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Selectable Voltage Sources With Accurate Difference

IP.com Disclosure Number: IPCOM000077866D
Original Publication Date: 1972-Oct-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Liu, CC: AUTHOR [+2]

Abstract

This circuit employs a technique for creating two or more independent voltage sources which have small but accurately determined differences in value. The differences in value are not particularly affected by changes in power supplies or temperature.

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Selectable Voltage Sources With Accurate Difference

This circuit employs a technique for creating two or more independent voltage sources which have small but accurately determined differences in value. The differences in value are not particularly affected by changes in power supplies or temperature.

Two or more diodes on the same integrated circuit chip, when biased at the same forward current, exhibit a very small difference in their voltage drop, typically less than five millivolts. The two diodes may be biased at different currents and the difference between their voltages will also exhibit a tight tolerance - since the current voltage curves of the diodes are parallel and very close together. In addition, since the diode current-voltage curve is steep, variations in bias current such as might be caused by varying bias resistance or power supplies have small affect on the difference between the two voltages. Since the diodes are all on the same chip, they are at the same temperature and vary the same with changes in temperature. Thus, changes in temperature have very little effect on the voltage difference. When two voltage sources with difference in value of 50 to 100 millivolts and a tight tolerance on the difference are needed, two diodes on the same integrated circuit chip biased at different currents may be used. If larger difference voltages are required, two or more diodes may be placed in series for each voltage source, as long as all are on the same chip. If more than two sources are needed, more than two sets of diodes may be used as long as all are on the same chip. The tolerances on the difference voltages, which may be obtained by using diodes as tracking voltage sources, is much better than may be obtained by using resistive voltage dividers even if one percent resistors are used, since the voltage differences are only several percent of the power supply levels.

The figure shows the schematic diagram of the Integrated Circuit Read Channel Gate Generator circuit using the concept described. In this gate generator circuit a differential AC signal, about 1.5 volts peak-to-peak (differential measurement), is applied to the data inputs (IN1 and IN2). The signal is AC coupled through capacitors C1 and C2, with a DC bias determined by the potential at point V1, the cathode of D2. Voltage potential at V1 is also applied to the base of transistor T4. In normal operation, the control input at the base of transistor T1 is at a down level and the current switch transistors T1 and T2 have T2 co...