Browse Prior Art Database

Power-On Bringup Circuit

IP.com Disclosure Number: IPCOM000117891D
Original Publication Date: 1996-Jul-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Gowda, S: AUTHOR [+5]

Abstract

Disclosed is a scheme that is used to ensure the state of logic internal to a chip when the power is turned on. In portable applications with small form factors, the chip designs are pin limited and do not permit the use of external signals for this purpose.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Power-On Bringup Circuit

      Disclosed is a scheme that is used to ensure the state of logic
internal to a chip when the power is turned on.  In portable
applications with small form factors, the chip designs are pin
limited and do not permit the use of external signals for this
purpose.

      The disclosed active circuit assures that the ouput of the
power-up circuit is in a known state until the power supply reaches a
stable voltage level, regardless of how slowly the power supply
voltage ramps up in time.  When the power supply has reached a level
at which the logic on the chip has settled, the output of the
power-up circuit switches state.

      Two embodiments of the disclosed circuit are shown in Figs. 1
and 2.  These two circuits operate similarly.  The initial state of
the circuit before the power is turned on is as follows: all
capacitors are discharged, the output of INV1 is low and the output
of INV2 is high.  As the power supply voltage increases, transistor
SW1 is used as a switch to charge capacitor C1 through resistor R1.
The circuit connected to the gate of SW1 is referred to as the switch
turn-on circuit.  The transistor SW1 acts as a very large, variable
resistor to delay the RC charging until the power supply voltage
reaches a threshold value set by the switch turn-on circuit.  The
function of the switch turn-on circuit is to ensure that the supply
voltage reaches a value at which the other logic on the chip is fully
functional, bef...