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CIC补偿滤波器

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Altera Corporation 1

AN-455-1.0 Preliminary

Application Note 455

Understanding CIC

Compensation Filters

Introduction

The cascaded integrator-comb (CIC) filter is a class of hardware-efficient

linear phase finite impulse response (FIR) digital filters. CIC filters

achieve sampling rate decrease (decimation) and sampling rate increase

(interpolation) without using multipliers. Altera’s CIC Compiler

MegaCore

®

function implements various CIC filters based on

Hogenauer’s method.

f CIC filters were first proposed by Eugene Hogenauer in 1981, For more

information about CIC filters, refer to Eugene B. Hogenauer, “An

economical class of digital filters for decimation and interpolation,” IEEE

Transactions on Acoustics, Speech and Signal Processing, pp. 155-162, April

1981.

A CIC filter consists of an equal number of stages of ideal integrator filters

and comb filters. Its frequency response may be tuned by selecting the

appropriate number of cascaded integrator and comb filter pairs. The

highly symmetric structure of a CIC filter allows efficient implementation

in hardware. However, the disadvantage of a CIC filter is that its pass

band is not flat, which is undesirable in many applications. Fortunately,

this problem can be alleviated by a compensation filter.

This application note presents theory and methods for designing CIC

compensating filters for sample rate conversion systems. The MATLAB

Signal Processing Toolbox is used to design the coefficients of the

compensating FIR filters. This application note also describes how to

choose parameters for designing a compensation filter and then

implements an example decimation system using the Altera

®

CIC

Compiler MegaCore function and the FIR Compiler MegaCore function.

The following topics are discussed in this document:

■ “Prerequisites” on page 2

■ “CIC Filter Structure” on page 2

■ “CIC Compensation Filter Design” on page 4

■ “Data Rate Down Conversion Example” on page 11

■ “Conclusion” on page 17

April 2007, ver. 1.0

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