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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12 views

How do I transform a unipolar signal to bipolar signal?

I am trying to design a circuit that will convert a unipolar 0 - 12V square wave signal of about 1kHz to a bipolar +/- 12V signal. I have tried using a differential amplifier design approach similar ...
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2answers
34 views

astable multivibrator using OpAmps - why does it start?

Im a newbie in electronics and I'm learning some circuits with opAmps and now I have been shown this astable multivibrator. I understand how it works. OpAmp is saturated at one side or the other ...
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1answer
35 views

Understanding Negative feedback loop circuit with an Ideal Op-Amp

The following is given as an example of a negative feedback loop in my textbook, note that the op amp is assumed to be ideal. However I do not seem to get the logic behind this acting as a negative ...
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13 views

Understanding Negative feedback loop circuit with an Ideal Op-Amp

The following is given as an example of a negative feedback loop in my textbook, note that the op-amp is assumed to be ideal. However I do not seem to understand the logic behind this acting as a ...
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0answers
38 views

Ultrasound piezo crystal and doppler for blood flow velocity

I am currently working on a microcontroller based project to measure the blood flow velocity using ultrasound doppler. I have purchased two Spengler 8 MHz continuous mode probes in order to measure ...
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53 views

Boosting an analog voltage signal

I have a 0-3.3V analog DC signal and want to change that into a 0-5V analog DC signal? How should I go about doing this? An op-amp? DC boost converter? If it is an op-amp, what does the circuit ...
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2answers
48 views

Find Vo of an op-amp circuit

simulate this circuit – Schematic created using CircuitLab I've tried solving for Vo in two ways, one is I took V+ by voltage divider getting V+ = V1(R2/R1+R2) = 0.05V. Since V+ = V-, it follows ...
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1answer
115 views

Why does this opamp have a diode on v+

I was working on a layout for a guitar effect, and noticed on the schematic that 1 opamp has a 1N4148 diode on V+. IC6 on the schematic below. Given it has an internal power supply, I'm assuming ...
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2answers
102 views

Common mode impedance in operational amplifier

While looking at this simulation, as they say no current flows at the non inverting terminal of the op-amp, but looking at the differential stage of the operational amplifier shouldn't there be some ...
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1answer
34 views

Op-amp Power Dissipation Calculation for a pulse output

I am trying to calculate the power dissipation of the op-amp for a circuit as below. I am wondering if I did it correctly. Can anyone provide any tutorial on this? So this opamp will output ...
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6answers
671 views

RC oscillator with op amps

I am a physics student at a university and because of the pandemic, I and my classmates have to simulate our electronics lab exercises in Micro-Cap (version 12). We've got schematics like in this ...
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4answers
205 views

How do i solve a circuit when a capacitor is between in op amp inputs?

I am quite confused with this circuit. Most circuits I have seen don't have a capacitor between the op amp inputs. I tried to write out the differential equations using nodes, but I can't find enough ...
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66 views

Opamp Compensation For Input Capacitance

I am going through the datasheet of LM7171 for one of my applications. Please see the below circuit. May I know how they arrived at the equation for CF? Is this equation is valid for non-inverting ...
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2answers
61 views

What are the advantages and disadvantages of a Darlington pair? [closed]

Can the BJT transistors in a Darlington pair be of different types?What are the advantages and disadvantages of a Darlington pair? Is such a circuit able to generate power by itself?
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2answers
33 views

Does op-amp open loop gain change with DC input voltages versus small-signal AC input

I was wondering whether or not DC voltages can be amplified by op-amps. I thought about a typical Miller op-amp structure (differential pair input) and I suppose it could amplify a DC voltage. I am ...
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2answers
70 views

What is an op-amp's differential input impedance?

I've heard of differential voltages, but the concept of a differential impedance is new to me. Suppose we are trying to calculate/derive the differential input impedance of the following difference ...
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2answers
130 views

Which is the input resistance of the second amplifier?

