Browse Prior Art Database

Four-Speed Transmission for Processor Clock Start

IP.com Disclosure Number: IPCOM000114619D
Original Publication Date: 1995-Jan-01
Included in the Prior Art Database: 2005-Mar-29
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Johnson, CL: AUTHOR [+4]

Abstract

A method of starting clocks on a Complementary Metal-Oxide Semiconductor (CMOS) processor that avoids a di/dt noise problem is disclosed. Clocks are started using an automatic transmission which consists of a series of gears that successively ramp-up clock frequencies until full clock speed is achieved.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 65% of the total text.

Four-Speed Transmission for Processor Clock Start

      A method of starting clocks on a Complementary Metal-Oxide
Semiconductor (CMOS) processor that avoids a di/dt noise problem is
disclosed.  Clocks are started using an automatic transmission which
consists of a series of gears that successively ramp-up clock
frequencies until full clock speed is achieved.

      Computer processors designed in CMOS do not require any
significant current when there are no circuits switching.  This is
generally the case when the input oscillator or clocks are turned
off.  When clocks are turned on, the instantaneous current required
by a processor can jump significantly to its full steady state value.
Even though the processor may not immediately start executing
instructions, this instantaneous current requirement can be large
because the clock circuits alone account for much of the chips
switching activity.  As integrated circuit chips get bigger and
denser, this steady state current requirement can be significant.
Due to inherent inductance in chip pins and wiring on the next level
of packaging, there is a limit to the instantaneous change in
current, known as di/dt.  Because of this limit, the internal voltage
on the chip can drop below the point at which logic gates function
properly.

      The transmission starts clocks at a frequency that is lower
than the time constant of the power distribution system.  At the
reduced clock frequency there is a series of small in...