Sunday, January 2, 2011

QAM modem IC?

While browsing some of the tapr HSMM information, including one of the message boards, I found a post referencing a very highly integrated modem IC for doing QAM data with an I/Q interface. Here is the post. and Here is the IC in question.

I'm going to quote from the webpage:
The CMX7163 QAM Modem is a low power half-duplex device supporting multiple channel spacings under host microcontroller (┬ÁC) control. Its Function Image™ (FI) is loaded to initialise the device and determine modulation types. 
The 7163FI-4.x supports 4-, 16- and 64-QAM modulations up to 96kbps in a 25kHz channel, with channel estimation and equalization to provide robust performance under realistic channel conditions. 
Flexible bit rates support a wide range of applications requiring a selectable bit rate and robustness.
 An integrated analogue interface supports 'direct connection' to zero IF I/Q radio transceivers with few external components; no external codecs are required.


The odd thing is the message board post quotes 64kbps in a 25khz channel but the chip maker's website says 96kbps. Obviously that'd be the 64QAM modulation. That's still very impressive, in my opinion. I'd love to see these incorporated into a design for a 440mhz or higher HSMM radio.

Just read the datasheet, you can do 96kbps with 64QAM, 64kbps with 16QAM and 32kbps with 4QAM. That is assuming 18,000 symbols/s (your baud rate). This falls well within the 19.6kilobaud limit on 2m but outside the bandwidth limit of 20khz. If you reduced the baud rate to 9000 symbols/s you'd take up half the bandwidth. It'd fit within the 56kilobaud/100khz limits in the 440 band just find though.

The downside is that these are only available in 64 pin packages, VQFN and LQFP. Small pins with little space inbetween but I've seen people who could solder it.

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