Amplifiers – With semiconductor amplifying device – Including frequency-responsive means in the signal...
Patent
1998-09-03
2000-07-11
Mottola, Steven J.
Amplifiers
With semiconductor amplifying device
Including frequency-responsive means in the signal...
330137, H03F 3191, H03G 318
Patent
active
060879017
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a tuning amplifier permitting only a pass of predetermined frequency components.
BACKGROUND ART
For use as a tuning circuit, various configurations using active elements and reactance elements have hitherto been proposed and put to practical use.
A conventional tuning circuit utilizing an LC resonance for example has a gain depending on an LC circuit, which gain may vary upon the regulation of a tuning frequency. Furthermore, typical tuning circuits extract predetermined frequency components from input signals, so that there may usually occur an attenuation of a signal amplitude with the gain resulting in 1 or less at the tuning frequency. For this reason, if amplification is required, a separate amplifier circuit must be connected thereto for amplifying the signal amplitude.
DISCLOSURE OF THE INVENTION
The present invention was conceived in order to solve such a problem. It is therefore the object of the present invention to provide a tuning amplifier ensuring a stabilized output amplitude and capable of amplifying a signal amplitude simultaneously with tuning.
A tuning amplifier in accordance with the present invention comprises an oscillation circuit for performing an oscillating action at a predetermined frequency, the oscillation circuit allowing its output to be fed back to its input side to form a closed loop; a gain control circuit for providing a control of an output amplitude of the oscillation circuit; and an input circuit for feeding signals to a part of the closed loop of the oscillation circuit. In case the oscillation circuit in its oscillation mode receives a signal having a frequency in the vicinity of the oscillation frequency, a phenomenon has been confirmed that the oscillation output is drawn into the frequency of the input signal, allowing a predetermined tuning action. Due to a regulation of the output amplitude effected by a gain control circuit in particular, there occurs no variation in gain even when the tuning frequency has been altered by varying the oscillation frequency of the oscillation circuit. A regulation of the response speed of the gain control circuit enables the oscillating action to be performed in response to various input AC signals such as an AM modulated signal and an FM modulated signal. It has also been confirmed that the above oscillating action is actually achieved when the output amplitude of the oscillation circuit is set to a value fairly smaller than that of the power source voltage, with the amplitude of the input AC signal being set to a value fairly smaller than this oscillation amplitude. If the input AC signal amplitude is taken as a criterion, a gain of several tens of decibels is achieved, allowing the amplification of the signal amplitude simultaneously with the oscillating action.
The tuning amplifier of the present invention employs a PLL configuration including the oscillation circuit in the form of a voltage controlled oscillation circuit, enabling the stability of the tuning frequency to be easily achieved. In particular, the above oscillation circuit performs a predetermined oscillating action in case of no input signals so that a PLL control can be provided irrespective of the presence of the input signals.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing a configuration of an embodiment of a tuning amplifier;
FIG. 2 is a diagram showing a configuration to PLL control the tuning amplifier in FIG. 1;
FIG. 3 is a circuit diagram showing a first configuration example of the tuning amplifier using the phase-shift type oscillation circuit;
FIG. 4 is a diagram showing the result of measurement of a tuning characteristic of the tuning amplifier in FIG. 3;
FIG. 5 is a diagram showing a tuning characteristic obtained when the input circuit has been connected to connection point A of FIG. 3;
FIG. 6 is a diagram showing a tuning characteristic obtained when the input circuit has been connected to the connection point B of FIG. 3;
FIG. 7 is a diagram showing a manner of variation
REFERENCES:
patent: 5886580 (1999-03-01), Ikeda et al.
Nakanishi Tsutomu
Okamoto Akira
Mottola Steven J.
T.I.F. Co., Ltd
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