National Semiconductor Corporation

Sai L Ting

Parviz Ghaffaripour

Arthur Joseph Kalb

Nick M Johnson

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.

Amplifier circuit with reduced DC power related transients

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. Hence, turn-on and turn-off transients in the output signal due to circuit turn-on and turn-off are avoided.

Amplifier circuit with reduced turn-on and turn-off transients

A driver which is particularly suitable for use with a backplane transceiver logic bus in a computer system is disclosed. In a preferred embodiment, a MOSFET is connected such that its gate and source are in a feedback loop which includes an amplifier and a first switching MOSFET. The source and drain of the MOSFET are connected in a connection path from the bus to ground, and a second switching MOSFET is connected between the gate of the MOSFET and ground. The first and second switching MOSFETS are arranged such that they switch in opposition to each other (one being turned on when the other is turned off) and a CMOS input signal is connected to the gates of the switching MOSFETS. In one state of the driver the MOSFET is turned off, in the other state the feedback loop is closed and the MOSFET is conductive. The rise and fall times of the driver's output can be controlled independently of each other.

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San Jose, CA, United States of America

Sai L Ting