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Temperature Compensated Current Source

IP.com Disclosure Number: IPCOM000093804D
Original Publication Date: 1966-Feb-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Bakke, EP: AUTHOR [+2]

Abstract

Operating current is supplied to the base of input transistor 3 of operational amplifier 2 by current source 1 comprising voltage divider network R1, R2, R3 and R4. The network is temperature compensated by forward biased diodes 4. To enable accurate matching of the current supplied by 1 to the current required by 3, diodes 4 are, for example, of mixed characteristics one being silicon and two being germanium. While the voltage gradient due to temperature change is substantially the same for both types of diodes the absolute voltage drops across each type of diode at a given current level is quite different. Therefore by cascading the desired number and mixture of silicon and germanium diodes, the resistance of 4 and thus the overall temperature-voltage gradient of 1 can be realized within a wide range of values.

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Temperature Compensated Current Source

Operating current is supplied to the base of input transistor 3 of operational amplifier 2 by current source 1 comprising voltage divider network R1, R2, R3 and R4. The network is temperature compensated by forward biased diodes 4. To enable accurate matching of the current supplied by 1 to the current required by 3, diodes 4 are, for example, of mixed characteristics one being silicon and two being germanium. While the voltage gradient due to temperature change is substantially the same for both types of diodes the absolute voltage drops across each type of diode at a given current level is quite different. Therefore by cascading the desired number and mixture of silicon and germanium diodes, the resistance of 4 and thus the overall temperature-voltage gradient of 1 can be realized within a wide range of values. This enables very accurate matching of the current supplied by 1 to that used by 3 over a given temperature range.

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