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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Convert analog piezo "transition" to digital signal

I'm trying to get what amounts to a knock indication into a microcontroller input from a piezo sensor. It's looking fairly good now at the fifth iteration, and about ready to provide digital levels ...
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5 votes
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89 views

Is this cascoded opamp structure unstable by design (LTspice)?

I am playing with a cascode op-amp design and I have problems judging its stability (schematic at the end of the post). When I judge the DC or AC analyses, it all looks good. No peaking and good phase ...
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How to show opamp noise contribution in LTspice .noise calculation

When doing system noise calculations using LTspice using the .noise instruction, I can plot the total output noise and I can plot all the individual noise contributions to output noise from all ...
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4 votes
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571 views

PIN Photodiode gamma detection amplifier circuit - rectangular wave output

I've been working on a project recently, where I need to build a device which detects gamma radiation and can be used for gamma spectroscopy. I've done some research and found many interesting ways of ...
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1 answer
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Common audio signal voltage range on Line out connector

What is typical audio signal voltage range on Line out connector of consumer electronic devices? (Vmin/Vmax) I need specify Input voltage range to calculate op-amp. ...
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4 votes
3 answers
271 views

Problem with simple non-inverting NE5532 configuration

I am building a small amplifier which is working just fine. While experimenting I interchanged the TL072s with NE5532s and the amplifier stopped working, so I set up a simple non-inverting amplifier ...
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3 votes
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83 views

W/L ratio analog design

I hope someone can help me. I’m designing a two-stage op-amp in LTspice. ...
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1 answer
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Confusion with using non-inverting input to fix common mode voltage

Regarding this paper, and the following diagram: We can see above that the non-inverting input of U2 is connected to Vref of the DAC. Signal input goes to the inverting input and Vref to the non-...
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Nodal Analysis of an Inverting Operational Amplifier

I am trying to derive the closed-loop gain of a basic Inverting Op-Amp circuit using nodal analysis and the model that includes its non-ideal parameters. The equation I derived is incorrect, and it's ...
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What makes an op-amp good for electret microphone preamp vs other op-amps?

What makes an op-amp good for use in an electret microphone preamp vs other op-amps? Being JFET, current bias, voltage bias, etc? Does an op-amp that requires a negative voltage supply work better or ...
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  • 41
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Fixing overshoot in current regulation of AC electronic load

My AC electronic load (previous question here) shall have a constant-current mode. It is being simulated in LTspice. @devnull helped design the circuit for AC loads, but for simplicity's sake in the ...
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  • 143
3 votes
1 answer
109 views

Dual supply op-amp, 0V on input yet small voltage on the out

I've been working on a constant current source design and have come up with the schematic below (heavily inspired from the LTC6082 datasheet), however, there is a small issue. When my input voltage is ...
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What is the upper frequency limit for an op-amp integrator?

I'm designing a circuit to process a di/dt signal. As the input is the differential of the measured current, I have to integrate the voltage to provide a representation of the current. The duration of ...
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Wheatstone bridge with 3 op amps breadboard help

I have a wheatstone bridge like the following: I then want to connect it to a couple of op-amps: I tried doing it like this: Op-amp pinout: However, I can't seem to get it to work. Have i ...
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3 votes
2 answers
132 views

Need help with an IR demodulation circuit

I'm trying to reverse engineer a PCB and made a schematic. The bad thing is I only have PCB images from both sides, not the actual PCB. This PCB is used to detect a very small black object spinning at ...
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Audio amp IC: how does this output stage work?

