Improving Wideband Multichannel Systems with IC Integration (Part 2) (.PDF Download)
While phase-offset blocks located at numerically-controlled-oscillator (NCO) outputs can serve to create phase alignment at a single frequency, subarray calibrations often require phase alignment throughout the full frequency band of interest. In addition, we want to achieve amplitude equalization, in which all channels have nominally identical amplitudes with respect to a common reference channel, and amplitude gain flattening, in which all channels possess a nonchanging amplitude response with respect to frequency.
To obtain broadband phase and amplitude correction, it’s often necessary to use another DSP block: a finite-impulse-response (FIR) filter.1 FIR filters are a type of digital filter that’s heavily used in DSP, and its coefficients dictate the amplitude and phase response of the input digital signal. Systems that enable these coefficients to be changed are considered programmable FIR (pFIR) filters. They allow users to generate their own desired magnitude and phase response for each channel.