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Design >> Analog Design >> Full scale voltage of a delta sigma modulator
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Message started by saralandry on Jun 20^th, 2020, 6:04pm

Title: Full scale voltage of a delta sigma modulator
Post by saralandry on Jun 20^th, 2020, 6:04pm

Hi,

I have a question related to a delta sigma modulator. What does determine the full scale of a delta sigma modulator. Is it the reference voltage of the quantizer or it is the reference voltage of the feedback DAC in the delta sigma modulator. For example if the supply voltage of the modulator was 1.8-V and the reference voltage of the DAC is 1.5V, would that mean the full scale of the modulator is 1.5-V?

If my supply voltage is 1.8-V, how should I set the reference voltage of the quantizer and the reference voltage of the feedback DAC to be able to apply an pseudo differential input of 1.8-V?

I am a bit confused and it will be highly appreciated if someone elaborate it.

Title: Re: Full scale voltage of a delta sigma modulator
Post by Tako on Jul 2^nd, 2020, 4:30am

Full scale like with normal ADCs? It depends on your voltage limit that you may "transfer" properly. Usually equal to VDA (analog power supply or either power supply) or less.

For example what is the limit in 1-st order of delta sigma ADC (see attachment - source https://payhip.com/b/kO4T paid version).
In that case is the reference voltage V_REF.

Title: Re: Full scale voltage of a delta sigma modulator
Post by saralandry on Jul 3^rd, 2020, 7:56am

Thanks Tako.

So, if I'v understood correctly,

1- for a single-ended delta sigma, if we want to have an input full scale of e.g. VFS we need to set the reference voltage of the feedback DAC to two times of the VFS (i.e. Vrefn=0 and Vrefp= 2*VFS)

For a fully differential delta sigma, if want to have an input full scale of VFS, we need to set the reference voltage of the DAC to VFS (i.e. Vrefn=0 and Vrefp=VFS).

Am I right?

Title: Re: Full scale voltage of a delta sigma modulator
Post by Rakesh on Oct 7^th, 2020, 8:26pm

It depends on the Maximum stable amplitude (MSA) of your DSM. typically with single bit DSM MSA is about 60-70%