Burr-brown Corporation

Justin A McEldowney

William J Lillis

An offset-compensated amplifier including an input stage (2) having a current source (10), first (11) and second (12) FETs each having a source connected to the current source, first (17) and second (18) input FETs each having a source connected to a drain of the first compensation FET (11), and third (19) and fourth (20) input FETs each having a source connected to a drain of the second compensation FET (12), a drain of each of the first (17) and third (19) input FETs being connected by a first output conductor (21) to a first load (23), and a drain of each of the second (18) and fourth (20) input FETs being connected by a second output conductor (22) to a second load (24), a gate of each of the first (17) and third (19) input FETs being connected to a first input (3A), a gate of each of the second (18) and fourth (20) FETs being connected to a second input (3B). Auto-zeroing circuitry (3) including switching circuitry (32A, 32B) operative to short-circuit the first (3A) and second (3B) inputs to cause the input stage (2) to produce a gained-up offset voltage between the first (21) and second (22) output conductors, switched capacitor circuitry (26A, 26B, 27A, 27B) operative to store the gained-up offset voltage, and compensation circuitry (28) operative to apply compensation signals to the gates of the first (11) and second (12) compensation FETs in response to the stored gained-up offset voltage.

Offset-compensated amplifier input stage and method

An electronically controllable low capacitance active bus line terminator achieves low output terminal capacitances by connecting emitters of switch transistors directly to the output terminals. Termination resistors are connected directly between an output of a voltage regulator circuit and collectors of the switch transistors. Emitters of optional clamp transistors can be connected to bases or collectors of the switch transistors to limit or prevent 'ringing' of bus conductors connected to the output terminals if the switch transistors are turned on. The bus conductors are thereby isolated from parasitic capacitances associated with the termination resistors and the collectors of the switch transistors when they are turned off.

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Tucson, AZ, United States of America

Justin A McEldowney