Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site unccvax.UUCP
Path: utzoo!linus!decvax!mcnc!unccvax!dsi
From: dsi@unccvax.UUCP (Dataspan Inc)
Newsgroups: net.analog
Subject: Re: Sugestions for flash ADC needed
Message-ID: <235@unccvax.UUCP>
Date: Sat, 20-Jul-85 12:02:02 EDT
Article-I.D.: unccvax.235
Posted: Sat Jul 20 12:02:02 1985
Date-Received: Tue, 23-Jul-85 05:31:34 EDT
References: <28450@lanl.ARPA>, <28485@lanl.ARPA>
Organization: UNC-Charlotte
Lines: 42


    You don't want much, do you? 100 mHz, 8 bits, and low power consumption?
RCA's SOS (silicon on sapphire) 8 bit converter can barely hit 14.318 mc;
in fact, this product may be stillborn.

    The TRW TDC1007 (and kin) aren't even fast enough. Do what we do. . .
get a bunch of TDC1025's (which are 50 mHz conversion rate) and drive them
with opposite phase clocks.  The aperture time of a TDC1025 is 40 picoseconds,
which is excellent; worst case time multiplexing error is still about 15 times
less than the sampling frequency required.

    YOU NEED A SAMPLE AND HOLD AMPLIFIER IN FRONT OF THIS THING TO MAKE IT
WORK RIGHT. Even at 50 mHz clock frequency, the full power guaranteed conversion

frequency is only 12.5 mHz. However, you can probably approach theoretical
limits with an Analog Devices HTS-0010 S/H amplifier; it has a 5 ps aperture
error.

    Have fun designing the driver amplifier for two A/D converters; the
input impedance is highly flaky on these converters.  Those high frequencies
will bring a new meaning to the term 'thermal tail'... about power consumption,
well, two TDC1025's eat a bunch of power. Be prepared to dissipate about 
8 watts of heat from the cases.

    Another alternative (for the strong-stomached) is to use 4 TDC1029
6 bit converters in the appropriate arrangement. They do 100 mHz and are
guaranteed to do full power quantization at 50 mHz.

    Finally, Sony supposedly has a 100 mHz 8-bit A/D in a single package,
but I've yet to see a data sheet.

    I wish you lots of luck.  Even Computer Labs (Analog Devices) hasn't 
taken this one on (commercially) yet. I hope you also have a very big 
budget for all the neat test equipment you are going to have to build and
buy.


David Anthony
Chief Development Engineer
DataSpan, Inc (the Southeast's largest user of TRW A/D converters!)

.