Phase Response in Active Filters, Part 2: Low-Pass and High-Pass Responses

The transfer function of an active filter can be viewed as the cascaded response of the filter transfer function and an amplifier transfer function. This article examines the phase shift of the filter transfer function itself. While filters are designed primarily for their amplitude response, the phase response can be important in applications such as time delay simulation, cascaded filter stages, and especially process-control loops.

Difference Amplifier Forms Heart of Precision Current Source

Precision current sources are used to provide excitation for RTDs in process-control systems; to measure unknown elements in digital multimeters; and to drive 4 mA to 20 mA current loops, which are widely used to transmit information over long distances. This article shows how a difference amplifier can be used to implement a precision current source.