Analog to digital converter having no zero or span drift

Details Analog to digital converter having no zero or span drift Analog to digital converter having no zero or span drift

1987-06-15

1988-08-16

Shoop, Jr., William M.

Communications: electrical

Audible indication

Percussion-type sound producer

328127, 340347AD, H03M 106

Patent

active

047647523

ABSTRACT:
This invention relates to an analog to digital convertor in which zero drift and span drift are eliminated. The first differential amplifier has inputs of an analog voltage which can be switched between its positive input terminals in polarity and a reference voltage which can be switched between its negative input terminals. The output of the summing amplifier is integrated in a positive differential integrator, preferably, and fed through a crossover detector to detect crossover of the signals from the two sides of the integrator. Integration is carried out while adding the reference voltage and the analog voltage over a first fixed time period. The reference voltage is then reversed over a second time period to perform a first conversion. The start and stop signals of these time periods are used to start and stop a pulse counter. A second conversion is carried out by subtracting the analog voltage from the reference voltage and then reversing the reference voltage after said fixed time period until crossover occurs, defining third and fourth periods over which the counter counts the pulses. These define the counts N.sub.0, N.sub.2, N.sub.0 and N.sub.4. N.sub.2 - N.sub.0 is then divided by N.sub.2 +N.sub.0 to obtain a signal proportional to the analog voltage having no span drift. N.sub.0 -N.sub.4 can then be divided by N.sub.0 +N.sub.4 to obtain a signal proportional the analog voltage having no span drift. These two signals can be added together to obtain a signal proportional to the analog voltage having no span or zero drift.

REFERENCES:
patent: 4361811 (1982-11-01), Ormond

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