LogiCORE_cic

LogiCORE_cic - Cascaded Integrator-Comb (CIC) Filter V3.0...

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March 14, 2002 1 Xilinx, Inc. 2100 Logic Drive San Jose, CA 95124 Phone: +1 408-559-7778 FAX: +1 408-559-7114 URL: www.xilinx.com/ipcenter Support: www.support.xilinx.com Features Drop-in module for Virtex™, Virtex™-E, Virtex™-II, Virtex-II Pro™, Spartan™-II, and Spartan™-IIE FPGAs 1- to 32-bit input data precision Supports decimation and interpolation rate changes between 8 and 16,383 Dual-channel (time-shared) support for decimator structures Number of CIC stages programmable between 1 and 8 Multiplierless filter architecture is ideal for systems requiring compact filters operating at high sample rates Uses relationally placed macro (RPM) mapping and placement technology, for maximum and predictable performance Incorporates Xilinx Smart-IP™ technology for utmost parameterization and optimum implementation To be used with version 4.2i or later of the Xilinx CORE Generator System General Description Cascaded integrator-comb (CIC), or Hogenauer filters, are multirate filters used for realizing large sample rate changes in digital systems. Both decimation and interpola- tion structures are supported by the Core. CIC filters are multiplierless structures, consisting of only adders, subtrac- tors and registers. They are typically employed in applica- tions that have a large excess sample rate. That is, the system sample rate is much larger than the bandwidth occupied by the signal. CIC filters are frequently used in digital down-converters (DDCs) and digital up-converters. Applications Channelization functions in a digital radio or MODEM Part of the digital up-conversion signal processing chain in a transmitter Any filter structure that is required to efficiently effect a largesamp leratechange Theory of Operation The following description of the CIC decimator and interpo- lator is based closely on that provided in Reference 1 in the References section later in this document. CIC Decimator Figure 1 shows the basic structure for a CIC decimation fil- ter. The integrator section consists of N ideal integrator stages operating at the high sampling rate fs. Each stage is implemented as a one-pole filter with a unity feedback coef- ficient. The transfer functions for a single integrator is Hz z I () = 1 1 1 (1) Figure 1: CIC Decimation Filter. The CIC decimator consists of a cascade of integrators followed by a resampling switch and a cascade of differentiators. The differential delay M in the differentiator chain may be defined by the user to be either 1 or 2. z - M + - z - M + - z - M + - z - M + - y ( n ) x ( n ) 1to8s tages Sample rate = fs Sample rate = fs/R fs/R fs Cascaded Integrator-Comb (CIC) Filter V3.0 March 14, 2002 Product Specification
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Cascaded Integrator-Comb (CIC) Filter V3.0 2 March 14, 2002 The comb section operates at the low sampling rate fs/ R where R is the integer rate change factor. This section con- sists of comb stages with a differential delay of M samples per stage. The differential delay is a filter design parameter used to control the filter’s frequency response.
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LogiCORE_cic - Cascaded Integrator-Comb (CIC) Filter V3.0...

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