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Trim Circuit for Precision Current Source Matching

IP.com Disclosure Number: IPCOM000040907D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Lobb, KG: AUTHOR [+2]

Abstract

The trim circuit illustrates a method to obtain precision matching for current sources using active trimmed resistors either on a semiconductor chip or in a hybrid circuit package.

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Trim Circuit for Precision Current Source Matching

The trim circuit illustrates a method to obtain precision matching for current sources using active trimmed resistors either on a semiconductor chip or in a hybrid circuit package.

Referring to the figure, a temperature compensated reference voltage '1' is applied to the base of current source transistors 'Tl' through 'Tn'. This current is then mirrored by PNP transistors. Transistor 'TPm', the mirror reference device, is twice the size of transistors 'TPl' through 'TPn'. Thus the current of 'TPl' through 'TPn' is one-fourth of 'Il ' through 'In'. By passively trimming 'RT', and then actively trimming '2RT', a perfect match can be achieved for 'Il' through 'In'. The matching achieved is independent of the reference voltage 'l', and thus can be used in high resolution (digital-to-analog converters) where 'l' controls the full scale gain, or is the multiplier input.

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