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# spectrum assistant doubt

Last post Fri, Apr 12 2013 2:12 AM by Andrew Beckett. 1 replies.
 Started by jvdelacruz 10 Apr 2013 07:19 PM. Topic has 1 replies and 698 views
• #### Wed, Apr 10 2013 7:19 PM

• jvdelacruz
• Joined on Tue, Mar 19 2013
• Posts 1
• Points 20
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=350mVREFP=1.45vso, 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=15.24I 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 advanceJorge
• Post Points: 20
• #### Fri, Apr 12 2013 2:12 AM

Re: spectrum assistant doubt
 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.
• Post Points: 5