Re: [oc] ADC code source ???

[Lars Segerlund <lars.segerlund@comsys.se>]

Niclas Hedhman wrote:
> On Wednesday 22 January 2003 18:21, Dharmeshbhai PATEL wrote:
> 
>>Hi list,
>>
>>I'm searching a Analog to Digital converter (ADC) vhdl or verilog code
>>source. I'm also interrested by some documentation and also a
>>test-bench.
>>If anyone has something about please help me and let me know if there is
>>a web-site for this..... Thanks a lot in advance.
> 
> 
> If I understand the subject correctly (and I am awfully new to this and try 
> learning by answering questions) HDLs currently have no support for analog 
> circuitry, and FPGAs certainly does not have it.
> 
> That said however, you should be able to make ADC support on-chip with a 
> couple of external analog circuits to implement the ADC. There are numerous 
> ways to implement an ADC this way, switched capacitor, stepper and 
> integrating comes to my mind right now.
> Your requirement would determine the best choice.
> But you will need at least an op-amp or a comparator off-chip, and some 
> resistors. If you don't have a external Sample-Hold, you can also forget 
> about an integrating ADC.
> And considering the low-cost, small form factor of modern ADCs, I don't think 
> it is worthwhile bothering.
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> 

  Actually, you can use a delta sigma conversion, in which case you will 
get exelent linearity, with two resistors and a capacitor as the 
external components, this also has the advantade that you can avoid the 
external amplifier, you simply use the ttl ( cmos ) levels on an input 
pin as the tresholds instead of an external comparator, this way you 
loose <1 bit precition and get an added 'semi white' noise as a bonus, ( 
this is good ! )

  / Lars Segerlund.

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