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Analog to Digital Converted (ADC) & Spartan 3

Greetings, I am looking at an application that will provide an analog input signal in the 125 to 500 KHz frequency range, and wanted to convert it to a digital signal that would be processed by a Spartan 3 FPGA. I found two xilinx app notes that address issues related these areas (but based on Virtex FPGA):

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(Virtex ADC)
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(Virtex Delta-Sigma DAC)

My other hardware requirements are low power (nanoWatt). I am wondering if you can help me in the following areas:

  1. Is it possible to achieve these goals given the requirements (125-500 KHz input signal, low power consumption, Spartan 3)? Note: The input frequency cycles at 125 KHz. Thus my thought is if I can devise a circuit that perhaps operates at 500 KHz, that is sufficient tolerance to assume that within the 500 KHz range the 125 KHz can be assumed to be slowly changing or linear.

  1. My thought is that it is possible to implement these using Spartan

3, but the cited links were to Virtex architecture. What concerns come to mind for the transition?

  1. Reasonable expectations about the resolution/accuracy of such sampled analog signals?

(a) For example, I am only able to discretize the analog input signal into an 8 or 10 bit resolution (meaning that 2^8 is 256 output values for the vertical axis, thus it is an expectation for the measure of round-off errors).

(b) Eventhough the Spartan 3 can run at 50 MHz, the ADC would only be able to sample slowly changing signals (

Reply to
Herb T
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The app notes are not limited to Virtex. You can use the same ideas on Spartan-3. What do you mean by nano-watt? The Spartan-3 consumes many milliwatts... Peter Alfke, Xilinx Applications

Reply to
Peter Alfke

nanoWatt is a term that was used by microchip, and has the following specification:

Low-Power Features: =B7 Standby Current:

- 1 nA @ 2.0V, typical =B7 Operating Current:

- 8.5=B5A @ 32 kHz, 2.0V, typical

- 100=B5A @ 1 MHz, 2.0V, typical =B7 Watchdog Timer Current:

- 1=B5A @ 2.0V, typical

See also

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Thanks,

-Herbie

Reply to
Herb T

signal

You're probably much better off just buying an ADC capable of sampling at whatever frequency you want, and connecting it to your FPGA through the converter's interface. You'll get much better performance and you won't have to do tricks to make the FPGA do something a standalone part will do much better and for less money.

-a

Reply to
Andy Peters

As far as the Spartan-3 power requirements, that is fine as I am designing with this part already. The part cited in the xilinx tech notes suggested 24 mA LVTTL output buffer and a comparator. I was hoping to devise the external circuitry that had requirements in the nanoWatt range. (See also other post for description of nanoWatt). Thanks,

-Herbie

Reply to
Herb T

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