 shows an embodiment of the present invention. This separates the high frequency signal input from the terminal 1 into two signals, one of which is input to the mixer 3 and the other of which is input to the mixer 4 through the attenuator (resistor) 2. The mixers 3 and 4 have a local oscillation circuit 5
A local oscillation signal is injected from the.

Since a high level high frequency signal is input to the mixer 3, various distortion components exist on the output side in addition to the intermediate frequency signal. On the other hand, since the high frequency signal input to the mixer 4 is a signal of a sufficiently low level that is attenuated by the attenuator (resistor) 2, only the intermediate frequency signal exists on the output side of the mixer 4, There is no distortion component of.

Here, a part of the signal on the output side of the mixer 3 is taken out, and the intermediate frequency signal containing this distortion component is attenuated by the attenuator 6 to the same level as the level of the intermediate frequency signal on the output side of the mixer 4 to obtain the difference. The phase addition is performed by the dynamic amplifier 7, and only the distortion component generated in the mixer 3 is output to the output side of the differential amplifier 7.

This distortion component is amplified by the differential amplifier 7 to the same level as the distortion component on the output side of the mixer 3, and the signal on the output side of the mixer 3 and the differential amplifier 8 are subjected to anti-phase addition and the distortion is output from the output terminal 9. Obtain an intermediate frequency signal with the components completely suppressed.

Here, the transmission gain of the attenuator 2 is A ₁ , the conversion gain of the mixer 3 is A ₂ , the conversion gain of the mixer 4 is A ₃ , the transmission gain of the attenuator 6 is A ₄ , and the amplification degree of the differential amplifier 7 is A _5. Assuming that the amplification degree of the differential amplifier 8 is A ₆ , it is necessary to satisfy the following two equations: A ₁ + A ₃ = A ₂ + A ₄ (b) A ₄ + A ₅ = 0 (b).

Further, since the input level to the differential amplifier 7 is sufficiently low, distortion does not occur. Further, since the distortion component is not generated in the differential amplifier 8, the differential amplifier 8 is used as a mere anti-phase adder having an amplification degree of 1, and A ₆ = 0.

FIG. 2 is a circuit diagram showing another embodiment of the present invention. In the embodiment shown in the figure, as the 180-degree phase shifter for anti-phase addition, the transmission lines 10 and 12 having a half wavelength of the intermediate frequency are used instead of the differential amplifier. Reference numeral 11 is an amplifier. Even with this circuit, the intermediate frequency signal in which the distortion component is completely suppressed can be obtained from the terminal 9.

FIG. 3 shows an image canceling mixer circuit using the distortion suppressing mixer shown in FIG. 1 as an application example of the present invention.

In FIG. 3, 12 is a first voltage controlled oscillator (hereinafter,
1 is abbreviated as VCO), 13 is a second voltage controlled oscillator (hereinafter abbreviated as second VCO), 14 is a phase detector, 1
5 is a loop amplifier, 16 is a loop filter, 17 is an adder, 19 is a first distortion suppression mixer (mixer circuit), 19 '
Is a second distortion suppression mixer, 11 is a 3 dB 90 ° power combiner,
Reference numeral 1 is an input terminal, 9 is an output terminal, 10 and 10 'are low-pass filters (LPF), 25 is a terminating resistor, 20 is a 3 dB power distributor, and 18 is a tuning voltage terminal.

Here, the image signal canceling operation will be described. The oscillation signal of the first VCO 12 whose oscillation signal frequency is controlled by the tuning voltage applied to the tuning voltage terminal 18 is transferred to the second VCO 13,
Phase detector 14, loop amplifier 15, loop filter 1
It is input to the phase detector 14 of the phase locked loop formed in 6.

As is well known, in the phase-locked loop, the phase of the input signal of the phase detector 14 and the phase of the oscillation signal of the voltage controlled oscillator (second VCO 13) in the phase-locked loop are almost the same in the steady state of synchronization. The phase difference of 90 ° is maintained,
Two signals having the same frequency and a phase difference of 90 ° are present at points a and b in the figure.

