Cascaded Integrator Comb Filter

1. 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

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

3. 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.

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

5. CIC filter transfer function

6. CIC filter transfer function • 1 &2 stage CIC frequency response for M=8

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

8. CIC Implement of an Decimation Filter

9. CIC Implement of an interpolation Filter

10. Register Growth

11. 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

12. 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”

13. End • Thank you for your attention