JPH0545083B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a local oscillation circuit that can be used in television receivers and the like.

BACKGROUND OF THE INVENTION In recent years, equipment using high frequencies in the video field has developed greatly, and in particular, circuits up to several GHz bands have made remarkable progress, and various improvements have been made to local oscillation circuits.

FIG. 2 shows a conventional local oscillation circuit, in which 31 is an oscillation transistor, 32 is a bias resistor, 33 is a bypass capacitor, 34 is a coupling capacitor, 35 is a variable capacitance diode, 36 is a resonator, 37 is a bias resistor, 38 is a bypass capacitor, 39 is a chiyoke coil, 40 is a damping resistor, 41 is a coupling capacitor, 4
2 is an amplification transistor, 43 is a bias resistor,
44 is a coupling capacitor, 45 is a choke coil, and 46 is a bypass capacitor. 2A is the tuning voltage terminal, 2
B and 2D are positive power supply terminals, and 2C is an oscillation output terminal. If the collector of the oscillation transistor 31 is grounded in an alternating current manner, the impedance seen from the base becomes negative. Here is the variable capacitance diode 35
A series resonant circuit consisting of a resonator 36 and a coupling capacitor 3
4 and the other end is grounded, this circuit has the amplitude characteristics of the resonant circuit and the negative gain of the transistor of 1 or more, and the sum of the negative phases of the resonant circuit and the transistor is 2nπ (n is an integer). ) oscillates at a frequency that satisfies the conditions. If a tuning voltage is applied here from the tuning voltage terminal 2A via the bias resistor 37,
Since the capacitance changes according to changes in the reverse bias potential of the variable capacitance diode, the oscillation frequency can be varied. This signal is transmitted to the chiyoke coil 39
is taken out from the emitter and supplied to the amplification transistor 42 via the coupling capacitor 41, where it is amplified and passed through the coupling capacitor 44 to obtain an oscillation output from the oscillation output terminal 2C. Power is applied to the collector of the amplification transistor 42 from the positive power supply terminal 2D via a chiyoke coil 45. (For example, JP-A-59-149405
Problems to be Solved by the Invention In such a conventional configuration, the current of the oscillation transistor changes greatly as the oscillation frequency changes, and the transistor becomes saturated in a region where a large current flows, especially near the minimum oscillation frequency. However, there was a drawback that the operation became unstable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a local oscillation circuit that can reduce changes in the operating current of an oscillation transistor even if the oscillation frequency changes.

Means for Solving the Problems In the local oscillation circuit of the present invention, the collector of the first transistor is grounded in an AC manner, a series resonant circuit consisting of a variable capacitance diode and a resonator is connected to its base, and the other end is connected to the AC ground. The emitter of the first transistor is connected to the collector of the second transistor whose emitter is grounded through a load circuit that removes or reduces the alternating current component and passes the direct current component. An oscillation signal taken out from the emitter of the first transistor is connected to the base in an alternating current manner, a local oscillation output signal is taken out from the collector of the second transistor, and a bias potential is connected to the power supply or the second transistor.
The characteristic is that the voltage is applied from the collector of the transistor.

Effects According to this configuration, the operating current of the circuit is determined by the second transistor, so even if the oscillation frequency changes, the operating current does not change significantly.

Embodiment Hereinafter, an embodiment of the present invention will be described based on FIG.

FIG. 1 shows a local oscillator circuit of the present invention. 11 is an oscillation transistor, 12 is a bias resistor, 13
is a bypass capacitance, 14 is a coupling capacitance, 15 is a variable capacitance diode, 16 is a resonator, 17 is a bias resistor, 18 is a bypass capacitor, 19 is a chiyoke coil, 20 is a damping resistor, 21 is a coupling capacitor, and the above 11- 21 are respectively 31~ in Figure 2
This is similar to 41. 22 is an amplification transistor, 23 is a bias resistor, 24 is a coupling capacitor, 1
A is tuning voltage terminal, 1B is positive power supply terminal, 1C
is the oscillation output terminal.

11 to 2 including the oscillation operation of the local oscillation circuit configured in this way and the oscillation transistor 11
The configurations and operations up to 8 are the same as those described in the conventional example, so their explanations will be omitted. A chiyoke coil 19 is connected to the emitter of the oscillation transistor 11.
are connected, and the oscillation output is taken out from the intersection via the coupling capacitor 21. The choke coil 19 is connected to the collector of a constant current/amplification transistor 22 via a damping resistor 20. Due to this choke coil 19, the oscillation output is not directly supplied to the collector of the transistor 22, and no signal is transmitted.
is supplied to the base of transistor 22 via
Here, the amplified output is supplied from the collector to the next stage via the oscillation output terminal 1C. The bias of the transistor 22 is the positive power supply terminal 1
B to the base via the bias resistor 23. Even if this bias is applied from the collector of the transistor 22 through the bias resistor 23, the constant current effect is somewhat reduced, but the effect remains.

By providing a constant current circuit at the emitter of the oscillation transistor 11 in this manner, current changes due to changes in the oscillation frequency can be reduced without increasing the operating current and unnecessary circuits.

Note that since the purpose of the chiyoke coil 19 and the resistor 20 as a load circuit is to remove high frequencies, either one of them may be used.

Effects of the Invention As explained above, the local oscillation circuit of the present invention connects the emitter of the first transistor for oscillation to a second transistor whose emitter is grounded via a load circuit that removes or reduces the alternating current component and passes the direct current component. Since the second transistor is connected to the collector of the second transistor and operated at a constant current, changes in current due to changes in the oscillation frequency can be reduced, and stable oscillation operation can be obtained.

Furthermore, the oscillation signal extracted from the emitter of the first transistor is connected to the base of the second transistor in an alternating current manner, and the local oscillation output signal is extracted from the collector of the second transistor, which reduces the number of parts in the circuit compared to conventional methods. The operating current can also be reduced at the same time, and the same or higher performance can be ensured.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the local oscillation circuit of the present invention, and FIG. 2 is a block diagram of a conventional circuit. 11... Oscillation transistor, 12... Bias resistor, 13... Bypass capacitor, 14... Coupling capacitor, 15... Variable capacitance diode, 16... Resonator, 17... Bias resistor, 18... Bypass capacitor, 19... Chi York coil, 20... Damping resistor, 21... Coupling capacitance, 22... Amplifying transistor, 23... Bias resistor, 24... Coupling capacitance, 1B... Plus power supply terminal, 1A... Tuning voltage terminal, 1C...Oscillation output terminal.

Claims (1)

[Claims] 1 The collector of the first transistor is grounded in an alternating current manner, a series resonant circuit consisting of a variable capacitance diode and a resonator is connected to its base, the other end is grounded in an alternating current manner, and the emitter of the first transistor is connected to an alternating current component. The emitter is connected to the collector of a second transistor whose emitter is grounded through a load circuit that removes or reduces the DC component and passes the DC component, and the oscillation signal extracted from the emitter of the first transistor is connected to the base of the second transistor. A local oscillation circuit connected in an alternating current manner, extracting a local oscillation output signal from the collector of a second transistor, and applying a bias potential to the second transistor from a power supply or the collector of the second transistor.