Oscillators – Solid state active element oscillator – Transistors
Patent
1980-06-03
1984-02-07
Grimm, Siegfried H.
Oscillators
Solid state active element oscillator
Transistors
331140, 331183, H03B 526
Patent
active
044306270
DESCRIPTION:
BRIEF SUMMARY
RELEVANT ART
This invention relates to an amplitude control circuit for stabilizing the output signal amplitude of a sine-wave signal oscillator.
BACKGROUND OF THE INVENTION
For a sine-wave oscillator, especially an oscillator within a frequency range of a few Hz to a few hundreds KHz, Wien-bridge type or Sulzer type CR oscillator is generally used. Means for stabilizing the output signal amplitude often used are set forth as follows:
(a) By using a resistance variable element with Joule heat, such as a glass-tube enclosed type thermistor or a tungsten lamp.
(b) By using a resistance variable element with a control signal, such as an FET or a photo-cell type optical coupler.
The amplitude stabilizing means of the former (a) is popularly employed because of its simple construction. By means of (a), however, a low harmonics-distortion sine-wave signal below a few tens Hz is hardly obtained. Because the inner resistance of the amplitude stabilizing element is modulated by the amplitude change, not by the RMS (Root Mean Square) of the oscillation output signal amplitude. To solve this problem, an extremely large heat capacity is required for the amplitude stabilizing element. But a large heat capacity of the stabilizing element makes a trackability deteriorated, which the trackability means a response speed or a traceability for the average-variation of oscillation output amplitude. The deterioration of trackability will provide a fluctuation of the output amplitude, which is the so-called "hunting". The hunting phenomenon appears whenever the oscillation frequency is changed, and practically, this is very uncomfortable phenomenon. As mentioned above, matters to obtain a low harmonics-distortion and a little hunting at a low frequency range are contrary to each other.
The amplitude stabilizing means of the latter (b) is somewhat more complicated than the former (a) in consideration of the constructions or configurations. However, the amplitude stabilizing means of (b) is also often used. Because an amplitude stabilizing element for the (b) means is usually cheap device and hardly affected by surrounding temperature or mechanical vibration. In this means, the inner resistance of the amplitude stabilizing element is controlled by a control voltage or a control current. Suppose that we apply a source-drain resistance of FET to the amplitude stabilizing element. In this case the inner resistance of the FET is controlled by a gate-source voltage. Usually an average or peak level of rectified oscillation output signal is employed in the control voltage. Ripple components of the rectified oscillation output signal are eliminated through an eliminator or filter circuit.
In the case of the amplitude stabilizing means (b), when a low harmonics-distortion of oscillation output signal at low frequency range is required, a time constant of the filter circuit should also be set at large. Because an amplitude of ripple included in the control signal is enlarged with decrease of oscillation frequency, if the time constant is small. This ripple modulates the inner resistance of the amplitude stabilizing elements and makes the distortion factor of the oscillation output signal worsened. On the contrary a large time constant is applied to the filter circuit for lowering the distortion factor of oscillation output signal, said hunting phenomenon is in the forefront. Accordingly, even by the amplitude stabilizing means of (b), lowering the harmonics-distortion and avoiding the hunting phenomenon are the anti-requirement.
However, the art with the stabilizing means (b), which can solve the anti-requirement above-mentioned, i.e. provide a low harmonics-distortion and a little hunting, has been developed. To the best of inventor's knowledge, the most recent publication is "Transistor Technics" of October, 1978 published by CQ publishing company in Japan. In pages 283 to 300 of this publication a trial manufacture description of a sine-wave oscillator which may be solve said anti-requirement is disclosed. In the oscillator, a peak
REFERENCES:
patent: 2831975 (1958-04-01), Catherall
patent: 3851276 (1974-11-01), Kaplan
Burwen, "Ultra Low Distortion Oscillator" EDN/EEE, vol. 16, No. 11, Jun. 1, 1971, p. 45.
Grimm Siegfried H.
Westin Edward P.
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