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.
973
questions with no upvoted or accepted answers
11
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1
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939
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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 ...
- 698
4
votes
4
answers
424
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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 ...
- 41
4
votes
0
answers
658
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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 ...
- 43
4
votes
1
answer
480
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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:...
- 153
3
votes
0
answers
76
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Circuit with resistance equal to input resistance
I want to use a digital potentiometer, however, the digital potentiometer has a power limit, which means I can't apply the voltage for my application.
I am looking for a circuit which functions as an &...
3
votes
1
answer
101
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Current source circuit components
I want to make a constant current driver for a laser diode (500 mA max.) based on the circuit shown below:
Here is my version:
In my case D2 and D3 represent the laser diode. There is a NC relay and ...
- 1,365
3
votes
0
answers
109
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Ultra-fast driver circuit for low-power LED
The goal is to drive a low power LED at a very high frequency, with pulses of ~10-100ns width in order to produce a very narrow burst of light. The pulses do not need to be closely packed together, ...
- 31
3
votes
0
answers
80
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Output voltage not stable - What is compensation with respect to DC-DC (buck converter)?
EDITS:
Input voltage range: 24V to 48V.
Changing the load current from 0.38A to 1.018A increases the mean output voltage from 12.779V to 13.26V. The supply should be producing 12.5V.
I'm using this ...
- 3,923
3
votes
1
answer
139
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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-...
- 867
3
votes
0
answers
87
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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 ...
- 81
3
votes
0
answers
122
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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 ...
- 41
3
votes
0
answers
124
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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 ...
- 153
3
votes
1
answer
116
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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 ...
- 31
3
votes
0
answers
497
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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 ...
- 31
3
votes
0
answers
196
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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 ...
- 161
3
votes
2
answers
158
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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 ...
- 840
3
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5
answers
420
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TIA Photodiode SFH7050
I'm working with SFH7050 chip, it contains 3 LEDs and a photodiode.
The datasheet suggests the next circuit:
But it doesn't mention how to calculate Rf nor Cf. Which values should I use and how are ...
- 75
3
votes
0
answers
89
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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 ...
- 2,535
3
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0
answers
744
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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 ...
- 1,911
3
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0
answers
314
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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 ...
- 137
3
votes
0
answers
142
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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 ...
- 1,167
3
votes
2
answers
1k
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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 ...
- 105
3
votes
2
answers
795
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Transimpedance amplifier calculating feedback capacitor
What is the correct way to calculate \$C_F\$ of the transimpedance amplifier? Since I have seen two different documents, and each has a different way to calculate it.
These two documents are:
Akshay ...
- 499
3
votes
0
answers
622
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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 ...
- 49
3
votes
3
answers
598
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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)=\...
- 331
3
votes
0
answers
987
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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 ...
- 672
3
votes
0
answers
1k
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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 ...
- 6,922
3
votes
0
answers
1k
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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 ...
3
votes
1
answer
727
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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 ...
- 306
2
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0
answers
39
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Why is connecting an analog servo distorting this PWM-wave?
I'm working on a project where I'm trying to steer an analog servo using a PWM-wave generated by this circuit. I found the circuit design from this article. It consists of three operational amplifiers ...
- 21
2
votes
0
answers
47
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Active load and current source purpose on NE5532
I'm trying to do some reverse engineering on the NE5532 schematic, but I can't understand how is designed the current source for the first stage. What I want to analyze now is in yellow on the picture....
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2
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0
answers
84
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How does this capacitance measurement op-amp circuit work?
I'm studying this scientific paper where a capacitance measurement is done with the circuit shown at page 3. For simplicity I reported it here:
A sinusoidal signal is applied at the input through a ...
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2
votes
1
answer
89
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How to design an opamp circuit for reactive load
I have an OPA548 IC which is a high-power op-amp. I am using it in non-inverting amplifier configuration as shown in the schematic.
The input signal is a ramp signal with low voltage 0.1 V and high ...
2
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0
answers
59
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Stability simulation - breaking the loop for a MOSFET - op-amp current source
The task at hand is to create a voltage controlled current source of 60 mA driving a valve coil (64 mH, 139 Ω). I am aware the MOSFET used is insufficient powerwise; it was a quick attempt to have a ...
- 535
2
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0
answers
177
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Op-amp gives attenuated output
I am using an OPA547 high voltage and high current op-amp.
V+ = 15 V
V- = GND or -15 V
Ilim is shorted with V-
Vout has a fb resistor of 1K. The output load is a 50-ohm resistor
Vin+ = 0 V (GND)
Vin- ...
2
votes
0
answers
63
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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
137
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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 ...
- 43
2
votes
0
answers
108
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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 ...
2
votes
0
answers
83
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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 – ...
- 53.3k
2
votes
0
answers
97
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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 ...
2
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1
answer
135
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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
146
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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
75
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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 ...
- 1,396
2
votes
0
answers
92
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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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2
votes
1
answer
102
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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 ...
- 16.8k
2
votes
2
answers
139
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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
132
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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 ...
- 21
2
votes
1
answer
142
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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. ...
- 865
2
votes
0
answers
94
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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 ...
- 16.8k
2
votes
1
answer
152
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Protecting unpowered op-amp, or how can I use 12V to switch 3.3V?
I'm designing a Eurorack synthesizer module which includes an MCU, DAC (TI DAC8565), and TL074 op-amp for scaling and buffering the DAC output.
In normal operation the module will operate from a +/-...
- 1,036