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# Amplifier Stability

225 Threads found on edaboard.com: Amplifier Stability

## Class AB Amplifier Help

The transient regime may blow the transistors by over-driving for short period. Or there might be a instability so the amplifier oscillates.Have you ever checked the stability of the closed-loop ?

## Slew-rate amplifier - overshoot

Compensation networks for small signal stability will impose a slew rate limitation, and uncompensated (or marginally stable) amps will overshoot (if not oscillate). Particularly in bipolar amps, if you "wind up" any of the stages into saturation or cutoff, the overshoot will be worse than when the loop remains linear. MOS amps can also show

## Circuit to boost the output current of an opamp, with large capacitors on the output?

I think that is a stability problem because there is feedback circuit from output to OPAMP and phase shift is not clear. As KlausST said, a AF Power amplifier can be used, they are stable.

## sine wave oscillator

If frequency stability is an objective, you'll use separate oscillator and power amplifier stages. Most 27 MHz power applications are required to use 27.12 MHz ISM band and keep the +/- 163 kHz bandwidth strictly. In addition, crystals are small signal devices and will be damaged by high voltage levels. Having high output voltage in a single st

## Stability of the CSA amplifier

The assumed first order gain characteristic isn't bad as an estimation. There's an additional cascode stage pole, but you can probably ignore it. The other expressions are however only right if C2 >> Cf, otherwise the amplifier output impedance matters. As a short cut, it's rather unlikely to drive an amplifier with a single gm stage into i

## Stability of the CSA amplifier

Hello Friends, I am designing a Charge sensitive amplifier and would like to study about the stability. we know, A/1+AB where AB is the open loop gain. If AB is equal to -1 then the system will oscillate. How would I know that AB will be equal -1. Please tell me the process to calculate. A= G sCdRf/ 1+sRf( Cd+Cf) B= 1+sRfCf/sRfCd... P

## what analysis I can do for amplier design project?

check the stability of the amplifier after design, do the matching stuff and then do s-parameter analysis and try to plot s21 and s11.

## Closed loop for accurate voltage measurement

The PMOSFET is wrongly connected in your schematic. You should also consider that the MOSFET booster circuit is adding gain and reducing phase margin so that the amplifier needs additional frequency compensation to achieve stability.

## wideband power amplifier matching

First I would check that your layout is appropriate, according to the manufacturer's recommendations. A little extra source inductance can have a large impact. You may need to add lossy elements to the amplifier to get wideband stability. This can be shunt resistance on the gate or drain to ground, or a series RC connected between the gate and dra

## Stability of the amplifier

K>1 simply means that the amplifier is stable at that given frequency regardless of its output and input reflection coefficients. That is, assuming your layout and bias conditions are identical to that under which K was derived. K<1 means that there exists the possibility of instability, if you choose certain input and output reflection coefficient

## circuit for extracting signal average

"go to an op-amp" and being "in the op-amp path" are different things. Rather mysterious how a low-pass in front of an amplifier should affect stability. May be you are not telling the full story? Averaging can be a achieved by low-passes or integrators, ín other words poles at low frequency or zero. Quite obvious, I think.

## Why do we need to check stability of open-loop OPAMP

Hello stability issue occurs only when there is a feedback in an amplifier. If an OPAMP works in open-loop, there isn't the stability problem. However, when we design an OPAMP, we consider the phase margin and gain margin although there isn't a feedback initially (we may include a feedback path after designing the amp). What is (...)

## Sources of AC elements in Feedback loop

For an error amplifier, the stability is defined based on the response of the amplifier for a range of sine wave frequencies. or something like that... stability can be determined by analyzing the loop gain magnitude and phase versus frequency. For simple cases, the phase margin can be used as stability (...)

## How to select control gains for dc-dc converter

Do you mean that you want Vout=2*Vin? Or that you want an {error amp to output} gain that ensures stability given the op amp frequency response, output filter and feedback network details? You want high enough loop gain that load regulation is decent and PSRR is driven down to amplifier-internal limits, but not so high that you haven't gone t

## CMFB circuit stability

Dear All, I have designed a fully differential operational amplifier with Continuous time common mode feedback circuit. Now I want to check if the CMFB circuit is stable or not. I already tested my operational amplifier in differential mode and it is stable using the AC analysis. Can anyone please tell me how can I test my CMFB circuit if it is

## determining the op-amp stability state

The original post is showing that a negative feedback loop with pure delay (your assumed step delay) but no bandwidth limitation won't be stable. Any real amplifier and respectively any feedback loop has however bandwidth limitations (poles in terms of linear system analysis). A loop ruled by a single dominant pole (the case of typical unity ga

## EM_Linear Vs Non_EM_Linear RF PA Stability Simulation

Hi all, I have designed an amplifier and stabilised the FET unconditionally and checked the K factor across wide band using AWR microwave office and PA was stable across the band. However, when I extracted the EM structures of the matching networks and checked the K factor again, I found out that K factor is below zero at som

