Re: Analog memories

On Fri, 17 Jun 2005 23:17:58 GMT, "TheDoc" <TheDoc@xxxxxxx> wrote:

> ...

>Thanks for the input.. however I did omit one thing.. LOW power...

OH! Well, that's different...

>I know there are fast ADC's to do this job, and I am experienced with
>megasample systems, but I was looking for an alternative solution so I
>could used a low power micro such as the msp430.. i have a severe power
>budget to contend with
>that I am unable to meet with a more conventional approach..

Then perhaps my CMOS analog-switch idea is just the thing. Looks
like digikey has 74hc4067's (16 to 1 analog MUXes), and they're cheap
enough in quantity, so buy two for each unit. :) Use a 4066-type
switch to connect the switch array to the input which you sample at
1MSPS, then switch it out and then (using another 1/4 4066) switch in
your A/D (if its input impedance is too low you'll need another buffer
here, in addition to the one described below), to which you 'play
back' the values at 200kSPS.
There's some "design considerations" on the analog side of this
thing. If what you're reading doesn't have a low enough output
impedance, you'll need an op-amp buffer between it and this
switched-capacitor idea, and the op-amp will have to provide enough
current to charge each cap to the current signal's level, which may
exceed your power budget. The capacitors obviously need to be scaled
to be large enough to hold to 12-bit accuracy between sampling and
being read back (worst case, 200kSPS @ 16 samples = 80 microseconds),
but not so large as to create an unnecesarry load to the buffer.
I don't know of a single chip to do this sort of thing, but you
might ask with a careful crosspost to sci.electronics.design and
sci.electronics.components, where other knowledgable people who don't
read here may have some good ideas.

>thanks


-----
http://www.mindspring.com/~benbradley
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