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Feedback-compensated ramp-type analog to digital converter

  • US 4,257,034 A
  • Filed: 02/27/1978
  • Issued: 03/17/1981
  • Est. Priority Date: 02/27/1978
  • Status: Expired due to Term
First Claim
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1. A feedback-corrected ramp-type analog-to-digital converter comprising:

  • means for generating a charging current;

    a ramp capacitor means responsive to said charging current for accumulating a charge thereon and generating a ramp voltage;

    first comparator means responsive to said generated ramp voltage and an analog input signal for outputting a pulse-width comparator output as long as the value of said analog input signal is greater than the value of said generated ramp voltage;

    first counter means operatively coupled to the output of said first comparator means and responsive to said pulse-width comparator output signal for counting clock pulses at a predetermined rate during the time duration of said pulse-width output signal so as to accumulate a digital number indicative of the value of said converted analog input signal when said pulse-width comparator output signal ends;

    second counter means for storing a zero count when said ramp capacitor means is discharged prior to the initiation of a particular conversion and for counting clock pulses during the generation of said ramp voltage;

    decoding means operatively coupled to the outputs of said second counter means for pre-assigning a particular desired level of ramp voltage with a predetermined count number attained by said second counter means and for generating a "count detection" signal in response thereto;

    voltage level comparator means for detecting when said generated ramp voltage reaches said particular desired level of ramp voltage assigned to said predetermined count number and generating a "voltage equal" signal in response thereto;

    logic means for detecting the time difference between the time of generation of said "count detection" signal and said "voltage equal" signal as a measure of ramp rate error and for generating a signal indicative of ramp rate error in response thereto; and

    means operatively coupled to said charging current-generating means and responsive to said signal indicative of ramp rate error for selectively increasing or decreasing the supplying of said charging current to said ramp-generating capacitor means to form a closed control loop for automatically correcting the rate of generation of said ramp voltage.

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