Precision, low-power transimpedance circuit with differential current sense inputs and single ended voltage output

摘要

A transimpedance circuit adapted for use in a subscriber line interface circuit includes sense resistors installed in closed loop, negative feedback paths of respective sense amplifiers. Voltage drops across the sense resistors are applied to first and second differential coupling circuits for applying differential currents to complementary polarity inputs of an operational amplifier. The inputs of the amplifier are also coupled to a linearity compensator, that is configured to provide sufficient overhead voltages in the presence of worst case voltage swing conditions. The compensator has a differential amplifier configuration, that closes a negative feedback loop from the output of the amplifier and one of its inputs, relative to a reference voltage balancing path coupled to the amplifier's other (complementary) input. The balanced differential configuration forces corresponding terminals of a pair of load resistors coupled to the inputs of the operational amplifier to the same potential, irrespective of variations in the input currents.