If a apply a positive Vs, then D2 is blocked and D1 is working, right? How do I calculate Vo then? I know the formula is: - (input resistance / negative feedback resistor) * Vs, but I don't know which ...
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1answer
86 views

PWM with op-amp, but can't figure out formulas/how it works

I want to make a way to control the high time with a control voltage, instead of using a variable resistor. For this I have found this diagram with an op-amp, and I have tested it in Multisim (a ...
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49 views

Clarification on amplifiers

Can I use 2 LM311 in place of 1 LM385mm? LM385MM is a dual operational amplifier and LM311 is a differential amplifier so according to me we can use, it is just that LM385mm is low power device so it ...
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1answer
47 views

Laser diode driver circuit analysis help

I'm looking up for some circuitry to drive my laser diode and I came across this tutorial. I understand the basic operation of this schematic; however, there's one thing that confuses me: I cannot ...
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2answers
85 views

Ideal Op-Amp obeys virtual ground principle without negative feedback?

I was reading this book - 'Fundamentals of Electric Circuits - Alexander, Sadiku'. I came across this: They say that a characteristic of an ideal op-amp is that v1 = v2. I was taught that this is ...
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1answer
88 views

How do you regulate a car battery down to exactly / not more than 12V?

My problem: I want to light up the inside of transporters with a 12V LED strip. But I don't think powering it with the 12V car battery directly is a good idea. Although the name implies 12V, a car ...
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1answer
60 views

Design a non inverting amplifier [closed]

Design a non inverting amplifier of 26 dB gain and input impedence of 47 k ohm(the circuit at the top. Edit: thank you guys but I got the whole thing right just by practice. It wasn't an exam it was ...
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3answers
73 views

Where to connect unused pins operational amplifier

I am using a couple of OPA2227UA op-amps for a analog circuit. Since these are dual-op amps, one of them ended up unconnected. (The +-In/Out B pins shown below): The datasheet says what can I do for ...
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3answers
69 views

Op-Amp buffer Enable/Disable

I am designing an electric veichle controller for a University project. The motor driver receives an analog signal (0-12V) to adjust the speed. I use a digipot followed by a buffer to convert the ...
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1answer
61 views

Why is input resistance parallel with the base of BJT?

I'm solving for the third stage. The resistance looking into the base of Q7 is taken between its base terminal and ground as follows during small signal analysis for single end gain of Second Stage ...
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1answer
40 views

Observation of negative voltage at the output of the op-amp

I am using ADA4898 op-amp. Without connecting any elements to the circuit at the output of the IC, I see a negative voltage. Is my IC broken? simulate this circuit – Schematic created using ...
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2answers
37 views

How to superimpose 2 signals to test op amp circuit noise inmunity

I have a simple circuit with uses a non-inverting op amp. Just for the shake of my learning, I want to add some noise to the op. amp.'s input and see if I can remove it applying filters. To do this, I ...
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0answers
51 views

How are this voltage source and resistor (separated from each other by a capacitor) re-imagined as a resistive voltage source?

I'm trying to implement a wave digital filter from this research paper: Emulation of Operational Amplifiers and Diodes in Audio Distortion Circuits R. C. D. de Paiva, S. D Angelo, J. Pakarinen, and V. ...
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4answers
586 views

Op-amp homework question using potentiometer with my attempt at solving it

I nearly understood that when Rpot is 0, Vo is highest and when Rpot is 0, Vo is lowest. So I tried KCL to get Vo when Rpot is 0 (0 turns). I couldn't get Vo but just 0 volts. What mistake did I make?...
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9 views

Why am I getting a lesser negative threshold voltage for my astable multivibrator?

I've calculated my threshold voltages to be +/-5V but when I probe Vout, I'm getting a -6.42V threshold voltage instead of the expected -5. Why is this? I'm guessing it has something to do with R4 and ...
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1answer
114 views

Inverting op amp not working

I'm trying to wire a simple inverting op amp circuit just to test it. I have been unable to make it work. This is the circuit I have: I have simulated this circuit and it gives 1.92V (it should be -1....
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2answers
67 views

The purpose of capacitor between positive and negative in TIA circuit

I want to know what is purpose of C1 in below transimpedance amplifier, and how you calculate it. Without the C1 the output should be equal to : Vout = VGND - Is*RF (Vout can not exceed VCC) Note: ...
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46 views

