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# Feedback Compensation

149 Threads found on edaboard.com: Feedback Compensation

## current mode buck convertor compensation

If you got the correct model, you can break the loop with current feedback loop closed. Then you got a bode diagram that push LC poles to the high frequency. You can series connect a resistor and a cap to form a zero. You also can obtain another zero by parallel connecting a cap with feedback resistor divider. With enough zero, you get the loop sta

## Generating the bias voltage of an op-amp

Why need LDO ? It doesn't make any sense to use LDO as bias boltage generator, as you know, LDO need large cap compensation. I think you mis-understood what the LDO is Bandgap, with an op-amp and feedback resistor divider will have a gain >1, so you can get any voltage by resistor divider ratio.

## How can i calculate the bias current in CMFB feeedback circuit ?

well depends a little bit - I would look at the whole thing as a two-stage opamp with miller compensation (forget about the nmos h-bridge and dthe common-mode-feedback-resistors) ... so now you have to solve the problem how to design a two-stage opamp - and you should think first about the point imo - where there nondominant pole in the left han

## why the active feedback amplifier has high bandwidth?

In the attached papar, Gilbert said: the AFA can provides accurate performance right up to its unity-gain frequency. Why? Does anyone has any idea about this? the model of the active feedback amplifier is shown in figure 3 of the attached paper. Thanks a lot! Jiwei

## Why is there a CBB capacitor in this bandgap reference?

Well, CCB creates feedback growing on the high frequencies. CCB together with CBB creates divider - it doesn't depend on frequency.

## What is the internal amplifers?

Maybe it means the internal opamp does't need big output current and the feedback is fixed so compensation condition is fixed too , so the design would be clear .

## Need documents about compensation for Bandgap vol. ref.

I designed a conventional Bandgap voltage reference. In the transiant analysis, the output voltage oscillates. I want to know how to analysis the feedback loop in the voltage reference circuit and how to do compensation for it. who can provide me some documents about how to do compensation for a Bandgap voltage reference. Thank you.

## Question about the current compensation of switch power

I use current feedback and the boost working at CCM needs current compensation, does the boost working at DCM needs too? The flyback working at DCM needs current compensation? Thanks ahead.

## help! an opamp with two stage(Ahjua compensation)

who can tell me why the simulation result is that as follows? It's closed loop opamp,with the ratio of cap being 2:1.I used two common mode feedback,cuz the opamp is two-stage.I use Ahjua compensation.The schemetic is as follows. The simulation is run several periods to make CM voltage stable .But the result wave is lousy,it has a lot of spurs bo

## Stability of feedback loop

fala, There is no feedback path shown, except for the local feedback around the individual stages U1, U2, U3. How does the output of the error amplifier affect the differential inputs at V1, V2 at U1, U2. Please complete the schematic to show the overall feedback path. In general, you must provide compensation so that (...)

You bet! For all kinds of negative feedback on Bode plot it's of open loop amp it's should prevent situation when simultaineously gain cross 0 dB and phase equal 180 or more then 180. Thus ever for closed loop configuration with strong negative feedback (unit gain) the circuit remain stable. The phase margin may be more that 90, it correspond stab

## OPamp and comparators' design

It is usually not same. Comparators can have internal positive feedback that can make faster switching and response time... and so on... Here is what you are interested in:

## Let's discuss this real-world opamp

It is indeed an interesing opamp. One thing I noticed here is the role of P2 and N3: they indeed form a positive feedback with Q8, R2, R3, N3 and R7 loop. With proper amount of this positive feedback, very high impedance at E and F nodes can be obtained which makes this opamp very high gain and also eases the pole-splitting compensation. (...)

## Help me with analyzing this opa?

Here are my findings: 1) M14~M19 are common-mode feedback for the first-stage of this two-stage amplifier. The second-stage of this OTA already has a global CMFB from 'Vcmfb' input pin, so the first-stage CMFB is a local loop. You need to pay some attention to this local loop stability though because I don't see compensation cap for this loop.

## what is the role of this two capacitance?

Here are some refs: google: differential op amp common mode feedback selected!

## what's the difference between amplifier and comparators

In the high speed system, @1: The comparator is generally multi-stage to increase the gain and enhance the resolution . The amplifier is single or two stage to easy the compensation. @2: The comparator is not needed to be compensation, but the amplifier is needed. @3: The positive feedback is used in comparator to increase the (...)

## what is this capacitor used for in this bandgap circuit

1. startup cap. 2. it must be compensation cap of the feedback loop.

## Can I use the feedback capacitor as the compensation cap in this integrator?

Yes! The feedback response fives you +90 degree up to the frequency where the input cap of the diff inputs and the resistor set the pole. So the phase margin of the open loop increases. So look for a resistor which gives with the input cap a higher pole than the second/third parasitic pole within the opamp.

## application of unstable amplifer

if noise is white, then it will "inspire" ur system to "oscillate" at the PM=0, (positive feedback configuration).

## Whats the zero compensation effect and theory?

usually adding a zero in order to increase the phase margin of feedback system.