JPS61289710A - Frequency conversion circuit - Google Patents

Abstract

PURPOSE:To improve the conversion power gain and conversion noise figure by providing a varactor means interlocking with a tuning means between an input terminal and common of a mixing circuit and changing the attenuation of a high frequency signal and a local oscillation wave by two peaking circuits in interlocking with the tuning means. CONSTITUTION:The varactor diode means 25 inserted between the input terminal and common of the mixing circuit consists of a variable range correcting capacitor 23 and a varactor diode 24. Further, the two peaking circuits are formed by the varactor diode means 25 and a series resonance circuit comprising a high frequency signal pickup coil 3 and a local oscillation wave pickup coil 15. The attenuation of the high frequency signal of the resonated low frequency is small and the attenuation of the high frequency deviated from the resonance is increased in the 1st peaking circuit. The 2nd peaking circuit is operated conversely as above. Thus, the injection level of the local oscillation wave to the mixing circuit is made a flat frequency characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a frequency conversion circuit for mixing a high frequency signal and a local oscillation wave and extracting a frequency-converted signal.

(Conventional technology) An example of a conventional frequency conversion circuit is shown in FIG.

In FIG. 2, the emitter terminal, which is the input end of the frequency conversion transistor 1, is connected via a high frequency signal injection capacitor 2 to the other end of a high frequency signal pickup coil 3, one end of which is grounded. The high frequency signal pickup coil 3 is arranged so as to be electromagnetically coupled to the crotch secondary side resonance line 4, and is selected by the tuning means 5 including the crotch secondary side resonance line 4. The tuning means 5 for extracting a high frequency signal includes, as is well known, an interstage secondary resonance line 49, an interstage secondary resonance variable capacitance diode 6, an interstage secondary termination capacitor 7, a coil 89, an interstage primary Variable capacitance diode for side resonance 91 Inter-stage primary side termination capacitance 10. Crotch primary side resonance line 11. High frequency input terminal 1
2, etc., and a high-frequency signal of an appropriate frequency is tuned and selected by the tuning voltage applied to the tuning voltage application terminal 13. Further, the emitter terminal of the frequency conversion transistor 1 is connected via a local oscillation wave injection capacitor 14 to the other end of a local oscillation wave pickup coil 15 whose one end is grounded. This local oscillation wave pickup coil 15 is arranged so as to be electromagnetically coupled to the local oscillation wave resonance line 1B.
A local oscillation wave whose frequency is controlled in conjunction with the tuning means 5 is taken out from a local oscillation means 17 which includes a local oscillation wave resonant line 1B9 for local oscillation resonance, as is well known. Variable capacitance diode 1B9
Local oscillation Clapp capacitance 19. It is composed of a local oscillator 20 and the like, and outputs an appropriate local oscillation wave in conjunction with the tuning means 5 using a tuning voltage applied to a tuning voltage application terminal 13. The base terminal of the frequency conversion transistor 1 is grounded via a ground capacitor 21, and the collector terminal is connected to an intermediate frequency signal output terminal 22.

In this configuration, the high frequency signal selected by the tuning means 5 by the tuning voltage is extracted by the high frequency signal pickup coil 3 by electromagnetic inductive coupling and given to the emitter terminal of the frequency conversion transistor l, and the frequency is controlled by the tuning voltage. The local oscillation wave of the local oscillation means 17 is extracted by the local oscillation wave pickup coil 15 by electromagnetic induction coupling and is applied to the emitter terminal of the frequency conversion transistor 1. Then, the high frequency signal and the local oscillation wave are mixed by this frequency conversion transistor 1 which acts as a mixing circuit, and the frequency is converted and an intermediate frequency signal is output from the collector terminal of the frequency conversion transistor 1 to the intermediate frequency signal output terminal 22. Ru.

(Problems to be Solved by the Invention) By the way, in order to improve the conversion power gain and conversion noise figure of the frequency conversion circuit, it is necessary to It is desirable to have a flat frequency characteristic.However, since the selectivity Q of the tuning circuit on the crotch primary side and the interstage secondary side of the tuning means 5 changes with frequency, the injection level of the high frequency signal is Low frequencies drop. This is shown by a solid line in the frequency vs. high frequency signal injection voltage characteristic diagram of FIG.

