Digital filters for remote control receivers
First Claim
1. A digital filter for remote control receivers which operates in response to control signals at a predetermined input frequency superimposed on a power supply voltage, comprising first and second digital filter stages of the second order connected in cascade, each of said first and second digital filter stages including means for positioning the zeros in the pass-band of the filter stage so as to reduce the resonant frequency amplification of the filter wherein the filter coefficients of each filter stage are such that the zeros in the pass-band of the filter are positioned in terms of frequency, between + and -50% of the resonant frequency (fg) adjacent thereto by placing conjugate complex zeros on the circle of unit radius of the z-plane.
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Abstract
In providing digital filters for remote control receivers, in particular, for audio-frequency centralized ripple control receivers in an economic manner, it is advantageous to be able to use a processor unit with as low a bit number as possible (for example, an 8-bit microcomputer). In a conventional design of a filter according to the prior art, the dynamic range which is provided with an 8-bit processor element is insufficient in ensuring a perfect operation of the filter when a quality factor Q of about 30 is needed for the intended purpose of use and, on the other hand, when the dynamic range of the wanted signal which is given in practice is taken into consideration. A solution is indicated which overcomes these difficulties, which particularly involves the selected arrangement of zeros in the pass-band of the filter.
13 Citations
5 Claims
- 1. A digital filter for remote control receivers which operates in response to control signals at a predetermined input frequency superimposed on a power supply voltage, comprising first and second digital filter stages of the second order connected in cascade, each of said first and second digital filter stages including means for positioning the zeros in the pass-band of the filter stage so as to reduce the resonant frequency amplification of the filter wherein the filter coefficients of each filter stage are such that the zeros in the pass-band of the filter are positioned in terms of frequency, between + and -50% of the resonant frequency (fg) adjacent thereto by placing conjugate complex zeros on the circle of unit radius of the z-plane.
Specification