JPH06350473A - High frequency circuit - Google Patents

Abstract

PURPOSE:To avoid or relax influence by a capacitance value on frequency band characteristic by containing a variable capacitance element in a grounded high frequency capacitor, and varying the capacitance value corresponding to an operating frequency. CONSTITUTION:A high frequency signal is inputted to the RF input terminal 11 on one side of a mixer circuit 1 and a grounded high frequency capacitor Cg to the terminal 12 on the other side of it. The grounded high frequency capacitor Cg is formed by a composite capacitance circuit consisting of a fixed capacitor C1 interposed in parallel with the input terminal 12, a fixed capacitor C2 interposed in series, and the variable capacitance element Cv interposed in parallel. The capacitance value of the grounded high frequency capacitor Cg can be always set to the optimum condition by varying the capacitance value of the variable capacitance element Cv by a control voltage Vc set variablly corresponding to the operating frequency when an operating frequency band is wide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology effective when applied to a high-frequency circuit, and further to a balanced high-frequency circuit formed by using active elements such as transistors. The present invention relates to a technique effectively applied to a balanced mixer or a differential type high frequency amplifier circuit which is made into a circuit device.

[0002]

2. Description of the Related Art Generally, many high frequency circuits such as mixers and amplifiers using transistors, especially high frequency circuits integrated into an IC, have a differential circuit form, and therefore a balanced type input terminal. Many have.

When an unbalanced high frequency signal is input to a high frequency circuit having this balanced input terminal, one of the pair of balanced input terminals 11 and 12 (11) as shown in FIG.
A high frequency signal is input to and the other side (12) is connected to the high frequency grounding capacitance Cg.

The high-frequency circuit shown in FIG. 6 is a high-frequency conversion circuit.
Balanced mixer circuit with 1-stage cascade connection, 1
Reference numerals 1 and 12 are RF (high frequency) input terminals, Cg is high frequency ground capacitance, and 13 and 14 are Lo (local signal) input terminals, 2
Is an IF (intermediate frequency) output circuit, and 21 is an IF output terminal.

Regarding the balanced mixer circuit,
For example, the outline is described in "Design of High Frequency Circuits", published by CQ Publisher, Daijiro Kubo, pp. 187-189 (balanced modulation circuit by IC).

[0006]

However, the present inventors have clarified that the above-mentioned technique has the following problems.

That is, in the above-mentioned high frequency circuit, the frequency band characteristic thereof is easily influenced by the high frequency grounding capacitance Cg, and in applications requiring a wide operating frequency band, desired characteristics can be obtained within that band. There is a problem that you can not do it.

FIG. 7 is a graph showing the relationship between the operating frequency and the conversion gain of the high frequency conversion circuit shown in FIG. 6. As shown by the curve A in the figure, when the high frequency ground capacitance Cg is small, The conversion gain decreases in the lower frequency region, and conversely, as indicated by the curve B in the figure, the high frequency ground capacitance C
If g is large, the conversion gain will decrease in the higher frequency region. For this reason, in applications such as BS chargers that require a wide operating frequency band, it has been difficult to ensure constant characteristics over the entire band.

It is an object of the present invention to provide a technique for ensuring the characteristics of a high frequency circuit over a wide operating frequency band.

The above and other objects and characteristics of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0011]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

That is, a high frequency signal is input to one input terminal of a high frequency circuit having a pair of balanced input terminals, and the other input terminal is connected to a high frequency grounding capacitance,
A variable capacitance element is included in the high frequency ground capacitance.

[0013]

According to the above-mentioned means, by varying the capacitance value of the high frequency grounding capacitance according to the operating frequency, it is possible to avoid or reduce the influence of the capacitance value of the high frequency grounding capacitance on the frequency band characteristic.

This achieves the object of ensuring the characteristics of the high frequency circuit over a wide operating frequency band.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 shows an embodiment of a high frequency circuit to which the technique of the present invention is applied.

The high frequency circuit shown in the figure is applied to a high frequency conversion circuit for a BS tuner, and 1 is a balanced mixer circuit in which two differential circuits of transistors are cascade-connected in series, 11, 12 is an RF (high frequency) input terminal, Cg is a high frequency ground capacitance, and 13 and 14 are L
o (local signal) input terminal, 2 is an IF (intermediate frequency) output circuit, and 21 is an IF output terminal.

RF input terminals 11 and 12 of the mixer circuit 1
A high-frequency signal is input to one of the two (11) and a high-frequency grounding capacitance Cg is connected to the other (12).

The high frequency ground capacitance Cg is formed by a composite capacitance circuit including a fixed capacitance C1 interposed in parallel with the input terminal 12, a fixed capacitance C2 interposed in series, and a variable capacitance element Cv interposed in parallel. .

A so-called varicap diode is used as the variable capacitance element Cv, and its capacitance value is electrically variably set by a control voltage VC applied from the outside through a resistor R1.

Next, the operation will be described.