## buffer amplifier - phase

to make analog amplifer, I connect negative feedback and phase shift of amplifier should be below 180 when amp gain is unity gain because if not, output of amp is larger more and more or oscillated. But when that conditions are satisfied, how can i prove that amplifier is not oscillated? for example, at specific frequency, when gain is 1400

## to find stability of RF amplifier

yes i am trying DC bias to my RF Power amplifier Real loss would u like to explain little bit

## Things to consider to design a SMPS for 500kHz RF Class D amplifier

The class d is almost certain to have some input capacitance with it..make sure you do your full bridge stability testing with this input capacitor in there taken account of aswell. You may find that your average power draw is much much less than your peak power draw. You may be able to cheat on your transformer winding thickness?s if the power d

## linearized unity gain amplifier

124453 124454 Figure 1 is a emitter-switched THA, and Figure 2 is used to replace the input amplifier in Figure 1 due to its better linearity according to the reference in the IEEE

## [moved] Linear regulator error amplifier input & output voltages & compensation type?

An opamp is frequently used as an error amplifier in a linear power supply. An opamp can have a DC and very low frequencies voltage gain from 90dB (thirty thousand times) to 130dB (millions).

## MC1648 how stable is it?

Hi, I consider the MC1648 as an oscillator in LC mode for HF CW transmitting. I would like to know to things: 1. What sort of output power and impedance should I expect out of it? (in order to see what will be the drive to the power amplifier) 2. What sort of frequency stability should I expect out of it? Is it enough for CW transmitting on HF am

## Current to voltage converter using op amp: Why the output voltage not same as equat?

The LT6200CS8-5 is designed to operate with a gain no lower than 5 for stability. It will likely be unstable in the first circuit you referenced, which has a voltage gain of 1. Gain of 5 in this specification is referring to the closed loop gain in non-inverting amplifier configuration, assuming a pure resistive feedback network.

## logarithmic detector amplifier - discrete

Obvious Video amplifier on Fig. 10 is what you want. It's output is 1V/20dB (~4Vmax). Discrete components does not enable simple realisation with good enough temperature stability. - - - Updated - - - Here you have more compact log detector with AD8703 with greater dinamic range:

## Replacing base resistors in RF amplifier

Problem you have is when resistors are changed Ic current must not be changed. Resistor 1k can have so high resistance that 270ohm resistor is not needed. In this case temperature stability is lowest possible. Changing resistors you also change the gain and phase of amplifier which may stop oscillating. 10mA current of a divider is a bit high for Q

Do u mean replacing the op-amp (the error amplifier) with the differential one stage amp?? Because i read about some CMFB architectures (check the images for examples) 118988 This is a good example for a differential one-stage opAmp. You could even save one differential pair (M23,

## 2 Stage Op-Amp Stability Analysis

Your latest simulation show the amplifier in overload, input differential voltage is much to high, in so far the results are meaningless for regular operation. Please repeat with reasonable parameters, resulting in non-distorted output.

## Noise Figure of a Balanced Amplifier

Hi everyone, I was wondering if you could help me prove that noise figure of a balanced amplifier equals the average of noise figures of the individual amplifiers, i.e. F = (Fa+Fb)/2 where Fa and Fb are the noise figures of the individual amplifiers. Thanks in advance

## [moved] ADS RF amplifier using CFY6608

I am trying to design an amplifier using CFY6608 in ADS. But I have not used this software before. I have the .s2p file. I have to do stability analysis separately using Data Items option, because s parameters are not available with the built in model I think. How can I perform stabiity analysis using bias network in this case? secondl

## Should I worry about stability due to harmonics in Class E PA design?

Hello all I'm designing a Class E PA at 13.56MHz. I find that Freescale MRFE6VS25N, which can work from 1.8MHz to 2GHz, is very suitable for my design. However, the wide working bandwidth makes a new issue: Will the amplifier be oscillating due to the harmonics which are s

## How to reduce S21 of an amplifier at undesired frequency to improve the stability?

Big boss, whether this feedback technique will work at 12Ghz? Can you please share,some practically implemented feedback circuit at higher frequencies like 10-12Ghz? Feedback is independent from the frequency, it's always applicable but there might also be some practical constraints.For instance I applied series feedb

## Simple-but-worthwhile stability check for SMPS feedback loop?

Hello, In a current mode flyback, compensated with a type 2 error amplifier, it is a fact that the error amplifier's high frequency pole should always be at a lower frequency than the frequency of the power stage ESR in order to assure you avoid instability Is this true? ie, ensuring the above won't assure stability but (...)

