Abstract: An analog-digital converter includes a source of high frequency pulses comprising a variable frequency oscillator having an output frequency f which is a function of an analog condition. Also included is a source of a reference signal, preferably pulses, having a fixed frequency whose value is a fraction of the value of the frequency of the variable frequency oscillator. The first named souce also includes a counter-divider to which the output of the variable frequency oscillator is applied. The counter-divider has an output which is either f/N or f/N-M where N and M are whole integers and M is less than N. A phase comparator is responsive to the reference signal and to the output from the counter-divider for measuring the phase difference between the reference signal and the output pulses from the counter-divider.

Abstract: A system with improved signal-to-noise ratio for digitizing a representation of an analog condition comprises two oscillators for generating high frequency digital pulse signals, the frequencies of which are harmonically related one to the other. One of the oscillators responds to the analog condition to cause a shift in phase in its digital signal to cause phase differences between the digital pulse signals. The phase differences include quantizing errors having energy from D.C. to one half the frequency of said digital signals. A phase detector detects the phase differences. The detected phase differences are applied to a low-pass filter to produce a signal representative of phase error in a frequency band of interest. A phase modulator modulates the phase shifted digital signal in response to said signal representative of phase error to enhance the phase difference in said frequency band of interest.

Abstract: Methods and apparatus are described for generating a digital representation of an analog condition. In one method high-frequency digital signals are generated with the frequency of each signal being constant and the frequencies bearing a harmonic relationship one to the other. A representation of the analog condition is applied to cause a shift in phase in at least one of the digital signals. The digital signals are then compared to obtain a measure of the phase shift which is utilized to adjust the phase of the phase shifted signal toward its original phase condition. As a result of the measure of phase shift, there is generated a single weighed digital function which is representative of the amplitude of the adjustment utilized to return the phase shifted signal toward its original phase shifted condition. The single weighed digital function is applied to a low-pass digital filter to produce a multi-bit digital word representative of the instantaneous value of the analog condition.