Questions about amplifier in 2nd order Sigma-Delta

[mitrobge]

cmrr pssr site:edaboard.com xf analysis

It is rapported that the unity-gqin frequency of the amplifier should be 3-4x the sampling frequency of the switched capacitors circuit.

1.What about the 3db frequency in an open loop configuration?

2.I use a SC circuit to control the CMFB.
Can you give some information about pss analysis (is xf also relevant?) and how to simulate the gain?

3.How can i simulate PSSR and CMMR with the SC CMFB circuit?

 

[Btrend]

It is rapported that the unity-gqin frequency of the amplifier should be 3-4x the sampling frequency of the switched capacitors circuit.

1.What about the 3db frequency in an open loop configuration?

2.I use a SC circuit to control the CMFB.
Can you give some information about pss analysis (is xf also relevant?) and how to simulate the gain?

3.How can i simulate PSSR and CMMR with the SC CMFB circuit?

1. unity-gain frequency (UGF)=Adc*β*ω_3db ==> ω_3db =UGF/(Adc*β)
3. PSRR: introduced AC noise at the VCC, closed SC loop and CMFB loop, then find gain of ΔVo.
CMRR: shorted Vip & Vin and then introduced AC noise at Vip+Vin, closed SC loop and CMFB loop, then find gain of ΔVo.

hopes this help u!

 

[ablue]

you can simulate the effect of opamp's bandwidth on the performance of system in behavior model, it also relate to the structure you used, 3-4*fsample usually not enough for high performance.

ablue