I'm looking at an audio amplifier integrated circuit and the output stage seems a bit unusual. Has anyone seen this style of output stage, and does it have a name? And can anyone fill in the details ...
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3 votes
1 answer
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Opamp gain calculation

May be a very basic question, I am a chemical engineer with limited electronics knowledge. The circuit is a potentiostat with the current source \$I\$ being a sensor electrode. I was looking for a ...
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3 votes
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581 views

Comparator with hysteresis calculation

I'm trying to calculate the hysteresis of the comparator using currents but something isn't right. I'd like a little help to find the hysteresis thresholds without the simplified equations. simulate ...
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3 votes
1 answer
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Phase margin is 90° but transient step response shows overshoot

The Bode plot of the loop is as shown here: The transient step response looks like this: The block diagram looks something like this - basically a single stage op-amp (OPAMP in figure) with high ...
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237 views

Transimpedance AMP, Active HPF, phototransistor

So this is the part where I would like the phototransistor (TEMT6000X01) to be able to clearly capture an LED with a frequency flashing on and off at 1kHz. So what I have here is a transimpedance ...
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  • 137
3 votes
3 answers
330 views

Measuring voltages from different sources sharing Common ground that might differ slightly

I have a design with resistor dividers and low pass RC filters dropping down 0-32V to ADC range of 0-1.8V. With multiple channels, I attempt to measure voltages from different voltage sources on a ...
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3 votes
0 answers
115 views

CA3140 wideband output amplifier

The following circuit is nearly exactly what I need for the output stage of my function generator: datasheet: https://www.renesas.com/us/en/www/doc/datasheet/ca3140-a.pdf What I don't understand is ...
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3 votes
2 answers
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Op-amp circuit stability (LTSpice)

I want to study the stability of my op-amp circuit with LTSpice. I found this video as tutorial: tutorial on phase margin So, I did the simulation with closed and open loop as suggested and got the ...
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559 views

Piezoelectric transducer impedance and phase measurement

I have a circuit comprising of LT1210 current feedback amplifier (supply voltage = +/-15V, gain = 4) and its output is connected to a transformer (RM10 N97) with N=16.6 (150/9) which is further ...
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3 votes
1 answer
402 views

Buffer, amplify, filter, sample - In which order?

I'm trying get an audio signal from a high impedance source (guitar or mic) to an ADC. Some casual research suggested that I should filter my signal before amplifying it. My current mental design is:...
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  • 143
3 votes
3 answers
495 views

Finding the transfer function of an op amp filter circuit

I have the following third order filter circuit: simulate this circuit – Schematic created using CircuitLab And I know that the transfer function looks like: $$\mathscr{H}\left(\text{s}\right)=\...
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Complete Noise Analysis: to find the minimum detectable signal of a TIA

Problem Statement: my aim is to digitalize a 10ns narrow pulse coming from a photo diode with current ranging from 10nA-70mA, as its impossible to cover this dynamic range of >60dB using a single TIA ...
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3 votes
0 answers
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Deriving PI controller transfer function when input is reversed

I'm developing the compensator for the linear DC Bench Power Supply I'm designing. As I've come to deriving the transfer function for the op amp-based compensator, I realize I've been depending on a ...
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3 votes
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100kHz active filter design

I am designing a basic 100kHz active bandpass filter using opamps (LF353). I am only interested in receiving the 100kHz frequency (might drift a few kHz) from my input signal. I have used a basic ...
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3 votes
1 answer
644 views

Single supply op amp with input attenuator

I'm designing a guitar headphone amplifier that uses a single supply op-amp as the output stage to the headphones. I'm using a potentiometer after the final JFET stage and before the op-amps as a ...
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2 votes
0 answers
49 views

AD826 low gain after around 1MHz

I am using AD826 op amp to convert differential current sinked DAC output operating at 50 mega samples per second. DAC is fed a 3MHz sine wave by a FPGA. Output of the DAC is fed to the opamp with ...
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2 votes
1 answer
89 views

Op Amp Error Calculation

I am attempting to calculate the total error in an op amp (OPA2333 to be specific) that is used in a voltage sensing circuit. If I use the OPA2333 model in my SPICE circuit, are the errors already ...
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2 votes
0 answers
74 views

MOSFET - Frequency response

I tried to do an exercise from my textbook where I have to discover the gain for mid frequencies of the MOSFET below, but I can't solve it. I got stuck at one point. I drew the small signal ...
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2 votes
0 answers
47 views

Linear Analog Optocoupler Arrangements

For optocouplers with a second photodiode for feedback for linearization, what is the functional difference between the two positive input stage configurations below? simulate this circuit – ...
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2 votes
0 answers
55 views