In the high frequency circuit shown in FIG. 1, the operating frequency band characteristic changes depending on the high frequency grounding capacitance Cg, but the capacitance value of the high frequency grounding capacitance Cg depends on the external control voltage VC as described above. It can be electrically variably controlled.

Therefore, when the operating frequency band is wide,
By varying the capacitance value of the high frequency grounding capacitance Cv by the control voltage VC that is variably set according to the operating frequency, the capacitance value of the high frequency grounding capacitance Cg can be always brought to the optimum condition.

As a result, as shown by the curve C in FIG.
It is possible to avoid or mitigate the influence of the high frequency ground capacitance Cg on the frequency characteristic, and to secure a predetermined characteristic over a wide operating frequency band.

FIG. 3 shows a configuration example of a high frequency conversion circuit including a supply source of the control voltage VC.

In the figure, the control voltage VC is obtained from the oscillation frequency control voltage VC generated in the PLL (phase control loop) which constitutes the local oscillator 3.

That is, the local oscillator 3 is composed of a VCO (voltage controlled oscillator) 31 and a PLL control circuit 32. The control voltage VC fed back from the PLL control circuit 32 to the VCO 31 is a high frequency ground capacitance Cg of the mixer circuit 1. The control voltage VC is also applied to the control voltage VC.

As a result, the composite capacitance circuit forming the high frequency ground capacitance Cg is variably controlled in conjunction with the operating frequency of the mixer circuit 1, and the operating frequency band can be expanded with a simple structure. Become.

FIG. 4 shows an embodiment in which the high frequency circuit of the present invention is applied to the high frequency amplifier circuit 4.

As shown in the figure, the high frequency amplifier circuit 4 used in the frequency region such as a BS tuner is often of a transistor differential circuit type, and one side of its balanced input terminal has a high frequency ground capacitance Cg. Often connected to.

Also in this case, by including a variable capacitance element such as a varicap diode in the high frequency grounding capacitance Cg, the influence of the high frequency grounding capacitance Cg on the frequency characteristics can be avoided or mitigated, and a predetermined operating frequency band can be obtained. It is possible to secure the characteristics of.

FIG. 5 is a circuit diagram of the circuit shown in FIGS.
4 shows a schematic configuration of a BS tuner configured using 4).

In the figure, 101 is a BS antenna, 4
Is a high frequency amplifier circuit, 102 is a high frequency BPF (RF band pass filter), 103 is an attenuator, 1 is a mixer circuit, 3 is a local oscillator, and 104 is an intermediate frequency BPF (R
F band pass filter), 105 is an intermediate frequency amplifier circuit, 1
Reference numeral 06 is an FM demodulation circuit, 107 is a video circuit, and 108 is an audio circuit.

The BS tuner is required to have constant characteristics over a very wide operating frequency band, but the use of the circuit (1, 4) described above results in stable characteristics over the entire wide operating frequency band. Good broadcast reception is possible.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, the variable capacitance element Cv may be such that the number of connections of a plurality of capacitance elements is switched by a diode switch or the like.

In the above description, the case where the invention made by the present inventor is mainly applied to the receiving circuit which is the background field of application has been described, but the present invention is not limited to this, and may be applied to the transmitting circuit, for example. Applicable.

[0039]

The effects of the typical ones of the inventions disclosed in this application will be briefly described as follows.

That is, the characteristics of the high frequency circuit can be secured over a wide operating frequency band.
The effect is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a high frequency circuit to which the technique of the present invention is applied.

FIG. 2 is a graph showing frequency characteristics obtained by the high frequency circuit according to the present invention.

FIG. 3 is a circuit diagram showing a main part of a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing an essential part of a third embodiment of the present invention.

FIG. 5 is a block circuit diagram showing a schematic configuration of a BS tuner using the present invention.

FIG. 6 is a circuit diagram showing an outline of a conventional high frequency circuit.

FIG. 7 is a graph showing frequency characteristics obtained by a conventional high frequency circuit.

[Explanation of symbols]

 1 mixer circuit (high frequency circuit) 11,12 RF (high frequency) input terminal Cg high frequency grounding capacitance 13,14 Lo (local signal) input terminal 2 IF (intermediate frequency) output circuit 21 IF output terminal Cv variable capacitance element VC control voltage 3 Local oscillator 31 VCO (voltage controlled oscillator) 32 PLL control circuit 4 High frequency amplifier circuit

Claims (2)

[Claims] 1. A high-frequency circuit having a balanced input terminal, wherein a high-frequency signal is input to one of the balanced input terminals,
A high-frequency circuit characterized in that the other is connected to a high-frequency grounding capacitance and the high-frequency grounding capacitance includes a variable capacitance element. 2. A high frequency circuit having a balanced input terminal, wherein a high frequency signal is input to one of the balanced input terminals,
A high-frequency circuit, characterized in that the above-mentioned high-frequency grounding capacitance is constituted by a capacitance circuit which is variably controlled in conjunction with an operating frequency while connecting the other to a high-frequency grounding capacitance.