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BICMOS Reference Generator Circuit That Tracks Band-Gap Voltage

IP.com Disclosure Number: IPCOM000120114D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Bonges, HA: AUTHOR [+3]

Abstract

This on-chip circuit provides a TTL voltage reference that tracks band-gap voltage. Having the reference voltage track the band-gap voltage prevents saturation of current source devices in current switch circuits using the reference voltage.

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BICMOS Reference Generator Circuit That Tracks Band-Gap Voltage

      This on-chip circuit provides a TTL voltage reference
that tracks band-gap voltage.  Having the reference voltage track the
band-gap voltage prevents saturation of current source devices in
current switch circuits using the reference voltage.

      Referring to the figure, voltage Vx from conventional band gap
generator circuit 2 is transformed to provide TTL voltage reference
VR.  Voltage at node A is made to be VA = Vx + 3Vbe/2 by
a base emitter voltage (Vbe) multiplier circuit comprised of NPN
transistor T1 and resistors R1 and R2.  P-type transistors T2 and T3
form a current mirror. Transistor T4 and resistor R3 form a constant
current source for the mirror which is driven by band-gap voltage Vx.
NPN transistor T5 is an emitter follower used to set reference
voltage VR = VA - Vbe = Vx + Vbe/2.  Voltage VR is not influenced
by chip temperature or high voltage supply voltage VH variation.

      Any current source device in a current switch circuit may now
be kept safely below saturation by using the band gap controlled
reference voltage VR.

      Note that voltage VR may be adjusted to suit noise margin
requirements and band gap voltage accuracy by appropriate sizing of
circuit elements shown.