sigma delta ADC over-sampling rate trade-off.

[nathanee]

Hi,

There is a question about the sigma delta ADC over-sampling rate v.s. order number trade-off consideration.

Supposed that the target is to have SNDR=100dB, there are two solutions for the SD modulator.
1. OSR=512*fs and 2nd order.
2. OSR=256*fs and 3rd order.

If the opamp design is not the bottle-neck, that means opamp can meet slew-rate, BW requirements when OSR=512*fs.
The power and area are not the design concern.

Is it ok to use OSR=512, any systematic drawback?
The recent paper is targeted toward the lower sampling rate. I think one of the reason is low power, any other benefit?

Sorry for my poor English, hope you all can understand my question.
Regards,
-nathan

 

[devrimaksin]

There is notting wrong to chose OSR 512, but you dont need that GBW of the opamp is 512*fs
In most case 10*fs is more than enough

 

[terryssw]

Your question may be too ideal, and if you don't concern power, area, opamp speed, just increase your OSR to very large is ok or just increase your filter to very high order is ok? You don't need to consider speed, so why don't use very high OSR? you don't care about the power and area, so why don't you use high order?

Block level investigation is to search some topology that best meet the practical design specs such as power, area, speed, noise, etc. So you must consider these aspects before you choose what OSR and what order.