Current through op-amp feedback resistor

Image source: Fundamentals of Electric Circuits by Alexander and Sadiku. 5th Edition. Page 182 Can someone explain to me how 26.25uA is the correct answer here? I am getting 11.25uA. If I assume ...
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2 votes
1 answer
118 views

Triangular waveform with low noise

I have a task to generate a triangular signal with variable amplitude and support. The figure shows the type of signal and what parameters I want to change (“d” and “o”). Moreover, I need to change ...
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2 votes
1 answer
85 views

LM317 current limiting/set via differential amplifier works in simulator but glitchy when built

I am trying to build a single LM317 power supply, with current limiting using a differential opamp and potentiometers. I've came up with this (see schematic) and have built it on a breadboard but the ...
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2 votes
0 answers
56 views

Input bias incorrrect in stock LTspice model

I am trying to use the AD8067 in LTspice (v17.0.33.0). The model for this opamp ships with LTspice. I have rigged it up as a follower, and I am seeing 150pA input current. Per the datasheet it should ...
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2 votes
0 answers
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Making a low-cost in situ fluorometer with Arduino

I am making a low cost in situ fluorometer with Arduino based on this paper The paper lists all the instruments required for the device, but since some of the products were outdated/hard to find, I ...
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  • 23
2 votes
1 answer
130 views

About Negative Gain in Bode Plot regarding the Op-amp Circuit Design and its Relationship with the Feedback Resistor

I am new to the circuit simulation and now I am using Tina to simulate a op-amp circuit for a photodetector. I have some questions regarding the bode plot. Below is the circuit design, based on the ...
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2 votes
1 answer
76 views

How much current can opamps' integrated ESD diodes carry during an ESD strike?

So the basic answer to such kinds of questions is usually: "If nothing is specified in the datasheet, assume the most conservative rating!" However, the datasheets usually only mention the ...
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2 votes
2 answers
124 views

Noise spikes on power line cause false readings

I'm working on a project to measure the frequency of a small voltage (~0.1V peak-to-peak, with 1.4 VDC offset) sine wave of 1-100Hz. I only care about the frequency. I'm using a LM324 quad op amp (...
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2 votes
0 answers
131 views

An amplifier that can output 40..50 V at around 15 MHz

I'm trying to build something to amplify a signal to produce a 40 V output at 15 MHz. I haven't been successful in finding an opamp that can both output at these voltages while also not dropping the ...
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2 votes
1 answer
114 views

Estimating load capacitance when connecting two opamps?

I plan to use the OPA657 as a charge sensitive pre-amplifier for measuring the output from a reverse biased PIN photodiode. I would like to further amplify the signal using a wideband EL5163 opamp. ...
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2 votes
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60 views

Op Amp Input noise and bias current relation with input quiscient current

I am trying to understand how varying the input differential pair quiscient current in an op amp will affect its: a) input bias current, b) input current noise, c) input voltage noise. Based on ...
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2 votes
0 answers
179 views

CW Doppler probe for fetal doppler and 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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  • 135
2 votes
0 answers
152 views

two stage op amp's PSRR

I recently study about two stage amp. In Sedra-Smith, it stays that PSRR for VDD is very small, and ignores this. To understand this, I set Q6's source Vin and Q6 is acting like a common gate ...
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2 votes
1 answer
45 views

calculate op amp outputs problem separately

I was quite confused of this problem since I cannot find the Vo2 using KCL for Vo1 - Vo2 but in the problem, it just said dont use KCL for output voltage. Is it the way op amp operating or I am ...
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2 votes
0 answers
644 views

How to measure Common Mode Range and Output Swing of a CMOS Differential Amplifier in LTspice

I'm designing a CMOS opamp in LTspice here is my current design. The amplifier obtains a DC gain of roughly 50dB and has a phase margin of 70 degrees at a ω (unity gain frequency) = 250 MHz. I'm also ...
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2 votes
0 answers
2k views

How to represent a microphone using a voltage dependent current source in LTspice?

I am using the following schematic and I'm trying to simulate it in LTspice but I am not sure how to represent the microphone. My instructor said I should use a voltage dependent current source but I ...
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