ADS1256 from TI has eight single-ended 24bit channels with high-impedance input buffer and PGA. OpenEXG project has PIC code to interface it (they use two channel version ADS1255, but it should be the same).
If you want differential inputs, then there is ADS1298, with 8 channels, PGAs and A/Ds, internal reference, plus ECG/EEG circuitry which you can ignore. I am not sure you can find any example code for this one, though.
If you are looking for resolution, then precise, low noise reference is a must.
I don't know what you mean by "UWB" (use standard or common abbreviations, no I'm not going to look it up, it's your job to explain), but many many micros have 10 bit A/Ds and SPI hardware. Even without the SPI hardware, SPI is simple to do in firmware by controlling the I/O lines directly.
In the Microchip line, there is a wide spectrum that meet these requirements. A low end PIC 16 can be small, cheap, and very low power. A fast dsPIC33 can run up to 40 MIPS but of course will use more power. There are various PIC 18 and PIC 24 in between.
What you need to explain is how fast you need to sample the 10 bit A/D and what the micro needs to do to these 10 bit values before passing them on via SPI.
This "answer" is more of a comment because too much important information is lacking. It can be turned into a answer if you cooperate and answer the specific questions asked, not what you feel like answering or or you think is important. As it stands, this question is too vague to be reasonably answered and should be closed. People will come by and close it as they encounter it. When 5 close votes are cast, it's over. The clock is ticking. You may have only minutes to a few hours. Do what I said exactly as I said quickly and you may get your answer. Ignore it and not cooperate and you'll be sent home without a cookie.
Added:
You have now added that the A/D sample rate is 500 kHz and that this raw A/D data is to be passed on via SPI. Since the A/D is 10 bits, this is apparently where you got the 5 Mb/s SPI data requirement from.
This is doable, but will require a reasonably high end micro. The limiting factor is the 10 bit A/D at 500 kHz sample rate. That's quite fast for a micro, so that limits the available options. Another thing to consider is that there is more to SPI than just sending the bits. Bytes may need to be transferred in chunks with chip select asserted and de-asserted per chunk. For example, how will this 10 bit data be packed into 8 bit bytes, or will it at all?
The main operating loop of the firmware will be quite simple. You probably set up the A/D to do automatic periodic conversions and interrupt every 2µs with a new value. Now you've got most of 2µs to send it out the SPI. If the device really can just accept a stream of bits, then it might be easier to do the SPI in firmware. Most SPI hardware wants to send 8 or 16 bits at a time. You'd have to buffer bits and send a 16 bit word 5 out of every 8 interrupts. It might be easier to just send 10 bits each interrupt in firmware.
Sending SPI bits in firmware if you only need to control clock and data out is pretty easy. Per bit, you have to:
- Write bit value to data line.
- Raise clock
- Lower clock
It would make sense to unroll this loop with preprocessor logic or something. A PIC 24H can run at up to 40 MIPS, so you have 80 instructions per interrupt. Obviously you can't use 8 instructions to send each bit. If you can do it in 6 it should work. There is some overhead to get into and out of each interrupt, so you might make the whole thing a polling loop waiting for the A/D, but then the processor can't do anything else. I'd probably try to cram this into the A/D interrupt routine using every possible trick so that at least a few forground cycles are left over for background tasks like knowing when to stop, etc.
Check out the Microchip PIC 24H line. I think most if not all have A/Ds that can do 500 kbit/s, and they can all run at least up to 40 MIPS. The new E series is even faster, but I'm not sure how real that is yet.
Best Answer
This isn't quite an answer, but rather an anecdote.
High-bit ADC are quite the nifty thing. Great resolution, along with high dynamic range, take away many signal-chain concerns.
I built a system for biopotentials with a 32-bit chip. Signal quality was excellent, as all my calculations told me they would be, with only some minimal amplification and anti-alias filtering. That said, my data was riding on what seemed to be an *enormous" square wave that I didn't notice during my prototyping. It had me quite baffled for a while.
Working backward, though, I figured out that the magnitude of the square wave was truly tiny.
Eventually, I had the box where this thing lived open, and I noticed serendipitously that when the programmer on microcontroller dev board that I was using wasn't USB-enumerated, that an LED flashed perfectly in time to my mystery square wave. That was making something sag, in the microvolt range, that was just huge in my 32-bit signal. It wasn't present during prototyping, because my on-board programmer was enumerated! Those bastards!!!!! The problem was resolved by removing the current-limiting resistor on the LED.
Why was this frustrating? Well, for the first time in my life, I didn't amplify enough for me to actually see the signals I was working with on an oscilloscope!!! I didn't do it, because I didn't have to.
I suppose the point is that selecting a 32-bit ADC created a funny opacity in my signal chain that I had to learn about the hard way. This was much like my early experiences with microcontrollers, where you can't just peek inside and know what's happening.
Long story short, high-bit ADCs are a valuable tool that makes analog design a breeze. That said, they're a tool, like any other, and the learning curve can be a challenge. Fortunately, in my case, I managed to ID my issue. I can tell you, I was under some real time pressure, working under subcontract to a medical device company. I was under pretty substantial stress for a few days, until I found my problem. There's a time and a place to start using new tools, and a time and a place for the tried and true.