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14 Threads found on edaboard.com: Cmfb Capacitors
how are you measuring your DC gain? at what frequency are you clocking your cmfb? can you show us a transient plot of how the cmfb is settling?
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
I think if you are using the two stage amplification in the cmfb amplifier, the same problem of two stage Opamp stability problems are appearing in your circuit. May be your test bench could be missing some capacitances required. Connecting the two differential outputs with two identical capacitors to the cmfb node may solve the problem 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
To simulate in ac, you can use two resistors (1Gohm at least) connected to the output(assumed differential outputs) and two capacitors in parallel with the resistors. Then connect the other end to a VCVS, where the gain of this VCVS is the loop gain of your cmfb circuit, output of the VCVS connect to the transistor where you can to feedback example
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
For cmfb, we usually choose the capacitors Ccm such that the bandwidth of the cmfb is more than half of that of the amplifier. 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
If your application is switched capacitor, use a discrete cmfb because, it saves power and do not have stability problems in the cmfb network. In same cases you also reduce area, by using small capacitors. However discrete time or continuous time, both work in high gain amplifiers. I have used both for 110 dB DC gain. Bastos