# Questions tagged [stability]

The ability of an electrical circuit to stop oscillating within a finite period of time. Related topics include the Nyquist stability criterion (and the associated Nyquist plot), Bode plots, and gain and phase margin.

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### Input Impedance of a converter and output impedance of battery

It is said that the output impedance of an EMI filter needs to be largely lower than the input impedance of a converter in order to have no stability issues. From this document written by Christophe ...
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### Propagation delay stability

I have been asked to find out propagation delay stability for LVDS --> LVDS splitter. I can see the values for propagation delay Min, Typ and Max in the component datasheets. For example part ...
1 vote
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### Unwanted sawtooth on LDO output

I'm using an LT3507A, which takes 12V to generate 1.2V,1.8V, and 3.3V on its switching regulators(primarily for an FPGA), as well as using the 4th LDO regulator to generate 1.8V for the 3 ADCs I have (...
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### Conditions for network stability [closed]

Apart from poles lying in the left half of the $s$-plane, there is one more condition for stability: If the transfer function is $H(s) = N(s)/D(s)$ then degree of $N(s)$ should be less than that ...
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### Selecting the compensation components, RCOMP and CCOMP, in a DC-DC converter

We know that in that selecting the compensation components, RCOMP and CCOMP, a DC-DC converter like the LM5155 is crucial for setting the control loop bandwidth and ensuring stable operation. These ...
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### Sizing the output capacitor of DC-DC convertor

My questions is continuation of my previous post: Adding capacitors to the power stage of a DC-DC convertor (SEPIC&CUK) My fist question is which capacitor in the circuit should be considered as ...
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1 vote
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### Adding capacitors to the power stage of a DC-DC convertor (SEPIC&CUK)

I'm working on the following reference design form TI: Based on the test report it can provide 50 mA to each rail and +60 V/-60 V. In my application there will be pulse current draw from this circuit ...
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### Wien bridge oscillates at 6x expected freq and amplitude oscillates too

A while ago I made a Wien bridge oscillator to go from ~500 Hz to ~1 MHz, using an NE5532 opamp and stabilizing amplitude with the typical opposing diodes method. Worked fine, but the output was too ...
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1 vote
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### BIBO stability and Asymptotic stability

I have difficulty solving these two exercises: Exercise 1 Consider the system described by the transfer function $$P(s)=(s-1)/(s+1)^2$$ Design a controller so that the feedback controlled system is ...
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1 vote
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### Need help analyzing sability of op-amp in a current source in LTSpice

I have to perform stability analysis on an op-amp (AD8671) which is being used as an op-amp in the circuit attached. I am using LTSpice to perform this. My approach is to give a 1V AC small signal at ...
86 views

### Issues with Audio Amplifier Circuit - No Output Signal with Capacitor, noise

I'm having trouble with an audio amplifier circuit that I designed, and I hope someone can help me figure out what's wrong. Here's the schematic of my circuit: Rsig is a variable resistor The circuit ...
181 views

### LTSpice simulation produced different results of phase margin when using step-signal % overshoot technique vs loop analysis technique

I am working on a class AB amplifier circuit to that can output both AC and DC current, controlled by an op-amp with feedback from the final output. The output will be driving an 50uH inductor. The ...
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### Keep the circuit stable even without the input capacitance on inverting pin of a transimpedance amplifier

I have designed an transimpedance amplifier for an ultrasound transducer as follows: Ultrasound transducer feature: C=1nF, R=1.2K, working frequency between 2-3 MHz When the transducer is connected ...
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### Stability of an ideal Differentiator with a "classical" Op Amp vs using a transimpedance amplifier

I have a question regarding the stability of an ideal op amp differentiator. Say I have the following circuit: simulate this circuit – Schematic created using CircuitLab Now calculating its ...
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### Can a high-precision, low-current voltage source "fix" drift in a lower-precision, high-current current source?

