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Digital-To-Analog Converter N Bits + Sign, With Complementary Cmos Current Source, on Gate Arrays

IP.com Disclosure Number: IPCOM000061791D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Mone, P: AUTHOR [+2]

Abstract

This article describes the implementation of a n bit digital-to-analog converter (DAC) with input time-varying current and providing an output current of each polarity. The circuit consists of: -an input reference circuit which transforms the input current into two references voltages, -an array of binary weighted current sources which transforms the reference voltages back into an output current equal to n times the input current, and -two differential amplifiers. The figure shows a 3-bit + sign DAC as an example. The originality of the circuit is found in the current source which is composed of four transistors. Each one is part of the current source and makes its contribution to the matching of the current sources. However, the two bottom transistors are also used to switch the current sources according to the input code.

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Digital-To-Analog Converter N Bits + Sign, With Complementary Cmos Current Source, on Gate Arrays

This article describes the implementation of a n bit digital-to-analog converter (DAC) with input time-varying current and providing an output current of each polarity. The circuit consists of: -an input reference circuit which transforms the input current into two references voltages, -an array of binary weighted current sources which transforms the reference voltages back into an output current equal to n times the input current, and -two differential amplifiers. The figure shows a 3-bit + sign DAC as an example. The originality of the circuit is found in the current source which is composed of four transistors. Each one is part of the current source and makes its contribution to the matching of the current sources. However, the two bottom transistors are also used to switch the current sources according to the input code. To provide an output current either positive or negative, complementary PFET current sources are used, implemented in the same way as the NFET current sources. Hence, no operational amplifier and subsequent resistances are needed to perform this feature, as in the bipolar case. These current sources are also used in the reference circuit. As the current sources are identical, the circuit is independent to process variations. Moreover, no precision element is required for this circuit. However, these precision elements would not have been availabl...