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Decreased Distortion in Digital Filters

IP.com Disclosure Number: IPCOM000076511D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Pricer, WD: AUTHOR

Abstract

This output circuit for digital filters provides a decreased level of distortion in the reconstituted waveform. Most digital filter output circuits reconstitute the processed waveform with s stairstep approximation of the sample pulses. The following circuit reconstitutes the waveform by interconnecting the sample pulses with ramps.

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Decreased Distortion in Digital Filters

This output circuit for digital filters provides a decreased level of distortion in the reconstituted waveform. Most digital filter output circuits reconstitute the processed waveform with s stairstep approximation of the sample pulses. The following circuit reconstitutes the waveform by interconnecting the sample pulses with ramps.

The filter comprises an amplifier 10 having a fixed gain and a simple RC integrator 11 coupled thereto. The integrator may, of course, be incorporated in the amplifier. The time constant of the integrator is set so that in the time interval between samples, the voltage on the capacitor attains 1 (A + 1) fraction of the value it is approaching in that interval. Gains as low as ten achieve good results. As the gain of the amplifier is increased, the gain of the network approaches unity. Small errors in gain or time constant cause only small errors in the response.

The input sample is fed through sampling switch 12 onto holding capacitor
13. There it is compared with the sampled output of the integrator as sampled by sampling switch 14 and held by holding capacitor 15. From this comparison amplifier 10 determines the direction and slope of the succeeding ramp. When properly balanced within normal component tolerances, this circuit exhibits negligible drift in the bass line and accurately intersects all sample points regardless of direction or amplitude of excursion from the previous point.

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