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58 Threads found on Cmfb Simulation
Hi All, I'm still on TT polyphase filter with current input and I saw a strange behavior in this structure when I'd simulated the CP1. My Opamp is a classical 2 stages with a cmfb on activ load. In Open loop the gain is 58dB for a UGF at 27MHz and Phase margin is 45 degree. The stange behavior is the following: In the global strucure, when
... second question was : what is the real gain of main amp? with cmfb or without it? With cmfb of course, as both circuits have to cooperate in reality (in practice). do we have to put the main or cmfb in unity-gain config? Of course not,
Additionally, if you do a time domain simulation and apply a common mode step up down to the input of your amplifier, you can monitor to see if your stable if no ringing occurs. Additionally, it might be interesting to see how well your cmfb regulates to your common mode level, AKA offset. JGK
Hi,everyone I've got some questions about cmfb stability in two-stage op amplifier. 1) Figure 1 is a schematic of two-stage opa with continuous cmfb circuit. I insert a device of iprobe (in analogLib library) to simulate the loop gain and phase of cmfb circuit. Figure 2 shows a voltage buffer using the two-stage opa. As we (...)
hello friends I have designed the folded cascode opamp...(fully-differential)....i have added SC-cmfb circuit to Amplifier ....but i am getting problem in simulating with PSS and PAC analysis.. my detailed steps for the analysis are as follows... set pss simulation for clock of 2.56MHz and input signal of 256K
when I do cm stb simulation in three_stage OP,I add L=500p to power and ground. the result shows that a peak in f=9.6G. If I delete L in power and ground,there in no peak in cm stb result. Why? please help me. thanks!
i have designed a two stage fully differential opamp with hybrid ahuja compensation (that is, two compensation capacitor used in the two cascode nodes of each branch), the first stage is folded cascode, the second is common source, and the cmfb is continuous common mode feedback which have two input pairs, one pair connected to vcm, the other pair
Hi, all Somebody in this forum said that, the OTA with S/C cmfb simulation could be done by PSS, PAC...., with spectreRF, but could anyone explain the detailed procedue or just give me some documents on that? I need it badly now! thanks a lot, and best regards Added after 5 hours 17 minutes: I tried t
Yes you can still use loopgain simulation methodology in cadence. However before running "stb" analysis you have to run transients till your CM is settled. An easier way is to use ideal cmfb circuit and then do can skip the transient analysis part. My answer assumes you already have good background simulation experience in spectre. Let me (...)
the output voltage is digital signal how could I do ? the cmfb circuit is designed with sc circuits I'm afraid that ac analysis couldn't carry out I perform pss and pac ,however the circuits doesn't converge when pss simulation general idea for psrr simulation can be : put a ac source in supply vsupply
I have same problem. I have designed amplifier which in AC simulation with ideal cmfb (using system from several VCVS) achieves about 75dB gain. Using PSS and PAC with real SC cmfb I achieve about 33dB. It is strange that in spectre.out file for DC levels for OUTP and OUTN are about 300mV output N cascodes are in triode region, but if I plot (...)
Hello, I have designed a fully differential folded cascode OTA with SC-cmfb. I haver tested the circuit using a SC-cmfb network using Verilog-A macromodel switches. And the OTA seems to work very well. When I replace the switches with transistors the clock injection is so bad that the cmfb voltage never is mantained at a fixed value (...)
hi, i'm confused by a problem like this: i design a fully 2-stage opamp with continue cmfb. and the ac analysis show dc gain is 90db ,also have go0d phase response. but after post-simulation ,the gain is only 50db! and To make things worse, the phase have Obvious Curved-up before the gain to 0db ! my opamp layout is almostly Symmetrical. and have
HI, anybody has some good ideas to simulate the AC characteristics of the differential opamp with switched capacitor cmfb circuit? Because the switched capacitor has no DC operating point, so how to deal with it in AC analysis? thanks.
Hi I`m desing a rail to rail folded cascode Op amp I have some question in Fully diff Amp 1: How to modeling the ideal SC cmfb Now I using the resistor and capacitor cmfb 2: How to simulation the Fully diff amp ICMR , SR Textbook(allen) describe thd single ended amp
when we perform simulation on fully differential op amps in close loop configuration,do we need to add cmfb circuit? or how to simulate fully differential op amps in close loop configuration? please help me out, many thanks!
Can anyone tell me the procedure or show me the link/tutorial......etc about SC-cmfb simulation? How to simulate common mode Loop gain and phase margin of the ota with SC-cmfb? thanks in advance.
OK, I think that you already have the answer: Because output impedance is high and there is not cmfb, output dc voltage goes near VDD. And, the AC simulation result is wrong. You need cmfb! If you don't have it implemented yet or it is not continuous time, then you need an ideal one. You have to create one block that fixes the
Does anybody know how to do the AC simulation for fully-differential OTA with sc-cmfb? This is what I have heard: 1) use vcvs to model the sc-cmfb; however, what should I put the gain for the vcvs? A very large value? Please look at the attachment for the schematic. 2) Use the pac (in spectre) Thanks a lot.
Hi friends, I am starting to design a folded-cascode fully differential amplifier OTA with cmfb. I am confused and don't know how to start because of the large number of mosfets. I know that the ideal flow is to start with hand analysis then move to the simulation stage, but I have two problems with hand-analysis, first is the