Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

PAC and PSTB for switched capacitor integrator

Status
Not open for further replies.

venn_ng

Member level 5
Joined
Mar 26, 2017
Messages
87
Helped
1
Reputation
2
Reaction score
1
Trophy points
18
Activity points
645
I am designing a traditional 1st order delta sigma modulator. I tried to find the input referred noise of the integrator and switching network (circuit is shown). I set vin+ = vin- =vcm & then I set v to be a square wave at a frequency fclk/2 (to emulate the limit cycle behavior of first-order delta sigma for code 0). This is my periodic steady state point. I am also using a differential stb probe as shown to simulate pstb.

First question, is this how you simulate pss for switched cap integrator (note that this is not a switched cap amplifier but an integrator).

I apply PNOISE on this and find the output referred noise (at the output of differential integrator) & scale back to the input by using the PAC gain function by specifying the output and input nodes. I also tried using the input referred noise function in PNOISE. The results don't make sense, as the numbers are way off.

And for pstb, I see that the DC loop gain of PSTB starts off at 0 (i mean -∞ dB) and goes up at 20 dB/decade. Is this due to the integrator action? Is this how do you stability of an integrator using PSTB.

I read articles on simulating PSS/PSTB/PAC for switched cap amplifier but for integrator I am not sure if this is the right way to do. designer_guide1.PNG
 

I think your schematic ought to include some amount of resistance at each incoming voltage. And for good measure put a resistance in series with capacitors. Otherwise the simulator is unable to calculate an RÇ time constant. The result tends to be spikes of high current as caps charge and discharge instantly, unlike real life.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top