18.2.2 Cascaded Integrator Comb (CIC) Filter

A cascaded integrator-comb (CIC) filter is a low-pass filter that can be used for anti-aliasing an analog signal from an ADC by oversampling the input and low-pass filtering to remove high-frequency components. It consists of a series of M accumulators operating at the input frequency, followed by a series of M differencers operating at an output frequency, which is equal to the input frequency divided by a decimation ratio R. The CIC filter of the dsPIC33AK256MPS306 family supports M = 2 and M = 1. Figure 18-5 shows the second-order CIC filter implementation. Figure 18-6 shows the magnitude spectrum of the CIC filter.

Although the CIC filter in the dsPIC33AK256MPS306 is designed to operate in conjunction with the resolver-to-digital conversion process, it can also be used independently when configured in register operating mode, allowing it to perform integration and decimation of digital samples.