Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
2001-03-29
2001-12-04
Pascal, Robert (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C330S20700P, C330S297000, C381S094500
Reexamination Certificate
active
06326844
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to amplifiers having provisions for reducing recovery time for transient operating conditions and particularly to transient suppression circuitry for reducing the effect of transients which may accompany the input signal to an amplifier.
BACKGROUND INFORMATION
Various methods are known for protecting an audio amplifier from transient effects. As an example, Morris , Jr. et al. in U.S. Pat. No. 5,224,169 describes a system including stereo amplifiers, each supplied with dual supply voltages (+V and −V). A detector, coupled to the amplifier outputs, senses the amplifier output voltage and turns off the positive and negative supplies if sustained DC is present or if either supply fails. Brief DC transients (i.e., not “sustained”) which may accompany the input signal may not be sensed. Lendaro, in U.S. Pat. No. 5,157,353 describes a protection circuit wherein the dual power supplies of an operational amplifier are provided with “slow start” circuitry which limits the rate of change of the supply voltages to suppress turn-on/turn-off transients. There is no provision, however, for suppressing transients which may accompany the input signal.
Other examples of amplifier protection circuits are described, for example, by Griffis in U.S. Pat. No. 4,405,948 in which supply voltage transients are detected and used for reducing the gain of a variable gain amplifier preceding an audio amplifier. In U.S. Pat. No. 5,199,079 Anderson et al. describe an arrangement including an amplifier having bias and supply voltages obtained from diode isolated filters that reduce the voltages slowly when the main voltage supply is de-energized.
SUMMARY
The present invention resides, in part, in the discovery of a heretofore unrecognized problem regarding transient effects which may occur in certain types of amplifiers. Specifically, in certain amplifier applications there may be only a uni-polar power supply available for operation of an amplifier normally requiring a bi-polar supply (as described in detail later). It has been found, in accordance with an aspect of the invention, that in such applications an input signal transient may result in a condition wherein the voltages of power supply filter capacitors may be disturbed by transients accompanying the amplifier input signal and this disturbance may degrade the amplifier transient response.
It is an object of the invention, to reduce the effect of input signal transients on the supply voltages of an amplifier.
Amplifier apparatus embodying the invention comprises a filter including first and second capacitors coupled in series across the outputs of a DC supply. Output voltages developed across the capacitors are applied to respective supply terminals of an amplifier which has an output coupled to a common connection of the two capacitors via a load. A feedback circuit is provided for suppressing transients at an input of the amplifier in response to an unbalanced condition of the output voltages of the filter.
In an exemplary application of the principles of the invention, the feedback circuit comprises a bias supply having an output providing a bias voltage indicative of a difference in the capacitor voltages and a threshold device coupled between the output of said bias supply and the input of the amplifier.
REFERENCES:
patent: 3947636 (1976-03-01), Edgar
patent: 4405948 (1983-09-01), Griffis
patent: 5157353 (1992-10-01), Lendaro
patent: 5199079 (1993-03-01), Anderson et al.
patent: 5224169 (1993-06-01), Morris, Jr. et al.
patent: 5751822 (1998-05-01), Yamaguchi et al.
patent: 5796850 (1998-08-01), Shiono et al.
patent: 6172561 (2001-01-01), Schott
Herbert Sax “HIFI IM Fernsehgerat Anspruch Oder Wirklichkeit” Funkschau, No. 25/26, 1981 pgs. 65-67.
R.W.J. Barker et al “Gate-Circuit Protection Safeguards MOSFET Amplifier” Electronic Engineering, vol. 44, No. 527, Jan. 1972 pgs 31-32.
“Power Amplifier (Buffer) with Low Output Impedance and Current Measurement Capability” IBM Technical Disclosure Bulletin, vol. 30, No. 7, Dec. 1987, pp. 95-97.
Hoover Alan Anderson
Morris, Jr. Robert Edward
Akiyama Kuniyuki
Choe Henry
Pascal Robert
Thomson Licensing SA
Tripoli Joseph S.
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