awpaeth@watcgl.waterloo.edu (Alan Wm Paeth) (09/21/89)
In <1989Sep19.171259.1670@mentor.com> mbutts@mentor.com (Mike Butts) writes: >The current Electronic Design (9/14/89) has a piece on the new Burr-Brown >PCM1705P, a monolithic dual analog-to-digital converter. It runs at 200 kHz, >gives 14-bit accuracy and 18-bit resolution, and costs $27 in 1K quantity (I'd >guess <$50 in onesies)... >Imagine how fast, cheap ADCs and DSPs could cause a revolution in receiver >design (especially when we get cheap ADCs and DSPs that can handle several >MHz IFs, and direct digital synth chips to match)... I like this approach. I've been waiting for a cheap part for some time -- forget for a moment the use of the chip in post-IF demodulation consider direct conversion of VLF. A WWVB receiver at 60kHz which is nearly all-digital is quite possible. No IF needed, the LC tank/antenna coupling at the front end represent the only analog parts (and reduce multiples of 60kHz to the point that there are not aliasing/fold-over effects to corrupt the ADC samples). Then what remains is a fast ADC and fast digital processor, for which 60kHz is not impossibly fast. The two other interesting part of the project is that because the time info modulation is done by carrier phase shifts, one wants synchronous AM detection. Also, the BCD datastream recovered needs to be turned into ASCII or used to drive a display. The former is done easily with digital signal processing techniques, the latter by simple data processing. I would love to see an inexpensive two chip (ADC+CPU) solution. /Alan Paeth Computer Graphics Laboratory University of Waterloo