JPH0224256Y2 - - Google Patents

Description

[Detailed description of the invention] The purpose of this invention is to minimize the difference in oscillation circuit control sensitivity voltage between the lower limit oscillation frequency and the upper limit oscillation frequency in a voltage controlled oscillation circuit using a variable capacitance diode. This relates to voltage controlled oscillation circuits.

Conventionally, the resonant circuit of a wideband voltage controlled oscillator circuit has been constructed of a single variable capacitance diode and a switchable fixed capacitor, and the upper and lower limits of the oscillation frequency have been switched by switching the fixed capacitor.

In conventional circuits that change the fixed capacitance value, the oscillation circuit control sensitivity voltage at the upper and lower limits for the same control voltage is different, so it is necessary to use the lower limit frequency where the upper and lower bandwidths are narrow, that is, the frequency change with respect to changes in the control voltage is small. If the oscillation circuit is designed to have a large bandwidth, the bandwidth will be unnecessarily wide at the upper limit frequency, which means that the frequency will change greatly even with a small change in the control voltage, and the C (carrier)/N of the oscillation circuit will increase. (noise) characteristics were worsening.

The present invention has been made to improve the conventional drawbacks as described above, and in a voltage controlled oscillator using a variable capacitance diode, another variable capacitance diode is added to the variable capacitance diode,
By selectively switching between one, two in parallel, two in series, etc. using a switching circuit, the difference between the upper and lower limits is eliminated over a wide band.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 1, reference numeral 1 denotes a so-called Colpitts-type oscillation circuit with a common base and composed of a transistor 2 and capacitors 3 and 4. An output terminal 6 is connected to the output side of this oscillation circuit 1 via a coupling capacitor 5.
A resonant circuit 13 consisting of a microstrip line 7, capacitors 8, 9, and 10, and variable capacitance diodes 11 and 12 is also coupled to the input side. In this resonant circuit 13, one series circuit of a fixed capacitance capacitor 9 and a variable capacitance diode 11, and the other series circuit of a fixed capacitance capacitor 10 and a variable capacitance diode 12 are connected to each other via a switching diode 14. connected in parallel. Further, the connection points between these capacitors 9 and 10 and variable capacitance diodes 11 and 12 are connected to high frequency choke coils 15 and 1, respectively.
6 to a control voltage input terminal 17. In addition, 18 and 19 are high frequency choke coils,
20, 21, and 22 are high frequency bypass capacitors.

23 is a switching circuit that turns on and off the switching diode 14, and connects the diode 14 from the power supply terminal (+B) through the PNP type first transistor 24 and the chiyoke coil 18.
is connected to the cathode side of the power supply terminal (+
B) to the diode 14 via the NPN type second transistor 25 and the yoke coil 19.
is connected to the anode side of the In addition, 26 is a changeover switch that can be changed depending on the frequency band.
This changeover switch 26 has, for example, a reception contact 27 and a transmission contact 28, and the reception contact 27 is coupled to the power supply terminal (+B) via a resistor 29, and the first and second contacts are connected via resistors 30, 31, and 32, respectively. It is coupled to the bases of the second and third transistors 24, 25, 33, and a common contact 34 is grounded. The collector of the third transistor 33 is coupled to the cathode of the diode 14 via the resistor 35 and the choke coil 18, and the emitter is grounded.

Next, the operation of the circuit according to the present invention will be explained. When receiving a high carrier signal frequency, switch 2
6 to the receiving contact 27, the first transistor 24 is turned on and the second and third transistors 2
5 and 33 are turned off. Therefore, a reverse voltage is applied to the switching diode 14, and the capacitor 9
and the variable capacitance diode 11 is disconnected. Therefore, the frequency of the resonant circuit is determined by the microstrip line 7, the capacitors 8 and 10, and the variable capacitance diode 12, and the range of capacitance change due to the control voltage from the input terminal 17 is narrowed, which increases the oscillation circuit control sensitivity voltage. Make it smaller.

Next, when transmitting a low carrier signal frequency, the changeover switch 26 is coupled to the transmission contact 28. Then, the first transistor 24 is turned off, and the second and third transistors 25 and 33 are turned on. Therefore, the switching diode 14 is turned on by the forward voltage applied through the second transistor 25, and the capacitors 9 and 10 and the variable capacitance diodes 11 and 12 are coupled in parallel with each other, and thus, Equivalently, the capacitance change width is widened and the oscillation circuit control sensitivity voltage is increased.

Next, FIG. 2 shows another embodiment of the present invention, in which capacitors 9 and 10 and variable capacitance diodes 11 and 12 are all inserted in series.
Switching is performed using an intermediate switching diode 14. More specifically, during reception, when the changeover switches 26a, 26b, 26c are switched to the reception contacts 27a, 27b, 27c, the switching diode 14 is turned on, and the capacitors 9, 10 and variable capacitance diodes 11, 12 are all connected in series. This reduces the width of capacitance change and reduces the oscillation circuit control sensitivity voltage. During transmission, when the transmission contacts 28a, 28b, and 28c are switched, the capacitor 10 and the variable capacitance diode 12 are separated, widening the capacitance change range and increasing the oscillation circuit sensitivity voltage.

Since the present invention is configured as described above, when the oscillation frequency is varied over a wide range, the difference in the oscillation circuit control sensitivity voltage between the upper limit frequency and the lower limit frequency can be made as small as possible. In other words, the change in frequency with respect to the change in the control voltage of the variable capacitance diode can be made substantially constant at both the upper and lower limits, and therefore the C (carrier)/N (noise) characteristics can be improved.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing one embodiment of a voltage controlled oscillation circuit according to the present invention, and FIG. 2 is an electric circuit diagram of another embodiment of the present invention. 1...Oscillation circuit, 2...Transistor, 3,
4, 5... Capacitor, 6... Output terminal, 7...
Microstrip line, 8, 9, 10... capacitor, 11, 12... variable capacitance diode,
13... Resonance circuit, 14... Switching element (diode), 15, 16, 18, 19... Chi York coil, 17... Control voltage input terminal, 20,
21, 22... Capacitor, 23... Switching circuit,
24, 25, 33...transistor, 26, 26
a, 26b, 26c...changeover switch, 27,2
7a, 27b, 27c...reception contact, 28, 28
a, 28b, 28c...transmission contact, 29, 30,
31, 32...Resistance.

Claims (1)

[Scope of utility model registration request] A wideband voltage in which the capacitance of a first variable capacitance diode of a resonant circuit consisting of a microstrip line, a capacitor, and a variable capacitance diode coupled to an oscillation circuit is varied by a control voltage, and the oscillation frequency is varied. In the controlled oscillation circuit, in addition to the first variable capacitance diode and capacitor for high frequencies, a second variable capacitance diode and capacitor are added in parallel for low frequencies, and these first and second variable capacitors A switching element consisting of a diode is inserted between the diodes, the first variable capacitance diode and capacitor for high frequency are selected in the switching element when the switching element is off, and the first and second variable capacitors are selected when the switching element is on. 1. A voltage controlled oscillation circuit comprising two variable capacitance diodes and a capacitor coupled in parallel to each other and a switching circuit for coupling the oscillation circuit to the oscillation circuit.