Use of a chopper and a sigma-delta modulator for downconverting and digitizing an analog signal including information modulated by a carrier
US5459432A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 20, 1995 |
| Grant date | Oct 17, 1995 |
| Priority date | — |
| Expiry date | Jan 20, 2015 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03D1/00
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
To demodulate an analog signal having information modulated by a carrier, the analog signal is chopped by a chopper, the chopped signal is digitized by a sigma-delta analog-to-digital converter to produce a series of digital samples at a sampling frequency, the digital samples are filtered in a digital decimating filter to produce data words, and the data words are modulated by an intermediate frequency signal to produce a detected information signal. The various frequency signals are generated by a phase-lock loop so that the intermediate frequency is the difference between the carrier frequency and the chopping frequency, and both the chopping frequency and the intermediate frequency are sub-multiples of the sampling frequency. Therefore aliases and artifacts caused by the chopper are either cancelled or fall on multiples of the output sampling frequency, and the intermediate frequency signal can be a square wave without generating artifacts that need be removed by filtering of the detected information signal. Preferably the chopper is placed in an analog portion of a feedback loop of the sigma-delta modulator, and an exclusive-OR gate is placed in the digital portion of the feed…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.