Flash ADC encoder logic equations

Could some DSP or electronics guru please direct me ? I am trying to
get hold of a typical (some standard number of resolution bits)  flash
ADC encoder logic equations.  Any hints, pointers would be very
valuable. Thanks in advance for your help.

It's not really clear what you are trying to do - make a flash ADC from scratch or interface to one with an FPGA or some such.

If the former, try
http://lmgtfy.com/?q=flash+adc to understand how one works.
There's also some useful visuals if you search for images:
http://www.google.ca/images?q=flash%20ADC
You should be able to generalize that information to understand how to make one for an arbitrary resolution.

If the latter, grab a data sheet for your ADC of choice (at this point whether it's a flash ADC or otherwise it doesn't matter) and start staring at the formatting of the output data.

Chris

On 03/29/2011 11:54 PM, Daku wrote:
> Could some DSP or electronics guru please direct me ? I am trying to
> get hold of a typical (some standard number of resolution bits)  flash
> ADC encoder logic equations.  Any hints, pointers would be very
> valuable. Thanks in advance for your help.

There may be some tricks, but basically a flash encoder with N bits has 
2^N - 1 comparators, that will go off in a pattern of
[[M ones] [2^N - M - 1 zeros]].  The logic is just a matter of 
accurately counting to M, probably while also ignoring patterns that go
[1 1 ... 1 1 0 1 0 0 ... 0 0] or similar.

Have you googled "flash ADC circuit" yet?

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

The circuit(ignoring pathological cases) is very similar to a priority enco=
der (Q.V.). of N lines in, the numeric code for the highest-priority one is=
 delivered. The circuit can be parallel or ripple-through and is often a co=
mbination of both. You could use a number of 74148s as the logic of a flash=
 ADC.

Jerry
--=20
Engineering is the art of making what you want from things you can get.

Daku wrote:

> Could some DSP or electronics guru please direct me ? I am trying to
> get hold of a typical (some standard number of resolution bits)  flash
> ADC encoder logic equations.  Any hints, pointers would be very
> valuable. Thanks in advance for your help.
You talking about a digital potentiometer?

  The way your question is formatted "Flash", that is the only thing I
can think of.

  For the resolution count.

  Res = 2^NumberOfBits;

a 12 bit ADC is common in basic set ups, that would = 4096 different
values.

  If you're talking about something else, you got me?
  Etc.

Jamie

On Mar 30, 9:16=A0am, Tim Wescott <t...@seemywebsite.com> wrote:
> On 03/29/2011 11:54 PM, Daku wrote:
>
> > Could some DSP or electronics guru please direct me ? I am trying to
> > get hold of a typical (some standard number of resolution bits) =A0flas=
h
> > ADC encoder logic equations. =A0Any hints, pointers would be very
> > valuable. Thanks in advance for your help.
>
> There may be some tricks, but basically a flash encoder with N bits has
> 2^N - 1 comparators, that will go off in a pattern of
> [[M ones] [2^N - M - 1 zeros]]. =A0The logic is just a matter of
> accurately counting to M, probably while also ignoring patterns that go
> [1 1 ... 1 1 0 1 0 0 ... 0 0] or similar.
>
> Have you googled "flash ADC circuit" yet?
>
> --
>
> Tim Wescott
> Wescott Design Serviceshttp://www.wescottdesign.com
>
> Do you need to implement control loops in software?
> "Applied Control Theory for Embedded Systems" was written for you.
> See details athttp://www.wescottdesign.com/actfes/actfes.html

That pattern "ignoring" scheme is what they call anti-sparkle logic.

http://inst.eecs.berkeley.edu/~ee247/fa04/fa04/lectures/L19_f04.pdf

This paper has a thermometer decoder towards the end. I'm not sure if
anyone ever published their anti-sparkle logic, but it's not that hard
to come up with a few schemes. Then again, many people don't know the
inside of a logic gate these days. ;-)

Flash converters are notorious for being difficult to drive. A flash
converter with the buffer on on-board is worth the money if the specs
include the buffer in the testing.

Thank you for each of your replies. What I am really after is
the priority encoder at the end of the flash ADC, which
generates the bits - I would like to verify the Boolean
equations for these.



On Mar 31, 9:59 pm, "m...@sushi.com" <m...@sushi.com> wrote:
> On Mar 30, 9:16 am, Tim Wescott <t...@seemywebsite.com> wrote:
>
>
>
> > On 03/29/2011 11:54 PM, Daku wrote:
>
> > > Could some DSP or electronics guru please direct me ? I am trying to
> > > get hold of a typical (some standard number of resolution bits)  flash
> > > ADC encoder logic equations.  Any hints, pointers would be very
> > > valuable. Thanks in advance for your help.
>
> > There may be some tricks, but basically a flash encoder with N bits has
> > 2^N - 1 comparators, that will go off in a pattern of
> > [[M ones] [2^N - M - 1 zeros]].  The logic is just a matter of
> > accurately counting to M, probably while also ignoring patterns that go
> > [1 1 ... 1 1 0 1 0 0 ... 0 0] or similar.
>
> > Have you googled "flash ADC circuit" yet?
>
> > --
>
> > Tim Wescott
> > Wescott Design Serviceshttp://www.wescottdesign.com
>
> > Do you need to implement control loops in software?
> > "Applied Control Theory for Embedded Systems" was written for you.
> > See details athttp://www.wescottdesign.com/actfes/actfes.html
>
> That pattern "ignoring" scheme is what they call anti-sparkle logic.
>
> http://inst.eecs.berkeley.edu/~ee247/fa04/fa04/lectures/L19_f04.pdf
>
> This paper has a thermometer decoder towards the end. I'm not sure if
> anyone ever published their anti-sparkle logic, but it's not that hard
> to come up with a few schemes. Then again, many people don't know the
> inside of a logic gate these days. ;-)
>
> Flash converters are notorious for being difficult to drive. A flash
> converter with the buffer on on-board is worth the money if the specs
> include the buffer in the testing.

I pointed you to the circuit of a parallel priority encoder that can be extended in ripple-through stages. If that isn't fast enough, you can extend the basic design. Note that some of the complexity arises from the combination of gates to build wider ones. Replacing the gate combinations with individual wider gates will reveal the structure more clearly.

Jerry
-- 
Engineering is the art of making what you want from things you can get.

What do you call a digital potentiometer? A DAC with an external bipolar reference has been used for that.

Jerry
-- 
Engineering is the art of making what you want from things you can get.

Jerry Avins <jya@ieee.org> wrote:

> What do you call a digital potentiometer? A DAC with an external 
> bipolar reference has been used for that.

I have wondered about record level controls on digital recorders.
It seems to me that the better quality recorders use analog
(real potentiometers), where others use digitial controls
(up/down buttons, and a memory for the current setting).

It would seem that you could use a DAC, with the input as the
reference voltage, and so as a digital level control.  Otherwise,
you use a DAC as input to a voltage controlled amplifier.

Are the digital versions noisier?

-- glen