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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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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stable vco with 10% tuning range [closed]

Currently I am using this vco https://www.crystek.com/home/vco/cvcodetail.aspx?pn=CVCO55CL-0042-0046 I have designed a pll loop using a stable signal generator as input. I have measured a significant ...
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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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Connecting an op-amp to a second-stage amplifier: loading effect considerations

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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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 bandgap width?

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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1 answer
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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 ...
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Any standards or limits for Voltage Angle value of MV system?

Are there any standards or regulations that specify allowable range or permissible limits for voltage angle value? For example, 7° of voltage angle exists at MV voltage level, so is it harmful for ...
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Allowable process variation for non minimum phase plant

Scenario (plant model subject to process variations) Consider a plant \$P(s)\$ in series with a controller \$D(s)\$ with a negative feedback path around it, where the closed loop is given by the ...
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LTspice IV: Stability of op-amp circuits

I am studying the stability of op-amp circuits using LTspice with the help of this video. I can see many threads on Stack Exchange like this one, but the explanation is not clear to me. I have a ...
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Low LDO output capacitance (stability)

I need to replace the REG104 LDO (End of life) in a circuit where the max. allowed LDO output capacitance is 100 nF because of explosion proof intrinsic safety requirements. The REG104 LDO is stable ...
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Op-amp feedback and stability

I have 2 questions related to this circuit. 1 The first question concerns the open-loop gain. I am tasked with finding both the open-loop and closed-loop gain. The closed-loop gain is calculated ...
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Potential issues with an alternative charge amplifier op-amp circuit?

Sorry in advance for a long question. I'm working on designing some pre-amplifiers to amplify signals from a Multi-Wire Proportional Chamber for a nuclear physics experiment. Each signal from these ...
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Phase shift at half the switching frequency of a dc-dc converter

I would like to know if, regardless of the control loop used (Voltage mode control, average current mode control, peak/valley current mode control), there is always a 90-degree phase drop at FSW/2 due ...
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Can an RCL circuit be asymptotically unstable? If so, what does that mean physically?

I'm analyzing the asymptotic stability of the system of ODEs that comes from an RCL circuit in series. Below is my circuit, with battery voltage \$u(t)\$, resistor with constant \$R>0\$, capacitor ...
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How to choose the value of the slope compensation?

I do not understand how RICHTEK as chosen its slope compensation. The article is here. The parameters of the buck are the following: Vin = 12 V Iout = 3 A Lout = 10 uH Fsw = 340 kHz Vout = 3.3 V The ...
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SIMPLIS - Buck CM from C. Basso Website

I took from the website of Christophe Basso a simplis simulation. I have some questions about it to be sure to understand it. Here is the schematic of the simulation: It is a current mode buck ...
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How is the number of crosses of -180 line calculated from the bode plot?

On the page 28/46 of the slide here: On the page 42/46: How are N_ and N_ equal to 1/2 here? I think it should have been N_ = 0 and N+ = 1.
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Would a solderless breadboard be able to handle 20V without short circuiting?

Until I can get a 12V power supply, I'm left with using a laptop charger as a power supply for my solderless breadboard. Will the breadboard be able to handle it?
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How is this ADC voltage reference buffer not unstable?

See attached images. They show an ADC voltage reference buffer with 22uF of output capacitance, a graph of the OPA350 stability with capacitive load and isolation resistance, and an ADI document about ...
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Why will an ideal double integrator oscillator only oscillate at one frequency?

I am trying to learn about RF oscillators. Example 8.6 in the oscillator chapterof RF Microelectronics 2nd edition by Razavi asks to solve for the frequency and amplitude of the oscillation of an ...
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DC-DC current mode control frequency behavior

On a buck converter in average current control mode, for example, the inner current loop sees and manages the double pole created by the LC filter, and thanks to this the outer voltage loop is blind ...
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Amplifier matching network, biasing circuit, and stability consideration

In amplifier design, it is essential to achieve proper biasing for the desired operating conditions, ensure maximum power transfer through matching, and maintain stability of the device. But, I'm ...
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3 answers
190 views

Is this LDO instability a real problem or a model bug? [closed]

Here is an LTSPICE simulation for which I just have an LDO (ADP7118) in its recommended environment and some reasonable parasitics. It is unstable as you can see in the transient plot (showing the ...
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Non-standard injection point to measure loop stability of SMPS

I have come across this document https://www.ti.com/seclit/ml/slup386/slup386.pdf , where injection points for stability measurement are discussed in Fig.26. For point 3 it says: "Because the op ...
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Telling loop instability from ringing

In the application note https://www.analog.com/media/en/technical-documentation/application-notes/an149fa.pdf unwanted oscillations are said to be caused by either loop instability or other ...
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LDO stability with resistor in the feedback path

I am working on a circuit for measuring very low and very "fast" currents (think: measuring power consumption of an MCU). I found out that I can measure what I want with a sense amp and a ...
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Variable switch mode power supply design problem

I have an issue understanding the working of a variable switch mode power supply. The power supply uses the reference voltage at the potentiometer and transfers into the VFB or feedback. Suppose I ...
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Deriving a transfer function from Nyquist plot

I am given a half Nyquist plot and exercise as below I know how to plot a Nyquist curve for a given transfer function but I have trouble doing it the other way. I stumbled upon this post Deriving ...
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LC filter out of the loop if crossover frequency is below resonant frequency?

Referring to slides 78-84 of http://powersimtof.com/Downloads/PPTs/Chris%20Basso%20APEC%20seminar%202009.pdf, the RLC network rings alone and the oscillations are not due to the loop. It is my ...
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Low frequency asymmetrical led blinking circuit, lacking thermal stability

I'm trying to use a NE555D to achieve a 500ms on, 1500ms off, duty cycle. The exact timing is not that important(+-20%). But my problem is that when the temperature changes it greatly effects the ...
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Instability as seen in time domain

It is my understanding that an unstable closed loop in a minimum-phase system occurs when the loop gain (A*B of the characteristic equation) encircles the -1 point on the Nyquist chart. In https://www....
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Nyquist Plot Stability with Angle

I don't understand the solution done here. The Nyquist criteria I know is Z=N+P and I don't see the relation with this solution. Where do the angles come from?
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