Browse Prior Art Database

BI-CMOS Output Buffer Slope Control With Compensated Voltage Reference

IP.com Disclosure Number: IPCOM000099687D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Boudon, G: AUTHOR [+3]

Abstract

This invention relates to a BI-CMOS off-chip driver (OCD) featuring a slope control circuit which allows having an output signal rise and fall time almost constant through power supply, temperature and process variations.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 72% of the total text.

BI-CMOS Output Buffer Slope Control With Compensated Voltage Reference

       This invention relates to a BI-CMOS off-chip driver (OCD)
featuring a slope control circuit which allows having an output
signal rise and fall time almost constant through power supply,
temperature and process variations.

      A schematic of the circuit is shown in the drawing.

      The BI-CMOS OCD is composed of CMOS front-end circuit (T3,T4,
T7,T8) and a pair of bipolar transistors (T1,T2), connected as a
push-pull output buffer.  The pull down NPN device is controlled by
NFET T3. The NFET T4, used as a resistor, has its gate biased by a
compensated reference voltage (CVref). The current (I4) through T4,
feeding the base of T1, depends on the CVref value.

      This CVref circuit is made with a NPN device (T5), a NFET (T6),
and three resistors (R1,R2,R3).

      When the power supply (Vh) voltage decreases, the current
through R1,T6 decreases, CVref increases, so that the current I4
increases.  Consequently, the impact on delay, due to Vh voltage
variation, will be reduced.

      The current gain (Beta) of the NPN devices and the
transconductance (Gamma) of FET vary with process parameters and
temperature.  When Beta is high, the current through R1 increases,
CVref decreases, as well as I4. This will prevent the output current
from exceeding the expected value and hence generating noise on the
chip. In a similar way, when Gamma increases, CVref becomes lower,
th...