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14 Threads found on edaboard.com: Cmfb Capacitors
Hi all, I am designing a telescopic ota with SC-cmfb. These are my design specs: vdd=1.8V gbw=500MHz load=100fF DC gain>40db My design works well with an ideal cmfb. My problem is the design of the SC-cmfb. I read the paper of Choksi and also several books. Once i connect the SC-cmfb to my OTA, the DC gain drops. (...)
I'm aware of only your first suggestion, especially if it's a continous time circuit. Two resistors across the output will require a current if the differential output is nonzero, and, in an OTA, they will lower the voltage gain; therefore, they're typically taken as large as possible. The large R, combined with the input capacitance of the comm
hello everybody, i need to know the influence of the feed back capacitors in the scheme bellow on the outputs of the opamp. thank you for your help maalma
for a fully differential opamp, SC-cmfb is commonly used. if Gain-Boosted telescopic opamp is used, then both main opamp and auxiliary amplifier need SC-cmfb circuit. i want to ask: how to choose the value of the two cmfb capacitors C1 and C2 (assume C2 is cmfb capacitor) for both main opamp and auxiliary (...)
How can openloop GBW and closedloop GBW be the same? They are different by the factor β, which is the feedback factor. β=Cf/(Cs+Cf+Cin) Your equation to find Cl is right. We have to include all the capacitors loading the opamp which also includes cmfb capacitors as well. Also read the latest paper on pipelined ADC
hi, I try to design fully differential folded cascode amplifier, but have problems with cmfb stability (see attached circuit). There is too much phase shift in cmfb path (260 degrees!), but I not know where it is from!! And magnitude response of cmfb path is 80dB!! I think because of 40dB gain from cmfb amplifier, and (...)
I want to plot the I-V transfer characteristic of a class AB opamp; something like the should I do it? It's going to be used in a switched capacitor architecture and the output cmfb of the circuit is switched capacitor. So, should I add two capacitors in the output and plot t
We did common mode feedback for an opamp using a switched capacitor structure.. The structure is as shown below.. voutp and voutm are output terminals.. We are controlling one of the bias with this cmfb so that output node remains a constant.. Our opamp is 2
i have some questions about fully differential opamp,please give me some advice: 1\how to decide the value of two inputs and two outputs,a input to Vcm,the other to Vin,is that right? if so,what's the value of two outputs,and what's the value of Vocm? 2\if i use SC-cmfb,how to decide the value of the two capacitors? what's the timing of phi1 an
I designed a SC cmfb, but when I added this cmfb to an OTA, the gain of OTA would decrease seriously,even decrease to <0dB. Why? The current is too small(For my OTA, it's current is 350uA)? Or the cap of cmfb is too big(One is 150fF, and another is 800fF)? I have no idea about what happened. Anybody can explain? Thank you in advance!
hello, i want to do a cmfb for a simple OTA , do i have to use two resistance to sense the cmfb from the OTA , or is there another methode for CM sensing , also in cmfb do i have to compare to a certain refrence or is there another way? thnx and regards a.safwat
How to choose the values of the capacitor in SC cmfb circuit? Does the ratio of the two capacitors affect the time to get a stable value of Vcmfb?
A few points about your schematic, which you did not draw correctly: 1) CSH capacitors: they can not be connected at the first stage outputs to the second stage gate inputs. If you do so, the second stage would be floating and no DC bias; 2) The cmfb switches are not drawn correctly as well. You may refer to any books which descirbe this SC C
Hi Guys, I am designing a differential Opamp for my Pipelined ADC. Can anybody tell me should I use continuously or discrete cmfb circuit if both power dissipation and layout area are considered? Why? I also tried the continuously one (in Martin's book "analog integrated circuit design") with feedback to control the output stages bias curre