Oscillator including a transistor used both as constant current

Details Oscillator including a transistor used both as constant current Oscillator including a transistor used both as constant current

1987-04-10

1989-01-10

Grimm, Siegfried H.

Oscillators

Solid state active element oscillator

Transistors

331177V, H03B 518, H03B 512

Patent

active

047976381

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Art
The present invention relates to a local oscillation circuit which is usable as a tuner circuit in a television receiver, a CATV converter or an indoor unit of satellite receiver.
2. Background of the Prior Art
Recently, with the spread of CATV, multi channel receiving in television tuners and hence, an up-down type tuner or CATV converter is necessary. In one system, an input signal is converted to an intermediate frequency signal of higher frequency than the received signal and the intermediate frequency signal is then converted to a second intermediate frequency signal after passing through a narrow width band-pass filter (for example, published unexamined patent application SHO No. 59-149405). A feature of the system is that multi-channel receiving is achieved using simple structure by varying an oscillation frequency of a local oscillator in a range of over 1 GHz. The local oscillation circuit disclosed in published unexamined patent application SHO No. 59-149405 will now be described with reference to the Figures.
In FIG. 1, the local oscillation circuit is comprised of an oscillation amplifier 1, a resonance circuit 2, and can vary its oscillation frequency by an external tuning DC voltage impressed on a terminal 1A. The oscillation output signal is amplified in an amplifier 3 and fed to an external load circuit through an output terminal IB. The amplifier 3 operates as a buffer for the external load circuit and improves the local oscillation circuit.
FIG. 2 shows a circuit diagram of FIG. 1. Blocks encircled by broken lines correspond to blocks in FIG. 1. The amplifier 1 for oscillation is provided in a manner that the collector of an oscillation transistor Q.sub.1 is grounded with regard to alternating current through a by-pass capacitor to make a negative impedance seen from the base of the oscillation transistor Q.sub.1. Bias resistor R.sub.1 is connected between the collector and base of oscillation transistor Q.sub.1. The base of the oscillation transistor Q.sub.1 is connected through a coupling capacitor C.sub.2. A series resonant circuit is formed by a variable capacitance diode D.sub.1, a resonant inductance L.sub.1, and the internal capacitance of the transistor Q.sub.1. By grounding the other end of the series resonant circuit with regard to alternating current, negative gain seen from the base of transistor Q.sub.1 and loss of resonant inductance L.sub.1 are offset, and it oscillates with such a frequency that the phase characteristics seen from the base of transistor Q.sub.1 become 2n.pi.(n=0,1,2,3 . . . )rad.
By varying a tuning D.C. voltage impressed on a terminal 1A, the capacitance of the variable capacitance diode D.sub.1 varies, and amplitude and phase characteristics vary. The tuning voltage passes through bias resistor R.sub.4. By-pass capacitor C.sub.6 is grounded from the terminal 1A. The oscillation output signal is obtained at a common connection point between the emitter of transistor Q.sub.1 and a choke coil L.sub.2 by grounding the emitter of transistor Q.sub.1 with regard to direct current through a resistor R.sub.3 with connected in series choke coil L.sub.2 to the emitter of transistor Q.sub.1. The oscillation output signal is fed to the base of an amplifier transistor Q.sub.2 through a coupling capacitor C.sub.3. A potential is applied to the base of transistor Q.sub.2 from a source voltage Vcc impressed on a terminal 1D through a choke coil L.sub.3 and resistor R.sub.6. The emitter of amplifier transistor Q.sub.2 is grounded and the collector of transistor Q.sub.2 is connected to the terminal 1D through the choke coil L.sub.3. The amplified oscillation output signal is fed to the exterior load from the collector of transistor Q.sub.2 through a coupling capacitor C.sub.5 and an output terminal 1B.
Two problems exist in the prior art of FIGS. 1 and 2. The first one is that when the tuning potential impressed on the terminal 1A is varied, a current flowing in the oscillation transistor Q.sub.1 varies a great amount with c

REFERENCES:
patent: 3813615 (1974-05-01), Okazaki
patent: 4494081 (1985-01-01), Lea et al.
patent: 4536724 (1985-08-01), Hasegawa et al.
Draper, D.: Recent developments in solid state sources for microwave instrumentation, in: Electronic Engineering, Jan. 1974, pp. 54-56, 58.

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