# Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers, which are DC-coupled, high-gain electronic voltage amplifiers with a differential input and, usually, a single-ended output.

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63 views

### Programmable gain amp vs op-amp + digipot

I'm currently developing a system where I need a signal amplifier with variable gain. I'm browsing the market for viable chips, and it looks like I have two options: Programmable gain amplifier ...
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### How to determine the signs of the op-amps in this circuit?

I have tried assuming OPA1 has negative feedback and then find the sign of OPA2 making assumptions on the latter. But the answer turns out to be wrong. How should I proceed with this question?
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145 views

### How to derive the average current drawn by the op amp in the given circuit?

For the circuit, I have calculated the output current to be (pi/20)*cos(wt) and the average of this is 0. But, since the initial conditions tell Ip= Im= 3mA, I thought the average current will turn ...
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1 vote
184 views

### Where does my op-amp system of equations fall apart?

I was working on this problem: Find values for $\{R_2, R_3, R_4\}$ Assume ideal op-amp Gain of 100 Input resistance of $1M \Omega$ No resistor is larger than $1M \Omega$ And I build the ...
1 vote
173 views

### Transimpedance amplifier with OPA838 - oscillation - supply voltage

This post is the continuation of my previous post: Transimpedance amplifier with OPA838 - instability Considering there were a lot of discussion, so we made this new post, to add for details, such as ...
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1 vote
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### Understanding this constant power laser driver circuit

I am trying to reverse engineer a constant power laser driver. Unlike constant current drivers, these use an integrated photodiode which monitors the laser diode output. The photodiode current feeds ...
157 views

### Best Practices for Preventing Oscillations When Interfacing an ADC with an OPA Output

I'm working on interfacing an ADC with the output of an operational amplifier. To mitigate signal integrity issues, my usual approach includes placing a small resistor near the OPA output and a small ...
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426 views

### How to share a single gain resistor among multiple op-amps in a circuit

I'm currently designing a circuit where I need to implement multiple op-amps, each configured with the same variable gain resistor using a single digital potentiometer. To simplify the design and ...
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106 views

### Op-amp with significant noise

I have the circuit below on breadboard. (Photodiode connected to op-amp in Transimpedance configuration) With LF351N (placed on the breadboard) as op-amp I'm getting nice signal on oscilloscope ...
553 views

### Why doesn't my OP Amp comparator work in LTSpice? (AD8665)

When V2 > V1, Vout should output approx. 5.3V. When V2 < V1, Vout should be approx. 0V. But this op amp seems to always output 5.3V regardless what V2 is. What could be going on here? Is this ...
• 1,012
274 views

### Open loop gain of Op Amp 20 dB lower

I need some clarification regarding the open loop gain of Op Amp. I tried simulating this active BPF on LTspice. The Avol of the Op Amp U6 (UniversalOpamp) is 1meg and its GBW is 10meg. My ...
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41 views

### Frequency Companding

I have a theory question. I want to know if compressing and expanding audio frequencies is possible or perhaps already accomplished. As a point of reference, audio companding is a signal processing ...
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### Buffered power supply with op amps?

I dont quite understand how this circuit works. I tried to simulate it on multisim 14 and got even more confused! Can anyone help me analize this circuit? I only understand the second stage (the ...
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2k views

### Why does my integrator slowly saturate to negative rail in the following configuration?

So I have the following basic integrator circuit: The input signal is a 100mVp-p square wave of 50k frequency. In this case I get a stable triangle wave output. However, when I make the amplitude ...
173 views

### Simple example of first order ODE and Operational Amplifier

Hayt's (8th edition) Engineering Curcuit Analysis (Chapter 9, p360) contains an illustration of Operational Amplifier solving $\frac{d^2v}{dt^2} = -9v$. It is hard for me to understand how it was ...
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152 views

### Generate a fast, high amplitude pulse for measuring slew rate

I need to create a test set-up that measures slew rate of a few op-amps. The fastest slew rate among all of the op-amps in my list, belongs to NE5532 with 9 V/us slew rate and output amplitude of ±10 ...
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1 vote
61 views

### Time period of V1 and V2 signal the integrator and schmitt trigger

Hello I have tried to solve this circuit several times and i cant figure out what i did wrong. You guys give me some tips. This is circuit with 2 op amp (2 stages) first one is schmitt trigger and the ...
55 views

### Is it necessary to match the operating ranges of the two stages in a two-stage amplifier

I'm trying to design a two-stage amplifier as shown below. What confuses me is that - is it necessary to match the operating range of the two stages (ie. Vocm of the first stage is within the Vicm ...
• 625
103 views

### What is the quiescent current in a current limiting voltage regulator circuit?

Is the quiescent current simply the current drawn by Q1 and Rin when no load is connected to the output? How would this differ from the supply current?
980 views

### Implementing guard trace/ring in PCB design for opamp having high impedance input

In the circuit below I am trying to create a "guard ring" for the opamp with high input impedance (~1T Ohm) to avoid femtoampere current leakage. I'd like to ask you guys if I did it right. ...
1 vote
120 views

### Calculate the transfer function of an OPAMP circuit [closed]

I have an OPAMP circuit that its output increase steadily without cahnge in the input. I guess the issue is in the transfer function of the circuit and its stability. I want to calculate the transfer ...
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95 views

### Building a unity-gain op amp with speaker?

I am trying to build a voltage follower op-amp circuit to hear a sine wave but I can't get it to work. I was using the LM386 but then found out that it has a gain of 20 by default so I can't use it. I ...
129 views

