Bias circuit for class AB high frequency amplifiers

摘要

A high-speed cascode amplifier includes a cascode input stage. The cascode input stage sinks a cascode current in proportion to an input signal. The cascode current is sourced through two conduction paths. A first conduction path corresponds to the operating current for a diode multiplier transistor. The second conduction path corresponds to an alternate conduction path other than through the diode multiplier transistor. The size of the diode multiplier transistor is reduced by proper arrangement of the alternate path, such that the frequency response of the amplifier is improved. The VCE of the diode multiplier transistor is maintained at a stable level by adjusting the bias current of the diode multiplier transistor. The diode multiplier provides a temperature-compensated bias current to the class AB amplifier stage for producing the output signal.