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Design >> Analog Design >> Why dose SDM ADC has larger energy of IM5 and IM7
https://designers-guide.org/forum/YaBB.pl?num=1522464850

Message started by abbotvan on Mar 30^th, 2018, 7:54pm

Title: Why dose SDM ADC has larger energy of IM5 and IM7
Post by abbotvan on Mar 30^th, 2018, 7:54pm

My design is 2nd order/104 OSR/5 level quantizer sigma delta ADC.
Simulation of 2 tone shows distortions, and the energy of IM7 is larger than IM5, meanwhile, the energy of IM5 is larger than IM3.
Also, there is lM2 and IM2 energy is 6dB less than IM3.
For other circuits, such as opamp, the max energy should be IM3.
I wander which kind of non-ideality can cause larger IM5 and IM7

Title: Re: Why dose SDM ADC has larger energy of IM5 and IM7
Post by abbotvan on Apr 2^nd, 2018, 10:48pm

updata
This SDM ADC has a DWA block after quantizer, if dwa enabled the IM2(F2-f1) is only 62.6dB, while dwa is disabled, IM2 is 80.5dB.
I've checked the function of dwa and it works right. Meanwhile, dwa indeed decreases the energy of IM3.

ordinary, IM2 is caused by asymmetry, why dwa can cause larger IM2 energy.