I'm trying to generate a current source which is extremely low drift but can maintain high current (3A into a few ohms), that should be similar to this expensive high-precision current source. However,...
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### Why do some op amps' datasheet specify phase margin at open loop?

I am not able to understand what significance phase margin would hold in case of open loop. Shouldn't it be just phase? If it was loop gain I'd understand specifying phase margin to denote stability. ...
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### Stability analysis - 0 dB crossover point

I have a question about Bode diagrams. For example if a Bode plot (gain) cross 2 time the 0 dB axis which point should we consider. Should we analyse both of them and keep them stable (good phase and ...
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### What could be the reason that one opamp oscillating but not the other?

This is ultimately related my previous question here. And I use the following circuit: When I try with this MCP opamp I get a DC output which I want since I want the average: But when I this OPA ...
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### Reasons for implementing op-amps which are not unity-gain stable

The datasheet for the OP37 boasts that the device is a low-noise, high-speed, precision op-amp. However, one reason why one may choose to not use the OP37 is that it is not unity gain stable. That is, ...
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When putting switch mode supplies in series with each other, or adding an input filter to a supply, I have used the Middlebrook criteria to check for stability. Chris Basso's other stack exchange ...
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### Micro switch capacitance on the inverting input pin of operational amplifier

I want to use a microswitch on the inverting pin of my transimpedance amplifier to be able to select two different channel of my transducer as follow: It the microswitch datasheet in is mentioned ...
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### Confusion with the sum of open-loop gain and feedback attenuation

Regarding the following statement taken from here: Looking at amplitude response on the log plot, circuit instability occurs when the sum of open-loop gain and feedback attenuation is greater than ...
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### Capacitance on op-amp input (inverting pin)

I have the following configuration for my amplifier, which is an transimpedance amplifier: I need to connect my transducer to the inverting pin of my amplifier by using a dip switch to be able to ...
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### How to measure overshoot of an op-amp without having an oscilloscope

I need to measure the overshoot of an op-amp but have no oscilloscope or other measuring device available. I should therefore have a circuit to do so. I have created an input pulse and want to apply ...
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### Filter non-inverting input of operation amplifiers or directly to GND?

In the following configuration on this operation amplifier (OPA838), which is transimpedance configuration, can I connected the non-inverting input directly to GND, or should I use this filter? Not ...
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### small signal overshoot reported in datasheet and stability

In datasheets of some op-amps namely ADA4522, NE5532, OP184 a small signal overshoot percentage has been reported mostly for an input pulse of 100mVp-p in a unity gain configuration. As far as I ...
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1 vote
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### Choosing isolation resistor for Op-amp output

I want to choose an accurate value for an isolation resistor for my OP-AMP (OPA838). Based on the datasheet, the OPA838 is very sensitive to capacitive loads and needs an isolation resistor added to ...
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### Bode criterion for stability - applicability conditions

While checking Bode criterion for stability, I found several sources disagreeing on what is needed to be able to use it. In general, every source I checked agrees that the open-loop system must be ...
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### Confusion about finding poles by inspection

I have a few doubts regarding finding poles by inspection and why sometimes the 'quick, intuitive' techniques do not work. Question 1 Consider the circuit shown in figure 1 below: By manually writing ...
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I designed an amplifier with an OPA838 as follows: First scenario: I want to connect the OPA838 to a next stage voltage LNA (Low Noise Amplifier). What components or circuit should I add to my output ...
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1 vote
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### PCB layout recommendation for Op-Amp [duplicate]

When designing a PCB for Op-amps normally there are some guidelines in the datasheet of the device. For example, for OPA838 the suggestions are: Signal routing must be direct and as short as possible ...
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### Why is a peak in the gain a sign of instability in a closed loop op-amp circuit?

