Triple-slope analog-to-digital converters

Claim 1

An analog-to-digital converter comprising an integrating means having an input and an output, means for applying an analog input signal to be converted to the input of the integrating means to drive the integrating means output from a datum level to a level dependent upon the magnitude of the input signal, a source of a reference signal, means for applying the reference signal to the input of the integrating means to drive the integrating means output to the datum level and thereby generate a ramp function, a counter, means for generating clock pulses, means for causing clock pulses to be counted by the counter during an interval commencing with the application of the reference signal, means for applying a first increment to the ramp function before the ramp reaches the datum level a first time, means for detecting when the ramp reaches the datum level, means for applying to the ramp function a second increment equal in magnitude but opposite in polarity to said first increment, and means for scaling down the reference signal and the numerical weighting with which the clock pulses are counted by a common factor, the means for applying the second increment and the means for scaling down the reference signal and the numerical weighting of the clock pulses being responsive to operation of said detecting means when the ramp reaches the datum level said first time, and said detecting means being operative to determine the count in the counter when the ramp reaches the datum level a second time, whereby the count in the counter when the ramp reaches the datum level said second time provides a digital representation of the analog signal magnitude.