National Semiconductor Corporation

William H Gross

Tadashi Sakurai

An operational power amplifier having a bootstrap power output stage is designed to provide maximum dynamic range over a wide range of supply voltages. A control circuit in the form of a switched current mirror is added to the amplifier biasing circuit. At supply voltage higher than a predetermined threshold, the amplifier bias is adjusted to provide one half of this voltage at the output terminal. For supply voltages less than the threshold value, the output voltage is made less than half supply voltage.

Low voltage op amp bias optimizer

In an integrated circuit audio power amplifier a 6 db per octave frequency-gain roll off is obtained in a conventional manner by converting a high gain inverter to an integrator and driving the integrator from a current source. A second cascaded stage is also provided so that it operates at lower gain and has a matching high frequency roll off. When such characteristics are combined in cascade the result is a 12 db per octave roll off at the higher frequencies. A flat negative feedback loop is employed to maintain a controlled constant low frequency gain. In the response region located between the 12 db per octave slope region and the constant gain region there is a 6 db per octave slope. The configuration is stable without resorting to frequency sensitive feedback. When such an amplifier is constructed to have its gain versus frequency roll off to unity at the low frequency end of the AM radio broadcast band, the amplifier will emit very little energy in the radio band, yet a sufficient audio bandwidth is available for Hi Fi response.

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Tokyo, Japan

William H Gross