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Inverting Digital To Analog Converter

IP.com Disclosure Number: IPCOM000083369D
Original Publication Date: 1975-May-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Pezdirtz, KF: AUTHOR

Abstract

This unit operates essentially as a normal digital-to-analog (D/A) converter except that it transforms an input digital signal, which is proportional to a period, to an output analog DC level, which is proportional to the frequency of the input signal.

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Inverting Digital To Analog Converter

This unit operates essentially as a normal digital-to-analog (D/A) converter except that it transforms an input digital signal, which is proportional to a period, to an output analog DC level, which is proportional to the frequency of the input signal.

This inversion is accomplished by designing a parallel set of binary weighted resistors, so that the least significant bit (LSB) corresponds to the largest resistor and the most significant bit (MSB) corresponds to the smallest resistor. Thus the LSB input being on by itself, which would represent the smallest period or the highest frequency, would switch the largest resistance into the circuit. The MSB being on by itself, which would represent a long period or a very low frequency, would switch a very small resistor into the circuit.

If both the LSB and MSB were on, which would represent a small increase in the period, the largest and smallest resistors would be switched into parallel. The resultant parallel resistance, R(P), would be only slightly less than the smallest resistance by itself. In like fashion any combination of bits being on produces some resultant parallel resistance, R(P), which is proportional to the input frequency.

The binary values 1, 2...N stored in the register provide corresponding outputs via the 100K limiting resistors to corresponding transistor switches, such as T1, T2 and TN. The collector load resistors are selected as shown to have values R x 2/...