On 4/3/2015 9:07 PM, Tim Williams wrote:
"John Larkin" wrote in message
...
Classic flash ADCs used 2^n comparators and a resistor string in the
front end. The resulting (say, 256 bit) thermomometer code was then
mapped into binary. I think somebody did that at 10 bits, 1024
comparators.

Nowadays people tend to do cleverer things.

Are they still de rigeur for the bleedingest of edges in the Hittite and
etc. catalogs?

Pipelined SAR has certainly come a long way since the olden days.

Flash converters are the only choice for anything above around 1-2 MSPS
last time I looked hard. Maybe they are pushing towards 10 MSPS with
SARS and SD converters. But for anything higher a flash converter is
the only choice.

That said, there are different forms of flash converters. Up to about
8-10 bits all that I have seen were single stage. But by the time you
reach 10 bits the number of comparators becomes unwieldy. For high bit
counts or for lower power they use subranging with a pair of lower bit
count flash converters, one with low resolution for the upper bits and
one with high resolution for the lower bits. Essentially this is a
hybrid of the flash converter and an SAR. To deal with the
imperfections in matching the two it is common to have an overlap in the
number of bits used. These are are the bleeding edge devices providing
flash like performance at up to 16 bit resolution.

But for the highest sample rates the direct flash converter is your
huckleberry.

--

Rick