I watched a tutorial video that mentioned that when there is a peak in gain (dB), it is a sign of instability in the op-amp circuit. Is this statement always correct? If yes, can any one please ...
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### Adding a capacitor to the output of an op-amp can cause instability? (PCB trace capacitance)

In my amplifier design, I checked all the possible issue for finding the instability problem in my previous post: Transimpedance amplifier with OPA838 - oscillation - supply voltage , Transimpedance ...
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### Adding a capacitor between positive and negative supply pin can cause stability issue in OpAmp circuit?

I have a transimpedance amplifier designed and when I apply +/- 2V to its supply pins it is oscillating, I noticed when I apply GND to V- supply pin, it does not oscillate, so I have a little bit ...
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### Nyquist stability criterion in discrete time domain

I've been transforming systems from the s-domain to the z-domain, and looking at the Nyquist plots I get in the z-domain. So far I've assumed that the Nyquist stability criterion that applies in the s-...
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### How to test the stability of an OTA in this case?

I am designing an OTA for a current buffer (images from Analog Design Essentials): The OTA is just used to provide a high gain, to regulate the voltage on RE. My question is, how to test the ...
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### About stability in system with loop gain AB>1 in negative feedback

I have been reading about stability and feedback systems, and a very silly issue has appeared. We can describe a negative feedback system as what can be seen in the following picture: Image source: ...
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### Stability of a constant current sink( opamp+nmos)

I am using opamp and a mosfet as constant current source. My current is from 0mA to 25mA. Opamp-TLV9002 (GBW-1Mhz at 5v , phase margin - 78deg at 5.5v and gain as 1 ) Mosfet- nmos- Bss123lt1g ( input ...
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### Injection point for stability analysis

According to the application note from OMICRON, for making good stability analysis of a converter, it is necessary to place the injection point at a certain place on the board : Does anyone know why ...
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### Does pole-splitting narrow or widen the bandwidth?

Razavi gives the answer of why the compensation capacitor should not be placed between the gate and drain of M3 transistor. Below are the quotations of his question and answer: Question: Explain why, ...
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### Poles of system seem counter intuitive

I have a system with the three poles 0+8i, 0-8i, and -0.5. When I input a sinusoidal signal, this is the output: Based on the poles, -0.5 is in the left side of the plane so it should be stable. +8i ...
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### How to compensate this circuit? [closed]

I'm using the circuit above to control the common-mode voltage of the 2 resistors. M16 is a current source. The OpAmp controls common-mode voltage by adjusting the resistance of M20. I need to adjust ...
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### Stability issue: Compensation changes using Bode plot in LTspice

I am encountering issues with a LT8390 design, particularly in higher load current conditions, which leads me to suspect a stability problem. The design parameters are as follows: vin 18-36 (28v ...
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### Transimpedance amplifier: weird simulation results

I am working on a photodiode transimpedance amplifier based on an OPA2374 and decided to simulate it in TINA TI. However, several unexpected issues arose. AOL and GBW product vary significantly with ...
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### Fundamentals of electrical circuits. Practice problem 16.13 Network Stability [closed]

I have this question from my Electrical Electronics textbook. After repeated efforts I still can't manage to solve it and the textbook doesn't provide enough information to be able to solve this ...
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### Continuous Time LTI system stability confusion

It is understood that if ROC of the transfer function of a system doesn’t not contain the $j\omega$ axis, then the system is unstable. I also know that if the transfer function of the system has any ...
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### How is a resonant bandpass filter similar/different from a damped mass-spring oscillator? They seem to behave different in testing

Background I am using resonant bandpass filters as musical oscillators. One can excite an array of them at harmonic frequencies and given Q values for a note by, for example, running a burst of noise ...
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### Avoiding overshoot in step response for robustness

In Systematic Design of Analog CMOS Circuits (Jespsers, Murmann) page 343, the following is stated in the context of where to place the non-dominant pole in a second-order loop transfer function of a ...
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### Exponential stability of a general $RLC$ circuit with sinusoidal input
I conjecture that any $RLC$ circuit with $n \ge 0$ independent sinusoidal voltage sources of the same frequency is exponentially stable. How to prove this or if this is not true, how to modify the ...