ali kotb
Member level 3
hello All ,
I have a problem of getting the PSD plot of 2nd order switched cap sigma delta
the opamps, switches are designed using veriloga.
the input is taken every 0.1s using a reset switch on the
integration cap (incremental ADC)
vref= +-0.5 , vin=+-.216 (DC input)
OSR = fs/2fo
fo = BW of DC signal = 10 Hz (taken every 0.1s)
OSR= 256 --> fclk=5.120 KHz
according to Schreier it's best to use hann window using N for FFT= 64*OSR = 2^14
so I ran my transient simulation from 0 seconds to 64*OSR/Fclk= 3.2 seconds ( it took me an hour simulation time)
and that is the curve I got (attached- zoomed and original)
I have 2 Question :
1. what is the reason of the peaks at every 10 Hz ?
2. the noise shaping is not equal to 40 as expected from 2nd order modulator
and is there is any comment on the way I do analysis ?
Regards,
I have a problem of getting the PSD plot of 2nd order switched cap sigma delta
the opamps, switches are designed using veriloga.
the input is taken every 0.1s using a reset switch on the
integration cap (incremental ADC)vref= +-0.5 , vin=+-.216 (DC input)
OSR = fs/2fo
fo = BW of DC signal = 10 Hz (taken every 0.1s)
OSR= 256 --> fclk=5.120 KHz
according to Schreier it's best to use hann window using N for FFT= 64*OSR = 2^14
so I ran my transient simulation from 0 seconds to 64*OSR/Fclk= 3.2 seconds ( it took me an hour simulation time)
and that is the curve I got (attached- zoomed and original)
I have 2 Question :
1. what is the reason of the peaks at every 10 Hz ?
2. the noise shaping is not equal to 40 as expected from 2nd order modulator
and is there is any comment on the way I do analysis ?
Regards,