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Voltage Level Translation Circuit

IP.com Disclosure Number: IPCOM000083520D
Original Publication Date: 1975-Jun-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Gersbach, JE: AUTHOR

Abstract

The circuit shown provides voltage level translation of a small signal at a high (Lambda 5V) level to a large (or small) signal at a low level (near ground), while avoiding the saturation of the driving NPN transistor and the inherent poor gain of a lateral PNP transistor in a NPN silicon technology.

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Voltage Level Translation Circuit

The circuit shown provides voltage level translation of a small signal at a high (Lambda 5V) level to a large (or small) signal at a low level (near ground), while avoiding the saturation of the driving NPN transistor and the inherent poor gain of a lateral PNP transistor in a NPN silicon technology.

Vin is driven from the collector of a NPN transistor whose base is at +V. The signal swing is, therefore, limited to less than 0.8 volt. A PNP inverter requires more than 0.8 volt if the current is to be controlled through an emitter resistor.

The circuit shown provides a well regulated current in the PNP stage while avoiding saturation of T2. When Vin is at +V, all of the current i1 flows in T1. T2 is off, since the base of T2 is held negative by a value of i2 X (R1 + R2). When Vin is negative with respect to +V, the feedback loop comprised of T2, R2, and T3 is active. T3's emitter current is then equal to Vin i2R2 over R1 i2.

The base of T2 is about equal to Vin and assuming Vbe 2 = Vbe 3, T2 is out of saturation by a voltage equal to i2R2. Since the emitter current of T3 is well defined by the feedback loop and Vin, the loss or uncertainty of T3's collector current is determined by the grounded base current gain, rather than the grounded emitter current gain beta and has a relatively small variation.

To further improve this tolerance, the collector of T4 may be fed back to the emitter of T3 and the output taken from the emitter of...