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spectrum assistant doubt

Hi,

I'm designing a second order DT sigma delta modulator and im using the spectrum assistant to calculate the ENOB.

The values of the circuit are:

VREFN=350m

VREFP=1.45v

so, VREF=1.1V (vcm=900mV)

The circuit is differential and the amplitude of the differential input signal is: 990mV. At the output, im getting the bits stream and im using the spectrum assistant to calculate the parameters. the results are:

ENOB=16.22, SINAD=90.74, and the magnitude of the DFT signal is 810mV.

I'm using the hanning window and i set the peak saturation level to 1.1.

The issue is that i'm comparing the results with the formula of ENOB:

ENOB=(SINAD-1.76+20log((fullscale amplitude)/(Input Amplitude))/6.02

so, i replaced fullscale amplitude=1.1, input amplitude=810mV and SINAD=90.74 and i obtained ENOB=15.24

I only obtained ENOB=16.22 if i calculate like the fullscale amplitud is the double:

ENOB=(SINAD-1.76+20log((2*fullscale amplitude)/(Input Amplitude))/6.02

Can anyone could tell me if i'm not using the rigth formula or it happened before?

PD: I'm using IC615

Thanks in advance

Jorge

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Andrew Beckett over 12 years ago

Jorge,
Please log this as a Case with customer support. Whilst others may be able to help you, I'm not going to have much spare time over the next week to check an example and research this, so customer support is the right avenue.
Regards,
Andrew.
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Andrew Beckett over 12 years ago

Jorge,
Please log this as a Case with customer support. Whilst others may be able to help you, I'm not going to have much spare time over the next week to check an example and research this, so customer support is the right avenue.
Regards,
Andrew.
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