[hpsdr] HORTON

[John B. Stephensen]

Look at the TI ADS1601-1626 delta-sigma ADCs. These are 16-18 bits and
support 1.25-10 Msps. IMD is as low as -98 dB at 500 kHz and the price is a
low as $15.

73,

John
KD6OZH

----- Original Message ----- 
From: "Eric Blossom" <eb at comsec.com>
To: <hpsdr at hpsdr.org>
Sent: Saturday, June 10, 2006 20:02 UTC
Subject: [hpsdr] HORTON


> ***** High Performance Software Defined Radio Discussion List *****
>
> I've been doing some thinking about HORTON.
>
> It seems to me that the biggest problem with getting the QSD to run
> fast is finding switches/muxes that are fast enough.
>
> In my searching, the fastest CMOS FET mux I've come across to date
> is the TI SN74CB3Q3253.
> http://focus.ti.com/docs/prod/folders/print/sn74cb3q3253.html
>
> The problem with these isn't the "High-bandwidth data path (upto 500
MHz)",
> but rather it's the relatively slow speed at which you can switch
> them.  According the specs, this part maxes out at 20 MHz, but perhaps
> it could be pushed a bit past that.
>
> The ADG901 has a similar problem.  It's flat out past 1 GHz, but
> the typical switching time is 4.7ns (worst case 7.75ns: 129 MHz).
>
> I'm interested in getting a QSD running at at least 100 MHz, but why
> not try for 145 MHz while we're at it.
>
> To run at 100 MHz (passive radar application), the switches need to
> work at 400 MHz.  You're feeding it quadrature LO at the center freq,
> but the difference between I & Q is 90 degrees.
>
> Sythesizing the control of the switches shouldn't be a problem.  E.g.,
> use a DDS to generate the I & Q LO, filter, run that into one of the
> very nice ADI clock distribution parts (AD9511 and friends).  These
> will give us differential LVPECL out.  A bit of LVPECL fanout
> buffering and some AND/NAND ECL will generate the switch enable
> signals, no problem (modulo level translation).  We should be able to
> run this at 700 - 800 MHz, no problem.
>
> So, then we return to the original question: What's the fastest analog
> switch we can find?
>
> Are there faster FETs available in technologies other than CMOS?
> E.g., GaAs or SiGe?
>
> I don't think we need the signal path to be flat out past 150 MHz,
> but we do need them to switch quickly ;)
>
>
> Regarding the converter, the AD7762 (parallel) or AD7763 (serial) look
> like a better fit than the AD7760.  The '62 and '63 sample at 625kS/s
> (or lower, it's a delta-sigma part), with better dynamic range than
> the 7760.
>
>
> I'd like to end up with a system that contained 4 HORTONs, a board to
> generate the quadrature LO and sample clock for all 4 HORTONs, and
> some way to get it all back into the PC.
>
> Comments, suggestions, etc?
>
> Eric
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