Cascaded Integrator Comb Filter 長庚電機通訊組 碩一 張晉銓 指導教授 : 黃文傑博士

Outline What is Cascaded Integrator Comb (CIC) Filter CIC filter transfer function CIC filter Implemented Register Growth Conclusions

What is Cascaded Integrator Comb (CIC) Filter In SDR system, samples rate changes very large. A digital linear phase finite impulse (FIR) filters for decimation and interpolation. No multipliers and use limited storage. Cascaded ideal integrator stages operating at a high sampling rate and an equal number of comb stages operating at a low sampling rate.

What is Cascaded Integrator Comb (CIC) Filter Well-suited for FPGA and ASIC implementation Reduce the computational expense of the operation

CIC filter transfer function

1 &2 stage CIC frequency response for M=8

CIC filter transfer function 4 stage CIC frequency response for M=8 &16

CIC Implement of an Decimation Filter

CIC Implement of an interpolation Filter

Register Growth

Conclusions Advantage No multipliers,no storage is required for filter coefficients The structure of CIC filters is very “regular” Little external control or complicated local timing is required Easily design for wide range of rate change factors “M”, with addition of scaling circuit and minimal changes filter timing

Conclusions Disadvantage Register widths can become large with “M” If system with a fixed decimation ratio, need a designed filter to compensate for the CIC passband droop. Frequency response is fully determined by M & L A new CIC decimation filter with using “sharpening”

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