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Re: [Discuss-gnuradio] IF ADC, and the radio itself

From: David Bengtson
Subject: Re: [Discuss-gnuradio] IF ADC, and the radio itself
Date: Mon, 10 Mar 2003 22:21:46 -0500

On Mon, 10 Mar 2003 10:15:11 -0800, you wrote:

>Akshay mentioned Maxim ADCs for IF sampling -- here's a link to the
>front-end of Maxim's parametric search page for high-speed ADCs. You can
>either 'show all products' or drill-down to filter out only the ones with
>full-power BW, ENOB, etc that you want. 
>Of particular interest are the MAX104/106/108 family... probably over-kill
>for any real IF sampling, but they offer 600 to 1500 Msps (yes,
>1.5giga-sample per second) with the analog front end to match this
>performance (2.2GHz FullPower BW).
>Have any comm buffs out there laid down minimum required specs for things
>like Spurious-Free-Dynamic-Range (SFDR), Signal-to-Noise-ratio+distortion
>(SINAD), or effective-number-of-bits (ENOB) ?  The IF itself will tell us
>what the input BW needs to be, and Nyquist  will tell us what the sample
>rate needs to be.

Part of the problem is that the front end spec's are undefined since
modes and protocols are a bit undefined. it would probably be possible
to come up with some band level specs, for a "broadband" (Think CDMA)
and a "narrowband" (think GSM and AMPS, iDEN, LMRS). I'm not
conversant with the various video modes. Coming up with a list of
potential target protocols/modes is a starting point. 
>Just to clarify one point -- hardware folks here are expecting to
>under-sample the IF, right, not try to grab _everything_ from DC to 500+
>MHz?  There was a comment a while back that sounded like people were talking
>about needing to sample a 300MHz IF at more than 600Msps -- remember that
>Nyquist under-sampling will effectively mix down for us, so the sample rate
>only needs to be 2x the actual BW used at IF, since that's the only info
>we're interested in.  ...and this is assuming we're going to provide
>ourselve's the opportunity to grab every channel in the band. Sorry if I'm
>just stating the obvious.

Undersampling makes some of this easier. However, you still have to
have a bandpass filter in from of the ADC to protect against sampling
images. Grabbing everything in a band is a probably too
computationally expensive for a 3 to 5 years. 

>In this light, the MAX 1180 and 1190-series (there are about a dozen in
>these families) all have input track/hold stages worth about 400MHz, with
>sample rates anywhere from 10Msps to about 100Msps, all 10-bit res... see
>that parametric search page for more details.  Most cellular handsets use
>IFs in the range of 100MHz to 300MHz, and the widest receive band is only
>60MHz (UMTS, US PCS), so just in these respects, these ADCs should be a good
>match. Frankly, the target application for most of Maxim's high-speed ADCs
>are as basestation IF sampling, so they ought to do well for cellular
>For HDTV, the specs might be similar, since we're only grabbing a single
>channel... can someone post what they know about HDTV's modulation scheme?
>A quick question about the radio itself -- most of the conversation here is
>about the software implementation of the SDR, and very little about the
>radio front-end (how we get from RF to IF).  What are people's plans here
>for desiging the radio?  I'm a junior RF guy (only 5 years out of school),
>but I'd like to contribute to this part of the effort if I can. 
>Brian Whitaker
>Maxim RF Applications

Brian, I think this would make a hella app not for Maxim.........


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