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# Bias Driver Technique

IP.com Disclosure Number: IPCOM000093330D
Original Publication Date: 1967-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 26K

IBM

## Related People

Lloyd, RH: AUTHOR

## Abstract

This circuit generates a regulated voltage. The performance of an emitter-follower which is used to generate a regulated reference voltage depends largely on its output impedance. The lower this is made, the better the regulation. The output impedance depends in turn on the base impedance. That is, the lower the base impedance, the lower is the output impedance,

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Bias Driver Technique

This circuit generates a regulated voltage. The performance of an emitter- follower which is used to generate a regulated reference voltage depends largely on its output impedance. The lower this is made, the better the regulation. The output impedance depends in turn on the base impedance. That is, the lower the base impedance, the lower is the output impedance,

Where a regulated reference voltage is generated on an integrated circuit chip, the available power area and heat dissipation limit the value to which bias resistors 1 and 2 can be reduced. Furthermore, the frequency response of transistor T1 decreases at higher frequencies, tending to increase the output impedance. This frequency response problem is particularly difficult when the values of resistors 1 and 2 cannot be made any lower.

The output impedance of the circuit shown is Z(out) approx. = to re + Zb/ beta, where r(e) is the series emitter resistance, Z(b) is the impedance from the base to AC ground, and beta is the current gain of transistor T1 which decreases with increasing frequency. Z(b) can be reduced at high frequencies by increasing the capacitance between the base and ground.

Resistors 1 and 2 are fabricated by diffusion of a dopant into substrate semiconductor region 3 to provide opposite conductivity area 4. Region 3 is the circuit ground. The capacitance from base to ground can be increased by increasing the capacitance of resistors 1 and 2 to ground. The inclusion...