Analog to digital converter with automatic calibration

Claim 2

MethOd for measuring an unknown input voltage comprising the steps of repeatedly generating a ramp which varies in voltage at a linear rate; providing first and second reference voltages; selectively comparing said ramp voltage to said first reference voltage, the unknown input voltage, and said second reference voltage during each repetition of said ramp; determining the time between the coincidence of the ramp voltage with said first reference voltage and with said second reference voltage to obtain a reference time interval; determining the time interval between the coincidence of said ramp voltage with the unknown input voltage and one of said reference voltages to obtain a measurement time interval; and determining the time ratio between said reference time interval and said measurement time interval; indicating the magnitude of the unknown input voltage by reference to said time ratio and the magnitudes of said reference voltages.

Claim 3

The method of claim 1 further including the steps of generating a predetermined number of pulses during said reference time interval; and gating a number of said pulses in proportion to said time ratio to a display device to indicate the magnitude of said unknown input voltage.

Claim 4

The method of claim 2 wherein the steps of generating a predetermined number of pulses during said reference time interval includes the steps of generating a series of regularly spaced pulses; counting the number of pulses generated during the reference time interval; and adjusting the frequency of said pulse generator so that said predetermined number of pulses occurs during said reference time interval.

Claim 5

The method of claim 3 including the steps of clamping said pulse generator into a nonoscillating state prior to said reference time interval and gating said pulse generating means into operation at the beginning of the reference time interval so that the phase of said pulse generating means at the beginning of said interval is the same for each measurement.

Claim 6

The method of claim 1 wherein said first and second reference voltages are of equal magnitude and of opposite polarity, and wherein the time of coincidence of the ramp voltage with the unknown input voltage is measured with respect to a time which is one-half of the reference time interval so that the magnitude of the unknown input voltage is directly proportional to the measured time interval.

Claim 7

The method of claim 5 wherein the polarity of the unknown input voltage is determined by whether the measured time interval starts or ends with the time which is one-half said reference time interval.

Claim 8

A drift free measuring circuit for measuring the magnitude of an unknown input signal comprising means for repeatedly providing a ramp signal which changes in magnitude at a linear rate; means for providing a first reference signal; means for providing a second reference signal; means for selectively comparing said ramp to said first reference signal, the input signal and said second reference signal during each repetition of said ramp signal; and means for measuring the time ratio between the comparison of said ramp signal to said first and said second reference signals and said ramp signal to said input signal and one of said reference signals to provide a measurement of the magnitude of the unknown input signal, the measurement of said input signal thereby being determined solely by reference to said first and second reference signals and independent of the slope of said ramp signal.

Claim 9

A drift free measuring circuit for measuring the magnitude of an unknown input signal comprising means for repeatedly providing a ramp signal which changes in magnitude at a linear rate; means for providing a first reference signal; means for providing a second reference signal; means for selectively comparing said ramp to said first reference signal, the input signal and said second reference signal during each repetition of said ramp signal; and means for measuring the time ratio between the comparison of said ramp signal to said first and said second reference signals and said ramp signal to said input signal and one of said reference signals to provide a measurement of the magnitude of the unknown input signal, the measurement of said input signal thereby being determined solely by reference to said first and second reference signals and independent of the slope of said ramp signal.

Claim 10

The device of claim 7 wherein said means for measuring the time ratio includes means for generating a series of regularly spaced pulses; counter means connected to said pulse generating means to divide the number of said pulses by a fixed number; means for initiating the counting sequence upon an output from said comparator means indicating the coincidence of said ramp signal and said first reference signal; means for comparing the output of said counter with the output of said comparator when indicating the coincidence of said ramp signal and said second reference signal; feedback means connected to said pulse generating means and responsive to said comparator means for maintaining the number of said pulses constant during the reference time interval between the coincidence of said ramp with said first reference signal and with said second reference signal.

Claim 11

The device of claim 8 wherein said pulse generating means is a voltage controlled oscillator and wherein said comparator means controls the frequency of said oscillator to maintain a fixed number of pulses within said reference time interval.

Claim 12

The device of claim 8 wherein said first and second reference signals are of equal magnitude and of opposite polarity.

Claim 13

The device of claim 8 further including means responsive to the coincidence of said ramp signal with said unknown input signal and to said counter means for gating the output of said pulse generating means to a digital readout counter with the number of pulses so gated being directly proportional to the magnitude of said unknown input signal with reference to zero.

Claim 14

A drift free voltage measuring circuit for indicating the magnitude and polarity of an unknown input comprising means for providing a ramp voltage which changes in magnitude at a linear rate between a positive and a negative value; means for providing first and second reference voltages having equal magnitudes and opposite polarities; means for selectively comparing said ramp voltage to said first reference voltage, the unknown input voltage, and said second reference voltage; means for generating regularly spaced pulses; counter means responsive to the output from said pulse generating means for counting the number of pulses generated in a reference time interval between the coincidence of said ramp voltage with said first and said second reference voltages; feedback means responsive to said counter means and said comparing means for controlling the frequency of said pulse generating means to maintain the number of said pulses in the reference time interval at a predetermined number; means for gating a portion of the output of said pulse generating means to a digital display device in response to the coincidence of said ramp voltage with said unknown input voltage and in response to an output from said counter means representing one-half of said predetermined number of pulses thereby to provide a number of pulses to the display device which is a direct function of the magnitude of the voltage of said unknown input with respect to zero; and means for determining the sequence of occurrence of the coincidence of the ramp voltage with said unknown input and the output from said counter representing one-half said predetermined number of pulses to provide an indication of the polarity of the unknown input.

Claim 15

A drift free voltage measuring circuit for indicating the magnitude and polarity of an unknown input comprising means for providing a ramp voltage which changes in magnitude at a linear rate between a positive and a negative value; means for providing first and second reference voltages having equal magnitudes and opposite polarities; means for selectively comparing said ramp voltage to said first reference voltage, the unknown input voltage, and said second reference voltage; means for generating regularly spaced pulses; counter means responsive to the output from said pulse generating means for counting the number of pulses generated in a reference time interval between the coincidence of said ramp voltage with said first and said second reference voltages; feedback means responsive to said counter means and said comparing means for controlling the frequency of said pulse generating means to maintain the number of said pulses in the reference time interval at a predetermined number; means for gating a portion of the output of said pulse generating means to a digital display device in response to the coincidence of said ramp voltage with said unknown input voltage and in response to an output from said counter means representing one-half of said predetermined number of pulses thereby to provide a number of pulses to the display device which is a direct function of the magnitude of the voltage of said unknown input with respect to zero; and means for determining the sequence of occurrence of the coincidence of the ramp voltage with said unknown input and the output from said counter representing one-half said predetermined number of pulses to provide an indication of the polarity of the unknown input.

Claim 16

The measuring circuit of claim 12 further including means for clamping said pulse generating means into a nonoscillating state prior to said reference time interval and for gating said pulse generating means into operation upon the coincidence of said ramp voltage with said first reference voltage so that the phase of the output of said pulse generating means at the beginning of said reference time interval is the same for each voltage measurement.