| 摘要 |
A multifunction amplifier uses a finite transconductance amplifier to provide an amplifier with a high impedance input and a desired output impedance. A pair of appropriate polarity binary signals are summed to form a ternary signal which may be filtered by a filter circuit upon command. The ternary signal, filtered or unfiltered, is input to one input of a differential transconductance amplifier while a feedback signal via a feedback path from an output node of the finite transconductance amplifier is input to the other input. The outputs of the differential transconductance amplifier are equally amplified by a pair of output current gain amplifiers. A unity gain bias level shifter is provided between one of the differential outputs and one of the pair of output amplifiers. The output amplifiers combine the amplified output currents at the output node. The finite transconductance of the finite transconductance amplifier is determined by the emitter resistors of the differential transconductance and output amplifiers, and the desired output impedance is a function of a feedback resistor that forms the feedback path, an input resistor to the differential transconductance amplifier and the finite transconductance. A current switch connects a constant current source to the differential transconductance amplifier to provide current bias upon command, the desired output impedance appearing at the output node when the current source is conducting and an essentially infinite output impedance appearing at the output node when the current source is not conducting.
|