In addition, the injection level of the local oscillator wave is determined by the fact that the output of the local oscillator 20 using a transistor decreases in the oscillation wave at a high frequency, and the impedance of the conductor or printed pattern that leads the oscillation wave of the local oscillator 20 to the mixing circuit. High frequency local oscillation waves are degraded due to loss and the like. This is shown by a solid line in the frequency versus local oscillation wave injection voltage characteristic diagram of FIG.

In this way, in conventional frequency conversion circuits, the injection level of the high-frequency signal and local oscillation wave changes depending on the frequency, so the injection level is not insufficient at low frequencies for high-frequency signals and at high frequencies for local oscillation waves. set to size. For this reason, at low frequencies there is an excess of local oscillator waves, and at high frequencies there is an excess of high frequency signals. Therefore, the conventional frequency conversion circuit has a problem of low conversion power gain and poor conversion noise figure.

Incidentally, in order to flatten the frequency characteristics of the injection level to the mixing circuit, a buffer amplifier or the like may be interposed between the tuning means 5 and the local oscillation means 17 and the mixing circuit, but the frequency conversion Problems arise in that the space required by the circuit is large and the manufacturing cost is high.

An object of the present invention is to solve the above problems of the conventional frequency conversion circuit, and by adding a simple circuit configuration, it is possible to increase the injection level of high frequency signals and local oscillation waves injected into the mixing circuit. The object of the present invention is to provide a frequency conversion circuit with flat frequency characteristics and excellent conversion power gain and conversion noise figure.

(Means for Solving the Problem) In order to achieve the above object, the frequency conversion circuit of the present invention connects a high frequency signal pickup coil for taking out the high frequency signal selected by the tuning means to the input end of the mixing circuit, and A frequency conversion circuit comprising a local oscillation wave pickup coil connected to an input end of the mixing circuit for extracting a local oscillation wave from a local oscillation means whose frequency is controlled in conjunction with a tuning means, between the input end of the mixing circuit and ground. and a variable capacitance means interlocked with the tuning means.

(Function) Since the variable capacitance means interlocked with the tuning means is provided between the input end of the mixing circuit and the ground, a first peaking circuit is formed by the series resonant circuit of the variable capacitance means and the high frequency signal pickup coil. Further, a second peaking circuit is formed by a series resonant circuit of the variable capacitance means and the local oscillation wave pickup coil. The amount of attenuation of the high frequency signal and local oscillation wave by these first and second peaking circuits changes in conjunction with the tuning means, and the injection level of the high frequency signal and local oscillation wave into the mixing circuit has a flat frequency characteristic. becomes.

(Description of Embodiments) Hereinafter, embodiments of the frequency conversion circuit of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram of an embodiment of a frequency conversion circuit according to the present invention. In FIG. 1, the same and equivalent circuits as those in FIG. 2 are given the same reference numerals and redundant explanations will be omitted.

The difference between the frequency conversion circuit shown in FIG. 1 and the one shown in FIG. 2 is that a variable range correction capacitor 23 and a variable capacitance diode 24 are connected in series between the emitter terminal of the frequency conversion transistor l and the ground. The tuning voltage applied to the tuning voltage application terminal 13 is applied to the variable capacitance diode 24.

Then, the variable range correction capacitor 23 and the variable capacitance diode 2
4 constitutes a variable capacitance means 25 interposed between the input end of the mixing circuit and ground. moreover.

The series resonant circuit of the variable capacitance means 25 and the high frequency signal pickup coil 3 forms a first peaking circuit, and the series resonant circuit of the variable capacitance means 25 and the local oscillation wave pickup coil 5 forms a second peaking circuit. is formed. Here, the variable capacitance means 25 is the tuning means 5
is the tuning voltage that selects the high frequency signal with the low frequency.
The peaking circuit resonates with the low frequency of the high frequency signal, and the second peaking circuit resonates with the high frequency of the local oscillation wave by the tuning voltage at which the local oscillation means 17 outputs a high frequency local oscillation wave. It is set as follows. Further, the variable range correction capacitor 23 is provided to adjust the range of change in the capacitance value of the variable capacitance means 25 to an appropriate width with respect to the range of change in the capacitance value of the variable capacitance diode 24 due to the tuning voltage. It is something that was given.

