US5245632A
Expired / Lapsed
US
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Synchronous FSK detection
Assignee: National Semiconductor Corp
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Filing: 1992-05-19
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Granted: 1993-09-14
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Expires: 2012-05-19
Abstract
Abstract The present invention provides methods and apparatus for synchronous detection of a Frequency Shift Keying (FSK) signal. The demodulation of the FSK signal is performed in the "complex plane" after multiplying the input samples by an unlocked complex carrier in a complex down converter. Two decision bits are generated per real bit. Once bit should be the real decision; the other bit is a "transition" bit between two Bauds. To generate this situation, the last three decisions are considered. If a transition from 0 to 1, or vice-versa, occurs between the first and third bit, then the middle (second) bit should have equal probability to be 0 or 1. If it is 1, timing correction, by moving the sampling window, is done towards the 0 bit. If it is a 0, the sampling window is moved toward the 1 bit. The timing decision is efficiently implemented by taking the three bits as an index to an 8-entry look-up table that generates ADVANCE, DELAY or NO --OP directions.
Inventors
- 👤 Israel Greiss
- 👤 Eran Gluska
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 12:51
CPC Classifications
H; H04; H04L; H04L7/00; H04L7/02; H04L7/033; H04L7/0334; H04L27/00; H04L27/10; H04L27/14; H04L27/144; H04L27/152; H04L27/1525; H04L7/0331
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
120 words
A method for synchronously detecting data in a Frequency Shift Keying (FSK) signal that comprises successively transmitted symbols every symbol time period T using two baseband point per symbol, the method comprising: (a) down-converting the FSK signal to a complex baseband signal; (b) sampling the complex baseband signal at a plurality of complex points per symbol time period T to provide a plurality of complex samples; (c) combining the complex samples to provide a complex result every one-half symbol period T/2; (d) taking the sign of the complex result to provide a corresponding sign bit; and (e) utilizing the sign bits of the current result and the two immediately preceding results to generate commands for controlling the down-converting step (a).
Claim 2
Independent Claim
120 words
A method for synchronously detecting data in a Frequency Shift Keying (FSK) signal that comprises successively transmitted symbols every symbol time period T using two baseband point per symbol, the method comprising: (a) down-converting the FSK signal to a complex baseband signal; (b) sampling the complex baseband signal at a plurality of complex points per symbol time period T to provide a plurality of complex samples; (c) combining the complex samples to provide a complex result every one-half symbol period T/2; (d) taking the sign of the complex result to provide a corresponding sign bit; and (e) utilizing the sign bits of the current result and the two immediately preceding results to generate commands for controlling the down-converting step (a).
Claim 3
Dependent Claim
130 words
Apparatus for synchronously detecting data in a FSK signal that comprises successively transmitted symbols every symbol time period T, the apparatus comprising: (a) a complex down-converter for down-converting the FSK signal to a complex baseband signal; (b) means for sampling the complex baseband signal at a plurality of complex points per symbol time period T to provide a plurality of complex samples; (c) means for combining the complex samples to provide a complex result every one-half symbol time period T/2; (d) means for taking the sign of the complex result to provide a corresponding sign bit; and (e) a command generator responsive to the sign bits of the current result and the two immediately preceding results for issuing control commands to the complex down-converter for advancing or delaying the down-converter.
Claim 4
Dependent Claim
130 words
Apparatus for synchronously detecting data in a FSK signal that comprises successively transmitted symbols every symbol time period T, the apparatus comprising: (a) a complex down-converter for down-converting the FSK signal to a complex baseband signal; (b) means for sampling the complex baseband signal at a plurality of complex points per symbol time period T to provide a plurality of complex samples; (c) means for combining the complex samples to provide a complex result every one-half symbol time period T/2; (d) means for taking the sign of the complex result to provide a corresponding sign bit; and (e) a command generator responsive to the sign bits of the current result and the two immediately preceding results for issuing control commands to the complex down-converter for advancing or delaying the down-converter.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1996-09-13 | 1997-03-15 | 1997-09-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2000-09-13 | 2001-03-15 | 2001-09-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2004-09-13 | 2005-03-15 | 2005-09-14 | $7700.00 | Window Closed / Lapsed |