### Excessive DC offset in high-speed opamp amplifier circuit

Background A while ago I got my dad's old Musical Fidelity A1 MKI integrated amplifier from the early 80s (I believe). I found a blog that featured a lot of interesting information about this ...
98 views

### How to measure fully differential amplifier input impedance in PSpice?

Before the differential ADC, I have a fully differential amplifier as the front end. I want to simulate and measure differential input impedance. My working range is max. 20 kHz. Why am I using the ...
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1 vote
82 views

### Using an LT1357CN8 to amplify the signal of a 1.5 MHz frequency generator

I am working on a frequency generator to control piezoelectric transducers. I use an Arduino Uno R4 Minima to send data to an AD9833 which creates my desired sine wave up to the required 1.5 MHz. ...
57 views

### Ground Fault Interrupter

I was trying to simulate a circuit where it can detect grounded neutral conditions in the household. I need to have a current transformer which can detect the current differential ans sends a signal ...
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752 views

### Slew rate and Bandwidth for 5 MHz signal

I'm trying to amplify a sine wave signal with opamps of high bandwidth and slew rate. It works fine up to about 700 kHz, then the gain decreases and about 1 MHz it's only 1, when it should be about 5. ...
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62 views

### Ideal headphones impedance/sensitivity for op-amp

The maximum output voltage of my audio source is 3 Vpp and the maximum output current of my amplifier (op-amp AD4075-2) is supposed to be 45 mA. What would be the ideal impedance and sensitivity of ...
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81 views

### Will voltage at the inputs/outputs destroy an unpowered opamp?

I have a circuit powered by 12V that accepts an input signal of 0V to 10V. The circuit shall act as a buffer to the signal, with an added LED indicator. In certain circumstances, the circuit itself ...
86 views

### Using a square and/or sine wave generator through a speaker [closed]

I have recently undergone some university study which introduced square and sine wave generators, I was wondering if there's a specific speaker I could use (its inputs would be a power supply and the ...
62 views

### Options for line output doubling as headphone output

As the title says, I'd like a combined line/headphone audio output with the following design criteria: ideally driven from 5V single supply (12V available, but noisy) flat frequency response, also in ...
55 views

### 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 ...
228 views

### Exercise of expressions for ideal op-amp based amplifier circuit

(i) Obtain an expression for the CMRR of a difference amplifier, in terms of the tolerance of the resistances used in the amplifier. Hint: Assume that 𝑅1/𝑅2=(𝑅3/𝑅4)(1+𝛼), where 𝛼 is the degree ...
90 views

### uA741 OpAmp output current never approaches "TYP" output short circuit current

I am trying to use a uA741 Op-Amp (I cannot use a different Op-Amp) to build an amplified half wave rectifier circuit. I was able to successfully build the circuit, however the zener diode that I used ...
54 views

### Virtual short condition contradicts the equation for an op amp output voltage [duplicate]

I'm trying to understand how to analyze basic op amp circuits. From what I have found, the output voltage of an op amp is equal to the following equation: ...
1 vote
97 views

### Op-Amp Selection for Dummies

I am new to op amps, and I could use some help. I am trying to make a linear precision current supply and searching for the perfect op amp for the job. I have a design I know that works, at least on ...
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58 views

### OpAmp Input Impedance vs Load resistance

I have below photodiode that provide low rise time based on 50 ohm load resistor. However I'm planning to use it with opamp in transimpedance configuration. In this configuration, current is running ...
1k views

### Why is the level wiper wired like this in the op-amp stage?

I have come across a mixer that I am going to rebuild, and maybe try to replace the volume potentiometers with a digital variant. The picture shows part of the schematics (after 3-band EQ, and before ...
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1 vote
148 views

### Op-amp with two series capacitors

Consider the circuit below. Let $V_i$ be switched on at t = 0. We want to find an expression that related the output voltage $V_o$ to the input $V_i$, in terms of R1, R2, C1, C2. Here is my ...
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57 views

### Using Laplace transform to solve integrator circuit

I need to find Vout in time domain for below circuit. Here's my attempt, using Laplace transform. $$V_{in}(t) = V_0 \sin(\omega t)$$ From the above equation, Vin in s-domain is then: V_{in}(s)=V_0\...
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201 views

### How can I find Thévenin equivalent circuit of the NFB op-amp input? [closed]

I need to find the Thévenin equivalent of the right side of the circuit by looking into node E and F. How can I find it?
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58 views

### capacitive soil moisture sensor connected to attiny85

je suis en cours de créer une circuit électronique d'un capteur d'humidité du sol capacitif avec un aop pour amplifier le signal sortie de capteur , et ce capteur relie avec le microcontrolleur ...
95 views

1 vote
95 views

### LTspice: triangle wave circuit not producing any waveform

I've implemented this circuit in LTspice from this Triangle Wave Generator tutorial. Unfortunately, when I run the simulation, it doesn't produce a wave at all, just a flat VDC output. Any help would ...
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67 views

### OpAmp on Multisim keep amplifying over Gain Bandwidth Product

I have below circuit on Multisim with Current source replicating Photodiode and opAmp amplify current. However opAmp keep amplifying even at very high frequencies without considering Gain Bandwidth ...
1 vote
78 views

### LTspice - simulation of SPWM is giving unexpected result

I am trying to make SPWM with op-amps. I also made a simple NOT gate with a simple transistor. The first op-amp is working well when its output is not connected. When I directly connect the first op-...
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### How to prevent this op-amp from railing

I have the following circuit: An input that can go negative (+/-5 V sine wave), and two inverting op-amps. The second op-amp is "current buffered" and is driving the base of a BJT. Here is ...
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