In such a configuration, the first peaking circuit has a small amount of attenuation of a high frequency signal with a low frequency that resonates, and a large amount of attenuation of a high frequency signal with a high frequency that deviates from resonance. Therefore, the injection level of the high frequency signal into the mixing circuit can be made to have flat frequency characteristics as shown by the broken line in FIG. In addition, the second peaking circuit has a small attenuation amount for the resonant high-frequency local oscillation wave, and a large attenuation amount for the low-frequency local oscillation wave that deviates from resonance. Therefore, the local oscillation wave to the mixing circuit is 4th injection level
Incidentally, as shown by the broken line, a flat frequency characteristic can be achieved. Although the high frequency signal and the local oscillation wave are attenuated by the addition of the variable capacitance means 25, it is only necessary to set the output at a level corresponding to the amount of attenuation in advance.

Therefore, in the frequency conversion circuit of the present invention, a high frequency signal and a local oscillation wave with flat frequency characteristics are given to the input end of the mixing circuit, and the injection level of one of them does not become excessive due to a change in frequency, and the converted power can be reduced. It has high gain and a good conversion noise figure.

In addition, in the above embodiment, a mixing circuit is shown in which the input terminal is the input terminal of the frequency conversion transistor 1, but it goes without saying that the mixing circuit is not limited to the above embodiment. As explained above, the frequency conversion circuit according to the present invention is provided with the variable capacitance means interlocked with the tuning means between the input end of the mixing circuit and the ground. A first peaking circuit is formed by a series resonant circuit of the -/p coil, and a second peaking circuit is formed by a series resonant circuit of the variable capacitance means and the local oscillation wave pickup coil. And these first and second
The amount of attenuation of the high frequency signal and the local oscillation wave by the peaking circuit is rapidly changed by the tuning means, and the injection level of the high frequency signal and the local oscillation wave into the mixing circuit has flat frequency characteristics. Therefore, the conversion power gain can be high and the conversion noise figure can be made good. Moreover, the frequency conversion circuit of the present invention merely has a variable capacitance means with a simple circuit structure interposed between the input end of the mixing circuit and the ground, and its structure is different from that of the conventional one in which a buffer amplifier is added. It is simple and has an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the frequency conversion circuit of the present invention, FIG. 2 is a circuit diagram of an example of a conventional frequency conversion circuit, and FIG. FIG. 4 is a frequency versus high frequency signal injection voltage characteristic diagram of the frequency conversion circuit shown in FIGS. 1 and 2, and FIG. 4 is a frequency versus local oscillation wave injection voltage characteristic diagram of the true wave number conversion circuit shown in FIGS. 1- Frequency conversion transistor. 3: High frequency signal pickup coil, 5: Tuning means, 13: Tuning voltage application terminal, 15: Local oscillation wave pickup coil, 17: Local oscillation means, 23: Variable range correction capacitor, 24: Variable capacitance diode, 25: Variable capacity means.

Claims (3)

[Claims] (1) A high-frequency signal pickup coil for taking out the high-frequency signal selected by the tuning means is connected to the input end of the mixing circuit, and a local oscillation wave is taken out from the local oscillation means whose frequency is controlled in conjunction with the tuning means. A frequency conversion circuit comprising a pickup coil connected to an input end of the mixing circuit, further comprising variable capacitance means interlocked with the tuning means between the input end of the mixing circuit and ground. (2) The frequency conversion circuit according to claim 1, wherein the variable capacitance means is constructed by connecting a variable range correction capacitor and a variable capacitance diode in series. (3) The tuning means is a tuning voltage signal that selects a high frequency signal with a low frequency, and the first peaking circuit formed by a series circuit of the variable capacitance means and the high frequency signal pickup coil selects a high frequency signal with a low frequency. A tuning voltage signal that resonates with the signal and causes the local oscillation means to output a local oscillation wave of a high frequency, and a second peaking circuit formed by a series circuit of the variable capacitance means and the local oscillation wave pickup coil. 3. The frequency conversion circuit according to claim 1, wherein the frequency conversion circuit is configured to resonate with a local oscillation wave of a high frequency.