[sdiy] 3/4 bit A/D converter (was: Sample&Hold thoughts)

[Grant Richter]

The comparator string used to be call a "thermometer" circuit. Now I suppose
it is a "bargraph" circuit. You can use one or more CD4582 priority encoders
on the output to make a X bit flash A/D (maybe 100kHz bandwidth). Pretty
cheap, sorta fast.

The $35 RCA flash converters with a few megahertz BW do this by stacking
comparators (64 or 256) on the chip with a priority encoder. Very fast, not
cheap.

Johns circuit is more like a neural net. The comparator thresholds are
modulated by the output state. As such, it is a more like a "ripple"
converter. There are going to be brief false outputs before it settles on
the correct answer.

> From: KA4HJH <ka4hjh at gte.net>
> Reply-To: owner-synth-diy at node12b53.a2000.nl
> Date: Thu, 15 Mar 2001 01:26:48 -0500
> To: synth-diy at node12b53.a2000.nl
> Subject: Re: [sdiy] 3/4 bit A/D converter (was: Sample&Hold thoughts)
> 
>> If you use LM319 comparators and put RGB video through it, it produces an
>> effect called "posturization" or fixing of the color levels. This was used
>> in the Sandin Image Processor. The output summing resistors can be replaced
>> with pots for variable levels.
> 
> I wonder how this approach compares with John Simonton's 4 bit flash
> converter? (only 4 opamps). Is this faster? How much?
> 
> -- 
> Terry Bowman, KA4HJH
> "The Mac Doctor"
>