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Precision Integrated Bandgap BIAS Cell With High Psrr

IP.com Disclosure Number: IPCOM000035785D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Buchholtz, TC: AUTHOR [+3]

Abstract

A general-purpose bias cell is here used on analog/digital BIFET standard cells and master image designs. Its novel circuit design implementation provides a high precision (2.3 V +/- 3%), temperature compensated (<50 ppm/degrees C) on- or off-chip reference voltage, a temperature compensated reference current, and temperature compensated, accurate bias voltages for NFET, PFET, and NPN current sources. The novel design implementation provides for a high power supply rejection ratio of typically 80 dB at low frequencies.

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Precision Integrated Bandgap BIAS Cell With High Psrr

A general-purpose bias cell is here used on analog/digital BIFET standard cells and master image designs. Its novel circuit design implementation provides a high precision (2.3 V +/- 3%), temperature compensated (<50 ppm/degrees C) on- or off-chip reference voltage, a temperature compensated reference current, and temperature compensated, accurate bias voltages for NFET, PFET, and NPN current sources. The novel design implementation provides for a high power supply rejection ratio of typically 80 dB at low frequencies.

The figure shows a schematic of the BIAS cell. On the left side of the figure, PFET current source T1 and diode-connected transistors Q17 through Q20 provide a start-up voltage to the base of Q5 and a pre-regulated voltage to the first stage bandgap circuit thru Q6, Q7, and Q8 represents the input of a feedback amplifier, whose output drives the base of Q1 that maintains equal voltage across R5 and R6. This, in turn, guarantees equal current through R5 and R6. Thus, Q1 carries exactly three times the collector current of each of Q2 through Q4. This puts a VT LN(3) positive temperature coefficient voltage across R1 through R3. Note that VT is KT/Q where k is Boltzmann's constant, T is the temperature in degrees Kelvin, and Q is the electronic charge in coulombs. LN refers to the natural logarithm. The R3/R4 ratio is chosen so that the bandgap voltage of 1.23 volts is produced at zero temperature coefficient at the base of Q1. The pre- regulation at R5 and R6 prevents the power supply from modulating the collector to emitter drop of Q1 through Q4 and thus also their base to emitter drops. R7 compensates the beta difference between Q1 and Q2 through Q4, since they are at different emitter currents. R9 and R8 produce a multiple of the bandgap voltage at node 15. This voltage is 2.3 V +/-3% with <50 ppm/degrees C temperature coefficient.

Since R5 and R6 are referenced three diode drops above ground, the drain to source voltage across T6 is basically power supply independent. The feedback amplifier with inputs at the base of Q7 and Q8 obtains its b...