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Design >> Analog Design >> Low Noise 8 Bit DAC
https://designers-guide.org/forum/YaBB.pl?num=1324532547

Message started by analog_design on Dec 21^st, 2011, 9:42pm

Title: Low Noise 8 Bit DAC
Post by analog_design on Dec 21^st, 2011, 9:42pm

Hi Guys,

I need to design Very low noise 8 bit DAC which should have integrated noise less than 50 uV. It is voltage DAC with 1 MHz BW. I do not want to use Current steering topology which will again need I/V Amp which would add more noise.

Please, suggest me architecture.

Thank You & Take Care

Title: Re: Low Noise 8 Bit DAC
Post by raja.cedt on Dec 21^st, 2011, 11:17pm

hello,
are you sure? because the moment you say 8 bit integrated noise will be fixed.

Thanks,
raj.

Title: Re: Low Noise 8 Bit DAC
Post by raja.cedt on Dec 22^nd, 2011, 1:52am

in fact capacitor charger based dac is voltage dac, but finally you need an opamp i guess otherwise you need to find some thing to buffer it out.

Title: Re: Low Noise 8 Bit DAC
Post by loose-electron on Dec 22^nd, 2011, 4:03am

your quantization noise at 8 bit and 1 V full scale amplitude
is bigger than your noise specifiied. Does not make sense.

Title: Re: Low Noise 8 Bit DAC
Post by RobG on Dec 22^nd, 2011, 11:12am

loose-electron wrote on Dec 22^nd, 2011, 4:03am:

your quantization noise at 8 bit and 1 V full scale amplitude
is bigger than your noise specifiied. Does not make sense.

I'm guessing it is a reference bias with trim to manage for process and DES^* corners.

Integrated noise is going to be limited by how much filtering you can have, so I think the best approach would be the simplest: an 8 bit tapped resistor dividing down a reference voltage and feeding an RC low pass filter.

^*Design Engineer Skill

Title: Re: Low Noise 8 Bit DAC
Post by Lex on Dec 23^rd, 2011, 12:17am

loose-electron wrote on Dec 22^nd, 2011, 4:03am:

your quantization noise at 8 bit and 1 V full scale amplitude
is bigger than your noise specifiied. Does not make sense.

Sure it makes sense. If it is a DC setting, you won't have quantization noise. ;) I would suggest placing a large capacitance at the output.

Title: Re: Low Noise 8 Bit DAC
Post by raja.cedt on Dec 24^th, 2011, 4:01pm

hello lex,
what do you mean by dc setting?

thanks,
raj.

Title: Re: Low Noise 8 Bit DAC
Post by loose-electron on Dec 25^th, 2011, 4:07pm

"it is a voltage DAC with 1MHz BW"

That does not sound like an set and forget DAC...

Title: Re: Low Noise 8 Bit DAC
Post by ywguo on Dec 25^th, 2011, 5:30pm

I like RobG's solution. Easy to implement. -- Yawei

Title: Re: Low Noise 8 Bit DAC
Post by RobG on Dec 25^th, 2011, 8:48pm

loose-electron wrote on Dec 25^th, 2011, 4:07pm:

"it is a voltage DAC with 1MHz BW"

That does not sound like an set and forget DAC...

Yeah I missed that, but I think the solution is the same. Integrated noise power is kT/C = (50uV)^2, so the only thing left to determine is the R for the filter. I get 1.6pF for the cap and 96k for the resistor at room temp, but would use as large a cap as I could afford and lower the resistance accordingly.

rg

Title: Re: Low Noise 8 Bit DAC
Post by loose-electron on Dec 26^th, 2011, 12:53pm

No follow up from the OP, so no clarification on what they wanted.