Analog-to-digital converters

Claim 1

A bipolar analog-to-digital converter comprising a comparator having first and second inputs and an output, first and second switches for alternately connecting first and second signal levels to said first input, said first level comprising an input signal to be converted and said second signal level comprising a reference level, a storage device connected between said second input and said reference level, current generator means for delivering either a positive or negative current to said second input, depending upon input signal polarity, during a counting period while said first switch is connecting said first level to said first input to charge the storage device until a change of state occurs at the output of the comparator, selector means for determining the polarity of the current from said generator means depending upon the state of the output from the comparator, a counting pulse generator, counter means for determining the number of counting pulses emitted from the pulse generator during said counting period in which the current generator means is applied to the comparator before said change of state occurs; and a clocking generator operative to generate control signals controlling periods of operation of said converter and including generator means operative for generating a stop signal each time the comparator changes state, said periods including a first period during which said control signals actuate said switches to apply said first input level to said first input of said comparator while the comparator settles, a second counting period initiated by said clocking generator during which said control signals initiate delivery of pulses to said counter means and actuate said current generator means to apply current of selected polarity to said storage device and to said second input of the comparator until its output changes state, a third period initiated by the latter change of state during which said control signals disable said current generator means reverse said switches to substitute said second reference level for said first input level and cease the delivery of pulses to said counter means, and a fourth period initiated by said clocking generator during which said control signals actuate current generator means to apply a current of reversed polarity to said storage device and to said second input to the comparator until its output again changes state and actuates the generator means to deliver a stop signal for initiating a succeeding first period.