Analog to digital converter

A device for converting a signal voltage into a multi-bit digital word that defines the voltage magnitude and polarity is described. The input voltage V to be digitized is used to control the frequency of a voltage controlled oscillator, whose output is defined to be f=fo+kV. The signal out of the voltage controlled oscillator is fed to differential delay line filters that permit all digits to be derived in parallel. The filters comprise pairs of delay lines of unequal length, each pair feeding a respective phase detector whose output is amplified, diode-rectified and limited. To increase the accuracy of this device, an automatic frequency control loop can be incorporated to control fo. This loop zeros V occassionally and reads the output digital word to measure the frequency error and add a correcting voltage to the input voltage V when it is not zeroed for the measurement.