Design and economical realisation of a hybrid RC-active lowpass filter for PCM

The design of an economical hybrid RC-active lowpass filter for bandlimiting a PCM channel is described. An initial design is based on simulating an LC ladder filter with complex terminations; however, manufactured samples fail the specification because of parasitic effects, particularly stray capacitances which are large for the low-cost method of construction adopted. These effects are compensated in a second design based on an RLC ladder filter with finite Q-factor resonant circuits. Manufactured samples meet the specification and a Monte Carlo analysis predicts a high yield.