Filtered detection plus propagated timing window for stabilizing the switch from crystal to ring oscillator at power-down
US5140197A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Aug 13, 1990 |
| Grant date | Aug 18, 1992 |
| Priority date | — |
| Expiry date | Aug 13, 2010 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06F11/2015
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
An adjunct chip, usable as a peripheral to a microprocessor, which detects power failure, and puts the microprocessor into a known state upon power down. In order to reliably and stably put the microprocessor into a known state, several clocks are generated after the reset signal. However, since the power supply is failing, it is possible that the crystal-controlled oscillator may already have become unreliable. Therefore, a simple logic circuit (a ring oscillator, in the presently preferred embodiment) is used to generate the needed additional clocks at power-down. In the presently preferred embodiment, the switch from crystal-controlled oscillator to ring oscillator is stabilized by using a nonlinear filter circuit (driven by both the ring oscillator and the crystal oscillator) to detect when the crystal oscillator actually begins to fail. A transmission gate is then disabled, and the state frozen for long enough to allow any changes to propagate through.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.