Adaptive bias circuit for preventing turnoff in a push-pull stag

Details Adaptive bias circuit for preventing turnoff in a push-pull stag Adaptive bias circuit for preventing turnoff in a push-pull stag

1990-06-26

1991-05-28

Mottola, Steven

Amplifiers

With semiconductor amplifying device

Including push-pull amplifier

330274, H03F 326

Patent

active

050197894

ABSTRACT:
A push-pull amplifier circuit includes an NPN pullup transistor and an pulldown transistor, an emitter of the pullup transistor being coupled to a collector of the pulldown transistor. A first resistor is coupled between an output conductor and the emitter of the pullup transistor, and a second resistor is coupled between an emitter of the pulldown transistor and a supply voltage. A bias circuit includes a phase splitting transistor having an emitter coupled to a constant bias current source and a base of the pullup transistor, a collector coupled to a base of the pulldown transistor, and a control electrode coupled to an input signal. The phase splitting transistor steers a portion of the bias current into a first conductor connected to the base of the pullup transistor and a portion of the bias current into a second conductor connected to the base of the pulldown transistor in response to an input signal applied to the control electrode of the phase splitting transistor. A change in an output current flowing through the output conductor changes a base-emitter voltage of the pullup transistor by flowing through the first resistor and changing the voltage across the first resistor to compensate for steering current from the constant bias current source out of the first conductor to maintain a minimum amount of bias current flowing in the pullup transistor when the pulldown transistor is turned on hard, thereby reducing crossover distortion, maintaining output impedance low, and increasing bandwidth of the circuit.

REFERENCES:
patent: 3379986 (1986-04-01), Leslie
patent: 3995228 (1976-11-01), Pass
patent: 4274059 (1981-06-01), Okabe
patent: 4401951 (1983-08-01), Tanaka
patent: 4573021 (1986-02-01), Widlar
patent: 4922208 (1990-05-01), Susak et al.

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