JPS60233906A - Oscillating circuit - Google Patents

Abstract

PURPOSE:To attain ease of adjustment after manufacture of an oscillating circuit by controlling electrically a capacitance value of a feedback capacitive element provided between an emitter and a collector of a transistor (TR). CONSTITUTION:The capacitance value of the feedback capacitive element connected between the emitter and collector of the oscillating circuit having a common base TR2 is effected largely by the noise characteristic of the oscillating circuit. Then the capacitance value of the feedback capacitor connected between the emitter and collector is made variable and the capacitance value is adjusted after the manufacture of the oscillating circuit. In order to make the capacitance value variable, for example, a series circuit comprising a capacitive element 14 and a varactor element 13 is used. The anode of the varactor element 13 is connected to the collector of the TR2 and the cathode is connected to a terminal 16 via a high frequency blocking coil 15. The feedback capacitance value is controlled electrically by adjusting the bias fed to the terminal 16.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to VHF and UHF band transmitters/receivers, particularly highly stable oscillation circuits required in mobile communications, such as frequency synthesizers that are local oscillators in car phones, etc. This invention relates to oscillator circuits that require high stability and low noise, such as oscillators.

Conventional Structures and Problems Commonly used as oscillators in the VHF and UHF bands, common base type transistor oscillation circuits are often used in view of noise and frequency stability.

Hereinafter, a conventional grounded base type oscillation circuit will be explained with reference to FIG.

In FIG. 1, 1 is a resonant line used as an inductive element, 2 is a transistor which is an active element, and feedback capacitors 3 and 4 are arranged between the terminals thereof, respectively. Also, each terminal bias of transistor 2 is controlled by resistor element 5.6.
．． 7. This is done by high frequency blocking coils 8 and 9. 1
o is a power supply voltage supply terminal. 11 is a capacitive element having a value that is bypassed at high frequencies. 12 is a coupling capacitance element between the resonance line 1 and the transistor 20 circuit side.

In the above configuration, the conditions for reducing the noise of the high-frequency transistor oscillation circuit are to realize a high no-load Q of the resonant line 1, to employ a low-noise transistor 2, and to place the low-noise transistor 2 between the terminals of the transistor 2. Optimization of the feedback capacitance 3 between the collector and emitter terminals and the feedback capacitance 4 between the emitter and ground are important factors.

Generally, the essential circuit condition for an oscillation circuit is the coupling capacitance 1
2) When looking at the impedance on the transistor side (indicated by zT in Figure 1), it must have a negative impedance, and the level of that impedance determines the stability of the oscillation circuit, and then Affects noise characteristics.

Optimization of the feedback capacitance, which is one of the factors for the low noise mentioned above, is due to this.

In particular, among the two feedback capacitances, the feedback capacitance 3 between the collector and emitter has a remarkable influence.

Figure 2 shows the extent to which the H
This is the FM sideband noise characteristic evaluated using the current noise.

As shown in Figure 2, the degree of noise changes depending on the installed capacitance value, and if the capacitance value changes by o or spF, the noise decreases by 1.
．． It varies from 6 to 2.5 dB.

In this way, the feedback capacitor 3 is extremely sensitive to noise. If the capacitance value of the capacitor attached thereto varies during manufacturing, it has the disadvantage of causing deterioration of noise characteristics. Further, this device capacitance 3 is also an important part in an oscillation circuit that can correct some deterioration in characteristics caused by bias fluctuations due to variations in resistance elements. The problem can be solved by replacing the capacitor parts during post-manufacturing adjustments, or by suppressing variations in the capacitors used in advance and using limited parts, but these reduce manufacturing efficiency and are not economical. do not have.

OBJECTS OF THE INVENTION In view of the above-mentioned drawbacks, the present invention provides an economical oscillation circuit that is simple and labor-saving in the adjustment process after manufacturing.

Structure of the Invention As described above, the present invention comprises an oscillation means having a pace-grounded transistor, a feedback capacitance means provided between the emitter and collector terminals of the transistor and having at least a variable capacitance element, and a feedback capacitance means of the feedback capacitance means. The above object is achieved by providing capacitance value control means for electrically controlling the feedback capacitance value.

DESCRIPTION OF THE EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows the circuit configuration of the oscillation circuit in the first embodiment of the present invention.

In FIG. 3, 1 is a resonant line using an inductive element, one end of which is grounded. 2 is a base-connected type transistor which is a power element, 4 is a feedback capacitor element of transistor 2, 5, 6.7 are resistors which are bias elements of transistor 2, and 8 and 9 are bias elements of transistor 2. A coil for high frequency blocking, 10 a terminal to which a power supply voltage is applied, 11 a capacitive element having a capacitance bypassed at high frequencies, and 12 a coupling capacitive element between the resonant line 1 and the circuit side of the transistor 2.

The above resonant line 1, transistor 2, feedback capacitive element 4,
The resistors 5, 6, 7, coils 8, 9, and capacitive elements 11, 12 are similar to the conventional structure shown in FIG.

The difference from the configuration shown in FIG.
2. According to the above configuration, the fixed capacitor 3 shown in FIG. Feedback capacitance element 13 and varactor element 14 fixed to
is placed between the collector and emitter terminals of the transistor 2, and one end of the varactor element 14 is connected to the transistor 2.
The anode is connected to the collector terminal of the transistor 2 (the anode is connected to the collector terminal of the transistor 2), and the other end is configured so that bias can be supplied to the terminal 16 independently via the high frequency blocking coil 15. The capacitance between can be electrically controlled.

Note that in this embodiment, the capacitive element circuit was constructed by connecting the fixed feedback capacitive element 13 and the varactor element 14 in series, but these are not limited to being connected in series, but may be connected in series and parallel, for example. .

In addition, if the capacitance change width between the collector and emitter terminals of the transistor 2 is to be increased, a plurality of varactor elements 17 and 18 are used as shown in FIG. do it.

Effects of the Invention As described above, the present invention can reduce the number of man-hours for adjustment etc. in the manufacturing work of an oscillation circuit, and furthermore, it leads to lower noise, is simple, and has great industrial value.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional oscillation circuit, FIG. 2 is a characteristic diagram showing FM sideband noise characteristics in the same circuit, and FIGS. FIG. 3 is a circuit configuration diagram of an oscillation circuit in a second embodiment. 1... Resonance line, 2... Transistor, 4 and 14... Feedback capacitive element, 6, 6 and 7
...Resistance, 8.9 and 15 ... Coil, 11, 12 ... Capacitive element, 14.17 and 1
8...Varactor element. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 f@mma resistance @ (kHl) Figure 3

Claims (4)

[Claims] (1) An oscillation means having a common base type transistor, a feedback capacitance means provided between the emitter and collector terminals of the transistor and having at least a small number of variable capacitance elements, and a feedback capacitance value of the feedback capacitance means. An oscillation circuit comprising electrically controlled capacitance value control means. (2) The oscillation circuit according to claim 1, wherein the feedback capacitance means is constituted by a series or series-parallel circuit of a fixed capacitance element and a variable capacitance element. (3) The oscillation circuit according to claim 1, wherein the variable capacitance element is a varactor element. (4) The oscillation circuit according to claim 1, wherein the feedback capacitance means is a series circuit of a plurality of varactor elements. 2. The oscillation circuit according to claim 1, wherein the capacitance value control means is configured to apply a voltage to the variable capacitance element via a high frequency blocking coil.