Problem on sigma-delta modulator design

[shaq]

The modulator is used for an application with the following specs:

(1) BW=24KHz
(2) OSR=128
(3) SNDR ≥105dB (1KHz input)
(4) Vdd=3v
(5) Analog common-mode voltage is Vcm=1.5V
(6) Vref=0.7V, ||u||max= ||v||max=0.9Vref
(7) TSMC 0.35um process

How to find the following items?

(1) Minimum capacitor size of the input stage
(2) Minimum CMOS switch size of the input stage with L=0.35um. (Need to run SPICE)
(3) If an opamp structure of two-stage, folded-cascode with PMOS input devices is used, find the key parameters of such opamp.
(4) Allocate a reasonable noise budget for this modulator and compare the quantity of modulator quantization noise and circuit thermal noise.



Thanks for your help!!!!!

 

[swicap]

I think u may find answers in wooley and rabii's book.

 

[mists]

it is very hard to get 105db sndr with one bit two-order 128 oversampling ratio modulator.

 

[swicap]

yes, i also think it very difficult.

it is very hard to get 105db sndr with one bit two-order 128 oversampling ratio modulator.

 

[willyboy19]

You probably need higher order modulator or multi-bit structure to get 105dB SNR at OSR=128.

 

[eldo]

Firstly, you should check your modulator topology if 105dB SNR is reachable by a second order SDM at 128 OSR.
Secondly, with Vref=0.7V, you need a very large sampling cap to reach 105dB SNR. Pay attention to KT/C noise and the thermal noise of the first OTA.

 

[shaq]

Can anyone tell me the procedure of calculating these parameters of opamp ?


Thanks so much!!!!

 

[xzcv]

if you wnat to get sndr 105db , you should be use 4-order modulator
you can reference
high-speed high-resolution dac ,1999,march,falakshahi

 

[gingerjiang]

Top-Down Design of High-Performance Sigma-Delta Modulators
by Fernando Medeiro, Belén Pérez-Verdú, Angel Rodríguez-Vázquez
you can refer to chapter 3 for the calculation of opamp's parameters.

 

[Btrend]

There is a comparasion table in the link below which show properties of commercial available SDM ADC
**broken link removed**

Added after 36 minutes:

u can also refer to this
**broken link removed**