Parviz A Ghaffaripour

US Patent:

56487428, Jul 15, 1997

Filed:

Oct 23, 1995

Appl. No.:

8/546910

Inventors:

Parviz Ghaffaripour - Saratoga CA
Sai L. Ting - San Jose CA

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

H03F 114

US Classification:

330 51

Abstract:

An amplifier circuit with improved turn-on and turn-off transient operation includes an amplifier and a controller for controlling the mode of operation of the amplifier during initial and subsequent circuit turn-on and turn-off. The amplifier is biased by a positive power supply voltage and has a differential input which is driven by a reference voltage and a single-ended input signal. Where the output is single-ended, a single amplifier provides a single-ended output signal. Where the output is differential, the amplifier includes cascaded, differential input, single-ended output amplifiers which together provide a differential output signal. One of each of the differential inputs is driven by the reference voltage which, following circuit turn-on, charges to a value of half of the positive power supply voltage. Following circuit turn on and turn-off and during initial charging or discharging, respectively, of the reference voltage, the controller places the amplifier in an operation mode whereby the single-ended output signal follows the relatively slowly charging or discharging reference voltage and the differential output signal remains at zero. When the reference voltage is fully charged, the controller places the amplifier in another operation mode whereby both the single-ended and differential output signals become equal to the sum of the reference voltage and a multiple of the input signal.

US Patent:

57035296, Dec 30, 1997

Filed:

Mar 1, 1996

Appl. No.:

8/609726

Inventors:

Parviz Ghaffaripour - Saratoga CA
Arthur J. Kalb - San Jose CA
Nick M. Johnson - Los Altos CA
Sai L. Ting - San Jose CA

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

H03F 126

US Classification:

330 51

Abstract:

An amplifier circuit with improved turn-on transient operation includes a differential amplifier and a selectively variable reference generator for controlling the amplifier output during circuit turn-on. The amplifier is biased by a single power supply and its differential inputs are driven by a reference voltage from the reference generator and a single-ended input signal. Following circuit turn-on, the selectively variable reference voltage, generated by charging the bypass capacitor with a constant current source, charges in a linear manner from ground potential toward its final value of, typically, half of the power supply voltage. This allows improved turn-on transient operation to be realized, e. g. reduced "pops" and "clicks" upon circuit turn-on, while giving the user increased flexibility in selecting the sizes of the reference voltage bypass capacitor and the input signal coupling capacitor.

US Patent:

54365880, Jul 25, 1995

Filed:

Dec 17, 1993

Appl. No.:

8/168448

Inventors:

Parviz Ghaffaripour - Saratoga CA

Assignee:

National Semiconductor Corp. - Santa Clara CA

International Classification:

H03K 301

US Classification:

327538

Abstract:

A bias control circuit and an associated method in an audio output amplifier provide slow turn-on or turn-off operation of a bias voltage generation circuit, using an external bypass capacitor. A slow rate in the turn-on and turn-off operations in such a bias voltage generation circuit prevents click or pop noises. In one embodiment, two bipolar transistors each responsive to the voltage on an external capacitor are provided to gradually increase the voltage of an output node, which can be used to drive the gate terminal of an MOS transistor in the bias voltage generation circuit. Alternatively, in another embodiment, an MOS inverter, which receives as input the voltage on bypass capacitor, is provided to divert current from a conventional bias circuit. The rate at which the MOS inverter diverts current from the conventional bias circuit controls the slew rate in the turn-off operation of the bias current. Adjustment to this slew rate can be accomplished by adjusting the resistance and capacitance values of resistor and bypass capacitor, respectively.

US Patent:

56420749, Jun 24, 1997

Filed:

Oct 13, 1995

Appl. No.:

8/542596

Inventors:

Parviz Ghaffaripour - Saratoga CA
Nick M. Johnson - Los Altos CA

Assignee:

National Semiconductor Corporation - Santa Clara CA

International Classification:

H03F 126

US Classification:

330 51

Abstract:

An amplifier circuit with improved turn-on and turn-off transient operation includes an amplifier and a controller for controlling the amplifier output during initial and subsequent circuit turn-on and turn-off. The amplifier is biased by a positive power supply voltage and has a differential input driven by a reference voltage and a single-ended input signal. Where the output is single-ended, a single amplifier provides a single-ended output signal. Where the output is differential, the amplifier includes cascaded, differential input, single-ended output amplifiers which together provide a differential output signal. Following circuit turn-on and turn-off, the reference voltage, which drives one of each of the differential inputs, typically charges to or discharges from, respectively, a value of half of the positive power supply voltage. Following circuit turn-on and turn-off and during initial charging or discharging, respectively, of the reference voltage, the controller forces the single-ended output signal to follow the relatively slowly charging or discharging reference voltage and the differential output signal to remain at zero. When the reference voltage is fully charged, the controller releases control and both the single-ended and differential output signals become equal to the sum of the reference voltage and a multiple of the input signal.