In this embodiment, the tuning voltage from the tuning voltage terminal 18 is directly applied to the first VCO 12, and to the second VCO 13 the output DC voltage of the phase detector 14 is superimposed by the adder 17 at the same time. For applying the first VCO 12 and the second VCO
Since the oscillation frequency difference of 13 is small and it is possible to maintain the synchronization state with respect to the wideband input signal without widening the frequency width for pulling in the phase synchronization in the second VCO 13, it is possible to shift the wideband 90 ° as a whole. A phaser is realized.

The output signal of this 90 ° phase shifter has a phase difference of 90 °,
It is input to the first distortion suppression mixer 19 and the second distortion suppression mixer 19 'through points a and b. An input signal is applied from the input terminal 1, equally divided by the 3 dB power divider 20, and input to the first distortion suppression mixer 19 and the second distortion suppression mixer 19 '.
Since the case where the intermediate frequency signal frequency becomes lower than the input signal frequency is explained here,
The signals mixed by the first distortion suppression mixer 19 and the second distortion suppression mixer 19 'are passed through the low-pass filters 10 and 10' to be c.
Appears at point d.

Hereinafter, this phase relationship will be described. The input signal e _i applied from the input terminal 1 is defined as e _i = E _s sin ω _s · t (1). Further, the local oscillation signal e _l1 input to the first distortion suppression mixer 19 through the point b is set to e _l1 = E _lcos ω _l · t (2), and passes through the point a to the second mixer 19 ′. The local oscillation signal e _l2 to be input is e _l2 = E _lsin ω _l · t (3), which is 90 ° out of phase with e _l1 . Further, the image signal e _IM is made in phase with the input signal, and e _IM = E _IMsin ω _IM · t (4). The frequency relationship of the image signal is ω _IM = 2ω _l −ω _s (5).

In the following, focusing on the phase relationship, only the phase components of the above equations (1) to (4) are used. Further, as described above, since the intermediate frequency signal frequency is set lower than the input signal frequency, the sum component is excluded from the mixed frequency components.

In the first distortion suppression mixer 19, the above (1) is applied to the input signal.
Mixing equations (2) and (2) and the above equations (4) and (2) for the image signal, removing the frequency component of the sum and focusing on the frequency component of the difference, the frequency conversion shown in the following equation is performed. .

_{sinω s · t × cosω l ·} tsin (ω l -ω s) t ......
_{(6) sinω IM · t ×} cosω l · tsin (ω l -ω IM) t = -sin (ω l -ω s) t ...... becomes (7). In the second distortion suppression mixer 19 ', the above equations (1) and (3) are applied to the input signal, and the above equation is applied to the image signal.
(4) and (3) were _{mixed, sinω s · t × sinω l} · tcos (ω l -ω s) t ...... (8) sinω IM · t × sinω l · tcos (ω l -ω IM ) T = cos (ω _l −ω _s ) t (9).

FIG. 4 shows the phase relationship between the intermediate frequency signal and the image signal appearing at points c and d in the figure, that is, the phase relationship of the above equations (6) to (9).

In FIG. 4, 21 is the phase of the intermediate frequency signal I _f1 at point c, 22 is the phase of the image signal I _m1 at point c, and 23 is d.
The phase of the intermediate frequency signal I _{f2 at} the point and 24 is the phase of the image signal I _m2 at the point d.

Each signal having a phase relationship as shown in FIG. 4 passes through points c and d and is input to the 3 dB 90 ° power combiner 11.

FIG. 5 shows the 3 dB 90 ° power combiner 11 together with the phase relationship of FIG. In FIG. 5, the intermediate frequency signal is indicated by a solid arrow and the image signal is indicated by a broken line. The 3 dB 90 ° power combiner 11 has points c to f between c and e, between e and f, between f and d, and d.
90 ° phase shift between −c and 180 ° phase shift between cf and de.

The signal input from point c is 90 ° phase shifted to point e, 180 ° phase shifted to f point output, and the signal input from point d is 90 ° phase shifted to f point 180 ° phase shifted. Output to point e respectively. Therefore, as shown in FIG. 5, at the point e, the intermediate frequency signals (21 'and 23') cancel each other and only the image signals (22 'and 24') are output, and at the point f, the image signal (22 'and 24 ') cancel each other and only the intermediate frequency signals (21' and 23 ') are output. Therefore, the image signal can be canceled by terminating the point e with the terminating resistor 25 and extracting the intermediate frequency signal from the point f.

