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93 Threads found on Stage Cmfb
I am designing a 2 stage fully differential op-amps shown in the schematic: 118256 The resulting Bode Plots are shown here (magnitude and phase of vo_2_r - vo_2_l): 118257 My question is about the stability analysis, what should i do regarding the cmfb circuit, i heard about the iprobe com
I am building a 2 stage op-amp similar to that in the thread referenced. Mu question is about the cmfb, the solution in that thread is implemented using IDEAL voltage controlled voltage source, now if i want to realize it on transistor level, what should i do? or should i implement anoth
The common mode gain of an amp stage across frequencies depends on the ugb of the cmfb loop of that stage. In two stage amps, the differential loop forms a positive feed back for common mode signals. Hence it is essential to ensure that the common mode gain of your open loop amp is less than one across frequencies, which (...)
Hi, what are poles and zeroes in a compensation network like Type-3 compensation for 2 stage cmfb amp. how we can boost phase margin without affecting Bandwidth. by using miller compensation cap, BW decreases. thanks Safiya
I have designed 5MHz bw 2stage cmfb diff amp. but i could not adjust the Phase Margin using R,C values for the compensation, in my case when i achive PM = 60 , bw reduces to 800kHz. is there any method to compensate this amp of BW 5M or 3MHz with enough PM. Regards, Safiya
Hi guys, I want to design a full-differential two-stage OPA. The first stage is telescope cascode structure and the second on is usual common source structure. I want to use switched-capacitor cmfb to make the output common-mode voltage stable. I am wondering now that how many SC-cmfbs I should add in the OPA. One (...)
This is a simple two stage OTA ... with fully differential output at first stage and single ended at the second stage. Gain will be approx gm^2 (ro || ro)^2 .. assuming the all the ro and gms are same. The MOS arm connected to VB2 is used for cmfb (Common Mode Feedback) as the first stage is fully (...)
I think the circuit already has a cmfb around the first stage as mentioned in the text. For the 2nd and 3rd stages they don't need cmfb because they are self-biased and not supplied by current sources from both top and bottom. This is assuming good matching of the current mirrors between the 2nd and 3rd stages.
Fully differential opAmps always need a cmfb. Here, the cmfb stage is already integrated: M41 - M46 . The common mode feedback works from M46 into M36 , whereas M43 to M34 as well as M44 to M33 provide positive 1/N feedback to the output stage.
Hello everyone, I'd'like to design a switched capacitor amplifier 94797, But I don't know how does this amplifer work. Here is my own point of view: in the S1 phase, the circuit in the sampling phase, VCM and LM49 supply a cmfb; in the S2 phase , the circuit is amplified stage. However when I use the spectre simulation
You might be able to get a common mode of Vdd/2 by appropriate sizing and also using cmfb. You cannot fix the common mode without using cmfb otherwise it would vary with corners. Another option is to have a second stage. It would be easy to use cmfb to get Vdd/2.
I am designing a 2 stage Miller compensated OTA. I have problem in fixing the output common mode voltage. There was no problem when i designed a differential output OTA, as a cmfb loop ensured proper output DC voltage. But when i tried to design a single ended OTA, i dont get the desired common mode voltage. The first stage common mode (...)
Hi, I was wondering how the polarity of your cmfb works. I am assuming you are just sensing with resistors. If you sense the output of the second stage and feed that back to the first stage then it would cause positive feedback. Consider the output CM voltage from the second stage lowers a bit. This means your feedback (...)
I am designing a 2 stage Class AB op-amp , with cmfb network, The OP-Amp will be used as an integrator (with Capacitive -ve feedback). But i have a question regarding the stability , GBW and PM calculations: I am not sure whether i need to check the stability and PM condition, 1) Using phase and gain of the differential output . With NO
but the first stage was not fixed ......why does this happen By nature of a two-stage amplifier. It's neither feasible nor useful to bias the first stage output to Vdd/2. The bias point of the first stage is commanded by Vth of the second stage transistors.
Hello, I'm drawing a 2 stage fully differential miller OTA with 2 cmfb networks. These cmfb networks are ideal and contain a vcvs with a gain "Acm". However, when I put 2 instances on my schematic and use the ADE (Analog Design Environment) to retrieve the variables I only get 1 variable Acm for the 2 blocks. I wish to control them (...)
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 (...)
Where did you get this strange amplifier topology? For reasonable gain and common mode range, I would expect p channel transistors in place of M1 and M2 and the output stage driven from the top (M10/M12) rather than from the bottom (M5/M6).
Hi, this topic was discussed before, it did show 5 threads when i typed the tilte. here is one i almost used the same cmfb scheme as the last post for the class AB output stage, that is tuning the PMOS gate by adjusting the current into the output nodes. check the picture below 8131
I think this is a good question. C2 directly loads the output stage all the time, while C1+C2 loads at half clock cycle. for faster settling time to arrive ideal Vcm, C1 has to be larger than C2, right? did k.martin tell the reason why c2 should be approx. 10 times of C1?