2 nd order sigma delta ADC

[satyanitt]

my spec goes lyk this:
Continuos time sigma delta ADC
order=2
fb=24khz
osr=128
target bits=12
how shall my integrator spec should begin wid lyk UGB,gain, slew rate of the OTA in integrator? help me out plz

 

[jgk2004]

Well first what does LYK mean?

just for starters. I would say you need to investigate how your coefficients in your structure will react to finite UGB, gain and slew rate.

But for basics, you UGB should be 3 to 4 times you sampling frequency Fs. Your gain should be higher then your OSR, so 128, and your slew rate will be fine unless your UGB is lower then 3 to 4 due to other techniques of compensating for finite GBW within your loopfilter coefficients...

Hope this helps
Jgk

 

[satyanitt]

LYK means 'like'...sry to use it...
Do u hav any reference text to that support the UGB must be 3-4 times the Fs...thanks alot sir...

 

[jgk2004]

The reference supporting 3 to 4 times Fs is here.

Compensation of Finite Gain-Bandwidth Induced
Errors in Continuous-Time Sigma–Delta Modulators by Ortmanns

Unless you really get into the details of modelling and making the modulator tolerate smaller FGBW, then I would just stick to 3 to 4.

Hope this helps
Jgk

 

[satyanitt]

hai,
Its very useful suggestion and thanks alot...
But what can be the slew rate specification in particular for the first stage OTA and second stage OTA....for my first and second stage integrators.?
Iz it enough to take for UGB alone wid out slew rate....?
thank u

 

[jgk2004]

If you take the 3-4Xfs for UGB the slew rate is always met.

Jgk

 

[satyanitt]

thanks alot sir....