LogiCORE CIC Filter v1.0 and v3.0 - The CIC filter exhibits overflow for maximum inputs

AR#	12480	Search For Another Answer
Topic	IP-DSP Horizontal
Last Updated	09/15/2008
Status	Active

Description

Keywords: Core, CORE Generator, CORE Generator, SysGen, 2.2, 2.3, 3.1, 6.1, 6.1.1, 6.2, 7.1, 8.1, CIC, overflow

Why does my CIC v3.0 filter exhibit overflow for inputs that use the complete dynamic bit range of the data input?

Solution

The overflow occurs because the output is one bit too small. A simple way to work around this problem is to not use the full dynamic range of your input. For example, if you input a 12-bit sine wave to the filter, create a 13-bit input, but use a 12-bit sine wave.

The problem occurs because of an error in the size of the output bit width of the CIC. If you are using System Generator for DSP, you can use the CIC filter available in the reference designs. This CIC is also smaller than the core.

NOTE: The core should be full-precision when used in System Generator for DSP, so this situation should not occur; however, this might occur for every parameterized core that is generated.