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Dumbbell Resistor Tolerance Compensation Circuit

IP.com Disclosure Number: IPCOM000085651D
Original Publication Date: 1976-May-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Lane, RD: AUTHOR [+2]

Abstract

The circuitry depicted in Fig. 1 uses differential amplifying techniques, with negative feedback, to control the bias voltage and, therefore, the tolerance variation of onchip dumbbell (pinch) resistors. The circuit uses an external precision bridging network, composed of 1% resistors on card, to provide the correct reference and bias voltage for both legs of an on-chip differential amplifier.

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Dumbbell Resistor Tolerance Compensation Circuit

The circuitry depicted in Fig. 1 uses differential amplifying techniques, with negative feedback, to control the bias voltage and, therefore, the tolerance variation of onchip dumbbell (pinch) resistors. The circuit uses an external precision bridging network, composed of 1% resistors on card, to provide the correct reference and bias voltage for both legs of an on-chip differential amplifier.

In addition, due to the nature of the bridge, the bias voltage is set equally at the amplifiers input terminals, and is independent of both power supply and resistor variations. Therefore, the large processing tolerance associated with dumbbell resistors (-60%) can be reduced to less than -10%.

The circuit operation can be explained by observing the voltage-current characteristics of Fig. 2. Note: by increasing the substrate bias of the dumbbell resistor its value can be increased, i.e., at a given voltage (1.6 volts) across the resistor, the current decreases as the substrate voltage increases, resulting in a resistance increase.

In Fig. 1, if the monitored dumbbell resistor R in the bridging network (1 per chip) increases in value due to processing variation, the voltage at node 1 (base of transistor T1) increases causing T1 to conduct a larger percentage of the amplifier current. This increase in current causes the collector of transistor T1 (output terminal) to move negative, resulting in a reduction of bias voltage on th...