Sigma-Delta A/D

Marco wrote:
> "John Monro" <johnmonro@optusnet.com.au> wrote in message 
> news:43671713$0$25854$afc38c87@news.optusnet.com.au...
> 
>>Marco wrote:
>>
>>>>Marco,
>>>>I am afraid not.  While the input circuit is differential, the rest of a 
>>>>LVDS buffer is optimised for digital performance, and not for the 
>>>>characteristics we require in a good operational amplifier.
>>>>A LVDS buffer would make a worse integrator than the cheapest op. amp. so 
>>>>why bother?
>>>>
>>>>Regards,
>>>>John
>>>
>>>
>>>Hi John,
>>>sorry for my terrible scheme.
>>>
>>>Please watch the picture at the link:
>>>
>>>http://www.maxim-ic.com/images/appnotes/1870/A237Fig04.gif
>>>
>>>That should be more clear.
>>>
>>>I thought that I could replace the 1-bit dac using a LVCMOS25 out pin 
>>>(without dac because it is only 1 bit) and connecting it to the negative 
>>>input of LVDS25.
>>>
>>>What do you think about it?
>>>
>>>Is it possible?
>>>
>>>Many Thanks
>>>Marco
>>
>>Marco,
>>Unfortunately, the DAC output voltage needs to be very well defined and 
>>noise-free, even though it is derived from a one-bit value, and no digital 
>>output is able to achieve this.
>>
>>I don't think there is any chance of realising CD-quality (16-bit) audio 
>>by trying to make a digital chip perform any analog functions at all. 
>>Digital noise on the ground and supply lines for example make it a 
>>hopeless job at the quality level you want.
>>
>>If it is essential to use a single chip, you could investigate the Lattice 
>>Semiconductor programmable combined analog/digital chips.
>>
>>
>>Regards,
>>John
> 
> 
> 
> I understand... so a way to do it could be buying a analog devices ad7400 
> (isolated sigma delta modulator (1 bit out)) and building the digital filter 
> into the fpga to obtain 16 bit output data.
> 
> What do you think about it? 
> 
> 
Marko,
I see that other contributors have already answered your question, and I 
agree with their comments.  My guess is that you are undertaking this as 
a tecnhnical challenge. and are not expecting any particular economic or 
performance benefits.  Good luck with the project.

Regards,
John Monro