JPS6040725B2 - oscillation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a UHF band oscillation device that can keep the output voltage of the oscillation frequency constant over a wide band.

An example of a UHF band input/4 type oscillation circuit is shown in FIG.

This oscillation circuit includes an oscillation transistor, a resonant line 2 forming a resonant circuit that determines the oscillation frequency, a variable capacitor 3, a fixed capacitor 4, a feedback capacitor 16, DC bias resistors 7, 8, 9, and a drive power terminal 10. , a high frequency choke coil 11, and a tuning voltage supply terminal 13 that applies voltage to the variable capacitance element 3 through a high resistor 12. In the oscillation circuit shown in FIG. 1, FIG. 2 shows the relationship between the oscillation output voltage and the oscillation frequency when the tuning voltage applied to the terminal 13 is varied.

As shown in FIG. 2, as the tuning voltage decreases and the oscillation frequency decreases, the oscillation output voltage decreases or oscillation stops. When the value of the feedback capacitor 6 is increased, the change from a to b in Fig. 2
Turning to the characteristics, although the above phenomenon is improved, the maximum oscillation frequency decreases due to the increase in resonant capacitance, making it difficult to put it into practical use in the case of a UHF tuner that requires an oscillation frequency over a wide band. As described above, in the case of the configuration shown in FIG. 1, it is difficult to keep the oscillation output voltage constant over a wide band. The present invention eliminates the above-mentioned drawbacks and provides a UHF band oscillator whose oscillation output voltage is constant over a wide band.

An embodiment of the present invention will be described in detail below.

FIG. 3 shows an embodiment of the present invention, in which parts having similar functions to those in FIG. 1 are given the same numbers.

The difference from FIG. 1 is that an inductance 14 and a resistor 15 are connected to the collector of the oscillation transistor 1. In the conventional example shown in FIG. 1, the outside of the oscillating transistor 1 has almost the same potential as the anode side point a of the variable capacitance element 3, and if the capacitance value of the variable capacitance element 3 is denoted by Cd, then the Q value of the resonant circuit is is inversely proportional to Cd.

Therefore, when Cd is increased to lower the oscillation frequency, the Q value of the resonant circuit decreases and the oscillation output voltage decreases. On the other hand, in the circuit shown in FIG. Since the value of is determined, the impedance at the collector of the oscillation transistor changes as shown in FIG. Here, a indicates the conventional circuit, and b indicates the circuit of the present invention. That is, the impedance at the oscillation frequency becomes large in the circuit of the present invention. Therefore, since this impedance is larger than in the conventional example, the oscillation output voltage does not decrease as seen in the conventional example, and the characteristics are improved as shown in FIG. In FIG. 5, a is the conventional case, and b is the present invention. Note that the resistor 15 is used to optimize the impedance at the collector. FIG. 6 shows another embodiment of the present invention, in which a diode (for example, a PIN diode) shown in the equivalent circuit of FIG. 7 is used as the inductance 14 and resistor 15 on the collector side.

Parts that have the same function as those in Figure 3 are given the same numbers. The diode 16 in FIG. 6 is as shown in the equivalent circuit in FIG.
Since it is represented by a series inductance LS and a series resistance ys, it operates in the same way as the inductance 14 and resistor 15 in FIG. 3, and as a result, the characteristics shown in FIG. 5 can be realized. If a diode with the equivalent circuit shown in Figure 7 is connected in place of the inductance and resistor, this diode 16 is the only component that determines the resonant frequency of the collector resonant circuit, making it easy to reduce variations in the resonant frequency. It also becomes much easier to make the oscillation output voltage uniform. As described above, according to the present invention, the inductance 1 on the collector side of the oscillation transistor is set so that the oscillation transistor resonates at a frequency slightly lower than the oscillation frequency.
4 and a resistor 15, or by using a diode 16 that has a similar effect, the impedance on the collector side is prevented from decreasing, the oscillation output voltage is prevented from decreasing, and the oscillation output voltage is made uniform over a wide band. can be realized.

As a result, the noise figure has improved significantly, especially in the low frequency channels of electronically tuned tuners in the UHF band.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram of a conventional UHF band oscillation circuit, Fig. 2 is a diagram showing the oscillation output voltage characteristics of the conventional example, Fig. 3 is a circuit diagram showing an oscillation device in an embodiment of the present invention, and Fig. 4 is a diagram explaining the operation of the present invention, FIG. 5 is a characteristic diagram of one embodiment of the present invention, FIG. 6 is a circuit diagram showing another embodiment of the present invention, and FIG. 7 is a diagram of a diode used in the present invention. It is an equivalent circuit diagram. 1...Transistor, 3...Variable capacitance diode, 14...Inductance, 15...
・Resistance, 16...diode. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1. An oscillation device characterized in that a parallel resonant circuit having a resonant frequency slightly lower than the oscillation frequency is provided on the collector side of an oscillation transistor. 2. The oscillation device according to claim 1, wherein the parallel resonant circuit is constructed using a diode that can be equivalently represented by an inductance and a resistor.