ADC chip

[Froskoy]

Hi,

I'm looking for a 48MHz ADC chip which can convert a +/- 5V analog signal into an 8 bit parallel signal which will then be fed into a microcontroller.

The reason I'm not doing the A/D conversion in the microcontroller is to increase speed.

I would like to run the A/D chip on the same clock as a 48MHz PIC.

I found the ADC-321, but this has a very limited voltage range.

Does anyone know of a suitable chip? It would really, really, really help me.

Many thanks,

Froskoy.

 

[crutschow]

Are you trying to sample the input at a 48M sample/sec rate? If so a 48MHz clock-rate PIC will not be able to read the data at that rate. That's a very fast data rate and needs a high speed DSP chip to handle it.

And where are you getting a +/-5V, ≈20MHz analog signal?

 

[Froskoy]

Hi,

Thanks very much for the reply.

The analog signal is from a laser scanner, profiling an object in detail, very quickly.

The PIC was going to read, store (in internal flash), read, store, read, store, etc. and then process the data when finished.

What do you reckon is the fastest speed I can get a 48MHz PIC to do this? Is there an ADC that will convert the analog signal at the fastest speed a PIC can realistically read the data (will be alternate clock cycles I guess - one for read - one for write - will the access time of the memory be longer than a clock cycle????)

I hadn't thought of a DSP - thanks very much for that suggestion. I'll research it - but would be very grateful if you could answer these questions as well.

Many thanks again,

Froskoy.

 

[Ubergeek63]

Hi,

Thanks very much for the reply.

The analog signal is from a laser scanner, profiling an object in detail, very quickly.

The PIC was going to read, store (in internal flash), read, store, read, store, etc. and then process the data when finished.

What do you reckon is the fastest speed I can get a 48MHz PIC to do this? Is there an ADC that will convert the analog signal at the fastest speed a PIC can realistically read the data (will be alternate clock cycles I guess - one for read - one for write - will the access time of the memory be longer than a clock cycle????)

I hadn't thought of a DSP - thanks very much for that suggestion. I'll research it - but would be very grateful if you could answer these questions as well.

Many thanks again,

Froskoy.

I am not really familiar with all the PICs ... 10MHz maybe - read (instruction fetch + read) write (instruction fetch + write) loop (instruction fetch + adjust counter + branch to start)

an ARM chip... LPC1751 memory (port byte) to memory DMA

Dan

 

[MrAl]

Hi,

Arent there some very fast PIC's out there these days? Like the 32 bit ones?

Anyway, a company called "Analog Devices" makes a lot of very fast ADC chips. I was looking into one more than ten years ago that worked up to 100MSPS with an 8 bit data output so today im sure they have even faster ones and cheaper too.

 

[Ubergeek63]

Hi,

Arent there some very fast PIC's out there these days? Like the 32 bit ones?

Anyway, a company called "Analog Devices" makes a lot of very fast ADC chips. I was looking into one more than ten years ago that worked up to 100MSPS with an 8 bit data output so today im sure they have even faster ones and cheaper too.

non of that matters without DMA you are looking at a 3-10 bus cycle loop

 

[crutschow]

The required minimum sample rate of the ADC is determined by the highest frequency component of the scanner signal. Do you know what that is?

Otherwise it would appear that you are just guessing at what you need.

 

[Ubergeek63]

The required minimum sample rate of the ADC is determined by the highest frequency component of the scanner signal. Do you know what that is?

Otherwise it would appear that you are just guessing at what you need.

if he is scanning an object he knows EXACTLY what frequency he needs - how long he wants to take to scan a line times how many pixels he wants to read in.

what he did not know was what was going to limit how fast he could do it.

 

[crutschow]

if he is scanning an object he knows EXACTLY what frequency he needs - how long he wants to take to scan a line times how many pixels he wants to read in.

what he did not know was what was going to limit how fast he could do it.

Certainly he should know. My question is, does he?

I question this because is seem unlikely that the system would generate a ±5V signal with upward of 20MHz frequency components that the 48MSPS sample rate would imply. Normally signal processing signals with that high a frequency are only a volt or so.

 

[Ubergeek63]

Certainly he should know. My question is, does he?

I question this because is seem unlikely that the system would generate a ±5V signal with upward of 20MHz frequency components that the 48MSPS sample rate would imply. Normally signal processing signals with that high a frequency are only a volt or so.

well that depends on if you are talking professional or hobbyist... many hobbyists don't know what the real world is like, hence I have to tell people over and over that the L297/298 motor chips are crap! and hobbyists do not care about emissions...

dan