JPH01280903A - Frequency variable tuning circuit - Google Patents

Abstract

PURPOSE:To improve the linearity of the frequency variable characteristic with respect to the impressed voltage by providing a characteristic different from the capacitance change characteristic with respect to the impressed voltage for the varactor diode. CONSTITUTION:The characteristic of a differentiating coefficient of a varactor diode CV1 is selected to be a characteristic having a peak at a low impressed voltage VL and the differentiating characteristic of a varactor diode CV2 is selected to be a characteristic having a peak at a high impressed voltage VH, then the synthesis characteristic of the varactor diodes CV1, CV2 has a characteristic having a high differentiating coefficient both for low and high voltages. Thus, the differentiating coefficient with respect to the impressed voltage is made more flat over the wide range in comparison with a tuning circuit using only the varactor diodes CV1, CV2. Thus, the linear range of the tilt in the capacitance change per unit impressed voltage is extended and the linearity of frequency fluctuation with respect to the impressed voltage is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable frequency tuning circuit used in high frequency equipment, and particularly to a tuning circuit using a variable capacitance diode.

[Conventional technology]

Conventionally, this type of frequency variable tuning circuit has a configuration in which a plurality (n) of variable capacitance diodes used for the tuning function are connected in parallel with the same applied voltage and capacitance change characteristics, and the series resistance of these diodes is r S
/n, and is used as a method to improve the quality factor Q of a tuning circuit. In addition, Q=ωL/r
, where ω is the angular frequency, L is the inductance of the tuned circuit, and r is the resistance of the tuned circuit.

[Problem to be solved by the invention]

In the conventional frequency variable tuning circuit described above, the Q of the tuning circuit is
However, there is a drawback that the linearity of frequency variation with respect to applied voltage cannot be improved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a frequency variable tuning circuit which eliminates such drawbacks and improves the linearity of frequency variable characteristics with respect to applied voltage.

[Means to solve the problem]

The structure of the present invention is characterized in that, in a frequency variable tuning circuit configured by connecting a plurality of variable capacitance diodes in parallel, the variable capacitance diodes have different capacitance change characteristics with respect to applied voltage. do.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, showing an input frequency tuning circuit in a high frequency amplifier circuit of transistor Q+. The frequency variable input tuning circuit includes two variable capacitance diodes CVI and CV2, a capacitor C2,
A tuning voltage is applied to this circuit from a frequency voltage application terminal VTu via a resistor R.

The input signal is input from the input terminal RFIN, and is connected to the inductance L of the tuned circuit via the capacitor CI + C3.
1 and is supplied to the base of the transistor Q1 of the high frequency amplification circuit. The base of this transistor Q1 is supplied with a bias voltage divided by a resistor R2 and a resistor R5 from the power supply terminal ■cc, and its emitter is supplied with a bias voltage divided by a resistor R4.
, a capacitor C4 is connected to the collector thereof, a high frequency choke coil L2 is connected from the power supply terminal VCC to the collector thereof, and an output signal is outputted from the output terminal RFour via the capacitor C5.

Figures 2 (a) and (b) show the characteristics of a variable capacitance diode. Figure 2 (a) shows the characteristics of the applied voltage ■8 vs. is shown in Figure 2 (
The applied voltage V with the characteristics of a>.

It shows the change characteristics of the slope (differential coefficient) of capacitance change with respect to

The characteristic of the differential coefficient of the variable capacitance diode CV of this embodiment is set to have a peak at a low applied voltage VL, as shown in FIG. As shown in Figure (b), when the characteristics have a peak at high applied voltage VH, these variable capacitance diodes C
The composite characteristic of vl and Cv2 has a high differential coefficient for both low voltage and high voltage, as shown in FIG. 3(c).

Therefore, compared to a tuned circuit using only the variable capacitance diode CV or CV2, the differential coefficient with respect to the applied voltage becomes flat over a wide range, and the linear region range of the slope of capacitance change per unit of applied voltage is expanded. This makes it possible to improve the linearity of frequency fluctuations with respect to applied voltage.

FIG. 4 is a circuit diagram of a second embodiment of the present invention, showing a variable frequency tuning circuit in which a common emitter transistor Q2 constitutes a high frequency oscillation circuit. The oscillation circuit consists of transistor Q21 bias resistors R2, R4, and base resistor R.
3. The L-type tuned circuit consists of a capacitor C3 and a choke coil L2, and the L-type tuning circuit is a variable capacitance diode Cv 1 +
CV 21 The tuning voltage is applied to the tuning voltage application terminal V through the capacitor C2 and inductance L3, and the resistor R5.
The oscillation output is output from the output terminal ○SC via the inductance Ll and the capacitor C1.

In this case, as in the first embodiment, by using variable capacitance diodes with different capacitance variable characteristics for the variable capacitance diodes Cvl and Cy2, it is possible to expand the linear region of the slope of the capacitance change per unit of applied voltage. can.

〔Effect of the invention〕

As explained above, the present invention uses a frequency variable circuit in which variable capacitance diodes with different capacitance change characteristics with respect to applied voltage are connected in parallel, thereby reducing the series resistance component of the diodes and reducing the slope of capacitance change per unit of applied voltage. The linear region range can be expanded, and the linearity of the tuning frequency fluctuation rate with respect to applied voltage fluctuations, ambient temperature fluctuations, etc. can be improved over a wide range.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2(a), (
b) is the capacitance characteristic diagram and differential coefficient characteristic diagram with respect to the applied voltage of the variable capacitance diode, Figure 3 (a), (b), (c
) are the two variable capacitance diodes Cv 1 used in Figure 1.
, Derivative coefficient characteristic diagram of Cy2 and its combination, 4th
The figure is a circuit diagram of a second embodiment of the present invention. 01-C5... Capacitor, CVl, CV2... Variable capacitance diode, L, , R3... Inductance,
R2...High frequency choke coil, Ql, Q2...Transistor, R1-R4...Resistor, ○SC...Oscillation output terminal, RF IN, RF out -RF input terminal, ■cc...Power supply terminal , VT (1... Tuning voltage application terminal.

Claims (1)

[Claims] A frequency variable tuning circuit configured by connecting a plurality of variable capacitance diodes in parallel, wherein the variable capacitance diodes have different capacitance change characteristics with respect to applied voltage.