Although the image signal and the input signal have the same phase in the above description, the similar image canceling operation is performed also when the phase of the image signal and the phase of the input signal have an arbitrary phase difference.

As described above, in the present embodiment, the local oscillation circuit has the configuration in which the first VCO 12 is added to the phase-locked loop and is linked with the second VCO 13 in the phase-locked loop by the tuning voltage. It is possible to supply two signals that are phase-shifted by 90 °, and it is possible to perform the above-mentioned image signal canceling operation even for a wide band input signal.

Further, since the mixers (mixer circuits) 19 and 19 'for distortion suppression shown in FIG. 1 are used in the mixer circuit, an intermediate frequency signal in which distortion components are completely suppressed must be obtained from the output terminal 9. You can

FIG. 6 shows an example in which the mixer circuit for suppressing the distortion component and suppressing the image signal shown in FIG. 3 is applied to a tuner circuit.

This is the RF input circuit with the RF amplifier 26 and the attenuator 2.
9. A feedforward amplifier for suppressing distortion, which includes differential amplifiers 27 and 28, is inserted.

This tuner uses a mixer circuit for distortion suppression and image signal suppression in the mixer circuit, and further uses a feedforward amplifier in the RF amplifier. Therefore, in the case of a conventional tuner or converter in the high-frequency signal input section. As described above, it is not necessary to configure the tuning filters in multiple stages, and therefore, there is an advantage that the tuner becomes a very small size.

Further, as described above, since there is generally no filter composed of LC, the circuit is suitable for IC integration.
The part surrounded by the broken line in the figure can be an IC of one chip, and the tuner can be made extremely small.

〔The invention's effect〕

According to the present invention, by extracting only the distortion component from the intermediate frequency signal containing the distortion component and constructing a feedforward type mixer circuit for performing anti-phase addition with the intermediate frequency signal containing the distortion component, the distortion component Will be completely suppressed.

Further, by using the mixer circuit capable of suppressing distortion according to the present invention, an image suppressing mixer including a 90-degree phase shifter using a PLL oscillation circuit and a hybrid circuit is configured, thereby a distortion suppressing filter and an image suppressing filter. Is unnecessary, and there is also a secondary advantage that a tube that can be miniaturized and integrated into an IC can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, and FIG. 3 is a circuit diagram showing an image canceling mixer circuit as an application example of the present invention. FIG. 4 is a vector diagram showing the phase relationship between the intermediate frequency signal and the image signal at points c and d of the circuit of FIG. 3, and FIG. 5 is the phase relationship of each signal in the main part of FIG. FIG. 6 is a circuit diagram showing a tuner circuit as still another application example of the present invention. Explanation of symbols 1 ... Input terminal, 2, 6 ... Attenuator, 3, 4 ... Mixer, 5 ... Local oscillation circuit, 7, 8 ... Differential amplifier, 9 ...
... Output terminals, 10, 12 ... 1/2 wavelength transmission line, 11
……amplifier

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Masaki Noda Inventor Masaki Noda 292 Yoshida-cho, Totsuka-ku, Yokohama City, Kanagawa Prefecture Home Appliances Research Laboratory, Hitachi, Ltd. Home Appliance Research Laboratory, Hitachi, Ltd.

Claims (1)

[Claims] 1. A first mixer to which a high-frequency signal is directly input, a second mixer to which the high-frequency signal is input via a first attenuator, and an output of the first mixer to a second mixer. A first anti-phase addition / amplification means for inputting to one input side through an attenuating means, directly inputting the output of the second mixer to the other input side, and adding and amplifying both When,
The output of the first mixer is directly input to one input side, and the output of the first anti-phase addition / amplification means is directly input to the other input side, both are subjected to anti-phase addition, amplification and output. An unwanted distorted wave that may appear on the output side of the first mixer in the intermediate frequency signal obtained as the output of the second anti-phase adding / amplifying means. A mixer circuit characterized in that a signal is suppressed on the way and does not appear.