Transimpedance amplifier design advice

I'm working on a transimpedance amplifier for a phototransistor in order to create a sensor that counts objects falling down a pipe. This is the sensor: https://www.digikey.it/short/0vq01q7h Datasheet:...
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15 views

Looking for a pin-compatible to LT1013DID rail-to-rail in/out op-amp

I have designed a circuit using LT1013DID (SOIC 8 footprint) op-amp and while Spice simulation worked, I forgot about input common-mode voltage limit (which it seems is not simulated) and thus need an ...
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3answers
80 views

Offsetting Op-Amp output offset in combination with charge pump

I want to have a +-12.0V square wave output from an opamp fed from a 3.3 and 5V power supply. The signal is 2.5kHz with a low duty cycle of 3-10% generated by an MCU. Peak voltage at both ends need to ...
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59 views

I can't understand how to make Vout and Vin formula

I started learn about comparators, but the concepts are difficult for me. I found the above figure in this link.
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2answers
59 views

Bandwidth and frequency confusion

This picture is taken from this answer. As far as I know, the bandwidth is the range of frequencies at which the gain does not go below 70.7% of its maximum gain. As we can see the author said when ...
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1answer
53 views

Constant Gain-Bandwidth product in amplifiers

Can somebody explain to me how the gain-bandwidth product is constant in an amplifier or op-amp? I want to know the mathematical expression behind it if possible. As said here: https://en.wikipedia....
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5answers
181 views

Why in op-amp inverting circuits one of the op-amp inputs is grounded?

Why the input have to be grounded in Op-amps? What does it do? How does op-amp sense the input voltage difference?
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2answers
69 views

Resistor values for a non-inverting op-amp with gain of 2

I'm trying to build a circuit that uses a non-inverting op-amp to double the voltage in the circuit. The op amp I'm planning on using is: http://www.farnell.com/datasheets/2258629.pdf , and I think it ...
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2answers
58 views

Dithering Circuit using an Op-amp

I am reading and trying to understand this Application note from TI on how the dithering circuit works. I can deduce that the Op-amp acts as a schmitt trigger but there's no details on how the ...
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2answers
67 views

Level shifting a 0-5V signal to 0-16V

I have a Atmel microcontroller with 0-5V DAC output and I want to shift it to 0-16V (16V max. normal between 11-16V). It need an output signal with max. ~1mA, short protection and reverse polarity ...
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2answers
46 views

Why is this buffered rail splitter oscillating and how can I compensate it?

Inspired by the question Op amp Power supply splitter with totem pole I played with the buffered rail splitter in LTspice. I placed a current sink as load on the output to simulate the current ...
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2answers
111 views

I am facing a problem while designing a Schmitt trigger circuit

I am applying a Schmitt-trigger to the waveform given in the figure below. . This is a 3.5 volt signal and I want to perform thresholding so I use 1.58 volts as upper threshold and 1.17 volts as lower ...
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2answers
75 views

Darlington biasing design error in a commercial frequency counter oven control circuit?

I am repairing a commercial frequency counter (brand to remain anonymous) that had the crystal oven visibly overheat. There is a small PCB in the oven that holds the crystals, the oscillator circuit, ...
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3answers
68 views

Analog signal level shifting and opamp selection advice

I wanted to read out and output 5-ish volt analog signals from a 3.3v mcu. So basically the signal (roughly 0.25v to 4.5v) first has to be level shifted "down", processed and then level ...
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3answers
196 views

Op amp Power supply splitter with totem pole

I want to make a +- 2.5V rail from a 5V supply using an op-amp. I was wondering if I could use a totem pole for driving the output like this: Image from here But while I was looking at it, I noticed ...
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0answers
39 views

purpose of feedback capacitor in operational amplifier

Can someone explain what is the reason of using feedback capacitor in an amplifier? does it even matter if we don't use it?
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2answers
592 views

Amplify difference between two photodiodes

I have two adjacent photodiodes in photovoltaic mode, with two transimpedance amplifiers. Unfortunately, my MCU (nRF52840) is one meter away, and I expect a fair amount of noise to enter the system. ...

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