Patent ID: 6326793
Filing Date: 2001-12-04
Classification: G01R

Abstract:
A method of automatically verifying the characteristic frequency response of a low-pass filter having inputs and outputs, comprising the steps of:(a) providing a low-pass filter to be tested, the filter having inputs;(b) applying an a.c. test signal over a predetermined range of frequencies to the inputs of the filter;(c) measuring for each of the frequencies a test voltage developed across the inputs of the filter;(d) obtaining estimates of open circuit voltage at one representative frequency or over the predetermined range of frequencies;(e) estimating a voltage ratio in dB of the test voltage to the open circuit voltage at each of the frequencies;(f) associating the voltage ratios in dB with the particular frequency of the test signal and ordering such associated data by frequency;(g) estimating the frequency at which the voltage ratio is 3 dB less than the estimated voltage ratio at the lowest frequency;(h) comparing the associated data at the 3 dB frequency with the next highest frequency data to determine whether the voltage ratio has decreased by an amount equivalent to less than 20 dB per decade;(i) repeating step (h) with successive sets of associated data until the voltage ratio has decreased by an amount equivalent to less than 20 dB per decade;(j) continuing to step through the associated data until the ratio increases by an amount equivalent to less than 20 dB per decade;(k) differencing the associated data and subtracting a mean value to form a set of differenced data;(l) stepping through the differenced data and noting the first negative value and next subsequent positive value as turning points of the frequency response.