Integrated circuit incorporating circuitry for determining which of at least two possible frequencies is present on an externally provided reference signal and method therefor
US6686803B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | Jul 10, 2001 |
| Grant date | Feb 3, 2004 |
| Priority date | — |
| Expiry date | Jan 3, 2022 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L7/033
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
An internal frequency reference, such as a VCO used in a PLL, having a free-running frequency fairly well controlled within a predictable range, is used as a rough frequency reference to determine, for an externally-provided frequency reference signal, which of a finite number of discrete frequencies is currently received. The VCO has a frequency range which varies less, as a percentage, than the ratio between possible reference frequency values. Consequently, the VCO is used as a frequency reference to measure the frequency reference signal. An internal signal is generated to indicate to remaining circuitry which of the possible reference frequencies is actually being provided, without requiring use of any dedicated input pins to receive a select signal. An integrated circuit device may be configured for different modes of operation as a function of which reference frequency is provided to the device. Moreover, if one of the available reference clock frequencies is chosen to correspond to an internal test mode, the device may be placed in a test mode without requiring any additional dedicated input pins for that purpose, either.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.