## Transimpedance amplifier vs normal op-amp

Yes - there is. 1.) The inverting input of the TIA is low-resistive (other name: Current-feedback amplifier); 2.) Open-loop "gain" is Vout/inout current: Transresistance; 3.) Due to stability there is a lower limit for the feedback resistor (specified by the manufacturer, range: 0.5...some kohms); no capacitive feedback allowed; 4.) The closed-loo

## Transimpedance amplifier. Gain and Phase margin

Probaly normal behaviour. Transimpedance amplifier is inverting, thus 180° phase shift observed. Phase decreases according to the poles in frequency characteristic.

## Help needed with fully differential amplifier design

Hi guys I need to design a fully differential amplifier having CMFB with a large Gain Bandwidth product of around 3Ghz. Also the settling time has to be less than 5ns. Closed loop gain is 15. Can a folded cascode achieve this in 180nm technology? Would I need two stages? Please advice on the topologies which can be considered. Thanks!

## Low noise amplifier stability, noise figure and gain

Hi all Got some screenshots attached for a low noise amplifier using an ATF-34143 FET from avago. The objective is to create this amplifer on a PCB with the following specs: 1. Unconditional stability across 0-18 GHz 2. S21 > 15dB between 1.5-1.6 GHz 3. noise figure < 1dB between 1.5-1.6 GHz The circuit performance pic shows the K factor

## Adjusting Differential Amp's Gain by Using MOSFETs

To analyze circuit stability, you need to know the MOSFET capacitances. I assume a TL082 in inverting amplifier configuration isn't stable with MOhm range feedback resistors due to the input capcitance generated pole.

## Is my amplifier oscillates?

I've already test it by a SA. During the test, the input port was connected with a 50Ohm matched load while the output port was connected with the SA. I didn't find any oscillation signal only some interference signal which is -50dBm at the output port. And those signals were turned out to be GSM and WIFI signals. My amplifie

## S Band LNA Design, but conditional stable at 16 GHz

Yes, if add all the parasitics of components may be possible to do not get the 16GHz oscillation. Do you see an oscillation, or the simulation give a potential unstable amplifier at that frequency (K<1)? Meantime potential unstable doesn't mean it will oscillate.

## Transistor |s21| less than 1 and still can serve as amplifier?

Hi all, Could it be that tha transistor's |s21| is less than 1 (50 Ohms) and still the MAG is high (say 20-22 dB)? How comes?

## What to do if a transistor unstable at an un-desired frequency

Input and output matching networks plays important role for the stability of the amplifier. Using high-pass topology for the input network, and low-pass for the output network helps to avoid low frequency (or very high frequency) instabilities.

## how can i design opamp ideal?

The term "ideal opamp" describes something that can't be actually made or designed in actual technology. It's e.g. required for circuit stability that the loop gain falls below unity at a finite frequency. For this reason, any amplifier to be used in a feedback configuration can't have frequency independent constant gain. The practical design ch

## Gain changes in Low Voltage Amplifier over the time

If resistor values are high and board is uncoated, even relative humidity could make that kind of change. At such low input level, Vio drift and things like charge pumping of ambient 60Hz/120Hz hum could be at play. A copper box and a known-stable voltage meter might be a good thing to try. I see "520mV" and "530mV" as being a bit short of resol

## Simple push- pull amplifier question

The 10mA is DC idle current in the output transistors to avoid crossover distortion. It has nothing to do with output power. The value of the input capacitor in your simulation is WAY TOO LOW! The simulation assumes a source impedance that is zero ohms. Since the input of your simple amplifier is a low impedance then 100nF cuts all frequencies bel

## Ldmos Amplifier Stability Issues

hi, I want to know the steps involved stabilizing the ldmos based amplifiers. I am using MRFE6S9125NR1. Somehow i was able to get 50 to 70 watts from 925 to 960MHz. But there is some stability issue in 880 to 915 band. ADS LSSP Simulation shows that that amplifiers becomes unstable at 33dbm input power. The (...)

## unstable MESFET amplifier

If you have put the Input and Output stability Circles here, I could say something more. K<1 doesn't mean that the amplifier will absolutely oscillate ( but it may!!). If you want to be sure about the stability, there are some techniques such as connecting a resistor at the drain or gate,small amount of negative feedback,emitter (...)

## differential amplifier

Hi, You can use an differential amplifier as a Buffer.... And the Rs and Cs are used for Phase margin and stability of your Diff-Amp... Diff-Amp is a simple form of an Op-amp.. Thanks..

## Increase K factor for stability

You can always stabilize an amplifier by doing things you definitely want to avoid. Simply putting resistance in the source can have a profound effect, such as allowing almost all impedance matches to be unconditionally connected. The price is it introduces a part that has a thermal noise component. Any resistive dissipative thing badly messes

## GSM Power Amplifier Stability Issue

Hi, I have designed a GSM amplifier using MRFE6S9125N.The band width is 915 to 960 MHz . The out put power is 40 watts. I followed matching networks given in the datasheet on FR4. This amplifier is working well without any problem. It ' gain was set to 16 or17 db by using VNA. This amplifier is working well for months. After this i (...)