Method for designing an analog Nyquist filter

摘要

Methodologies for designing and assembling an analog Nyquist filter require a filter unit which includes a low pass filter in cascade with at least one tapped delay filter. A Signal Generator is used to generate a test pattern for input into the filter unit in order to create a reaction signal from the filter unit. This reaction signal is then compared with a desired Nyquist response. Based on this comparison, amplifier gains for taps in the tapped delay filter are weighted to establish a transfer function in the filter unit. In operation the transfer function shapes analog input signals with the desired Nyquist response for use as an output from the Nyquist filter.

主权项

1. A method for designing a Nyquist filter which comprises the steps of:
generating a test pattern, wherein the test pattern is an analog signal having a predetermined symbol rate (Rs); providing a filter unit, wherein the filter unit includes a low pass filter and a tapped delay filter, wherein the tapped delay filter has an N number of taps, wherein N is an integer greater than zero, and wherein each tap individually samples the test pattern in compliance with the predetermined symbol rate, and wherein each tap has a dedicated amplifier; inputting the test pattern into the filter unit to create a reaction signal therefrom; sampling the test pattern an n number of times during each symbol cycle, wherein n is a real number greater than one (n>1), and N is greater than n (N>n); evaluating the reaction signal in comparison with a desired Nyquist response; and varying a gain for each dedicated amplifier in the tapped delay filter to weight samples taken by the respective tap, wherein the gain for each tap is based on the comparison made in the evaluating step and is used to alter the tapped delay filter to establish a transfer function, RC(α,f), in the filter unit, wherein α is a bandwidth factor and f is a frequency, for transforming the test pattern into a reaction signal corresponding to a desired, sin c-corrected Nyquist output response, for subsequent use of the filter unit as the Nyquist filter.