GB1436851A - Analog-to-digital-converter - Google Patents

Abstract

1436851 Analogue to digital converter GENERAL ELECTRIC CO 12 June 1973 [21 June 1972] 27986/73 Heading H3H An analogue to digital converter comprises a voltage to frequency converter 14 to which the unknown voltage V x and a feedback voltage are fed in opposition, a phase detector 18 determining the phase difference between the output of converter 14 and a reference oscillator 20, in the form of a train of duration (mark/space) signals, a low pass filter 26 which generates the feedback analogue voltage from the mark/ space signal and a counter 30 which counts clock pulses for the duration of the duration signal to provide the digital output. As described, the unknown voltage V x is supplied via resistor R i and after subtraction of the feedback voltage via resistor R j , provides an input V Q to the voltage controlled oscillator 14. The output frequency is divided by N at 16 and the pulses are squared and fed to the phase detector 18. The output of an oscillator 20 controlled by reference voltage V R is divided by M and fed to the phase detector 18. The phase detector output after filtering is fed back to complete the phase locked loop which alters V Q until the phase detector input frequencies are the same. The phase difference duration pulses gate pulses from oscillator 20 to a counter 30, which may be preset to a desired count and the count, which is regenerated for each phase detector duration output may be transferred to a holding register 32. The converter may be produced as an integrated circuit, the frequencies of the oscillators being different to prevent interaction.