Amplifiers – Signal feedback – Phase shift means in loop path
Patent
1997-06-23
2000-06-27
Mottola, Steven J.
Amplifiers
Signal feedback
Phase shift means in loop path
330305, H03F 3191
Patent
active
060811579
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a tuning circuit easily adapted to an integrated circuit and capable of selectively providing as an output any desired frequency component in an input signal.
BACKGROUND OF ART
Generally, tuning circuits for receiving a video signal in a television receiver and the like require to have a relatively wide frequency bandwidth and thus use, for example, staggered tuning amplifiers. The staggered tuning amplifiers are a combination of plural stages of single tuning circuits, each adapted to choose a narrow frequency bandwidth signal, to provide a wide frequency bandwidth and a given amplification factor as a whole. Such amplifiers find wide applications not only in the above mentioned television receivers but also in intermediate frequency amplifiers for radar systems, etc.
A plurality of single tuning amplifiers constituting the above mentioned conventional staggered tuning amplifiers comprise a combination of resonance circuits, each including typically an inductor and a capacitor. By shifting the resonance frequencies by a given frequency from one another, a relatively flat, wide frequency bandwidth tuning characteristic may be obtained as a whole. Tuning frequencies in such staggered tuning amplifiers are determined by inductors and capacitors to be used as pairs. However, any attempt to obtain a wide frequency bandwidth by combining, for example, two stages of single tuning amplifiers with a certain frequency difference may result in a non-flat tuning characteristic with undesirable attenuation in the intermediate or center frequency range. This leads to a conclusion that the number of cascade connected, single tuning amplifier stages must be increased for wider frequency characteristic. In varying tuning frequencies of three or more stages of tuning amplifiers, the resonance frequency of each single tuning amplifier must be controlled in harmony with those in the other amplifiers, thereby making the control very complicated and subjecting to substantial change in characteristic when the tuning frequencies are varied. This is believed to be the reason why the tuning frequencies have never been varied in practical use. In a heterodyne system, for example, signal is processed after being converted into an intermediate frequency and thus the tuning frequency is maintained constant.
DISCLOSURE OF INVENTION
It is the object of the present invention to solve the above problems and to provide a tuning circuit having a wider tuning frequency bandwidth, capable of easily varying the tuning frequency bandwidth or the tuning frequency, and suitable to adapt to an integrated circuit.
The tuning circuit in accordance with the present invention comprises a plurality of cascade connected tuning amplifier sections, each having a substantially equal tuning frequency. Each of the tuning amplifier sections comprises an adding circuit for adding an input signal applied to one end of an input impedance element and a feedback signal applied to one end of a feedback impedance element, two phase shifting circuits of opposite phase shift directions to each other and including a series circuit of a first resistor and a capacitor or an inductor and a differential input amplifier, and a first voltage dividing circuit for dividing an input AC signal by a predetermined dividing ratio. The two phase shifting circuits and the first voltage dividing circuit are connected in a cascade manner. The added signal from the adding circuit is applied to the front stage circuit of the cascade connected circuits and the signal from the final stage is applied to one end of the feedback impedance element as the feedback signal. An output signal is derived from a circuit point before being divided by the voltage dividing circuit.
Also, the tuning circuit according to the present invention comprises a plurality of cascade connected tuning amplifier sections having sequentially different tuning frequencies by a given frequency. Each of the tuning amplifier sections comprises an adding circuit for a
REFERENCES:
patent: 3969682 (1976-07-01), Rossum
patent: 4246542 (1981-01-01), Thanos
patent: 4663597 (1987-05-01), Benzinger et al.
Ikeda Takeshi
Nakanishi Tsutomu
Ohe Tadataka
Ikeda Takeshi
Mottola Steven J.
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