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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BGR explanation

Before asking the question I would like to attach the image of the BGR regarding which I have some doubts: From what I have read, due to the high gain of the op-amp, the two inputs of the op-amp, Va ...
1 vote
2 answers
28 views

RC Servo Auto-Sweep with Op amp Control

I'm trying to design a circuit that will sweep an RC servo motor (an SG90) continuously from -90deg to 90deg position and to repeat this process indefinitely. I'm aiming to use one IC (a quad op amp ...
3 votes
4 answers
334 views

concatenating first order high pass filters

I have the following circuit, which is an active high pass filter with the knee frequency \$ f_{-3dB} = \frac{1}{2\pi RC} = 1kHz\$ I wanted to concatenate two of those systems in order to make a ...
1 vote
2 answers
87 views

Twin-T notch filter with high input impedance and low output impedance using one op-amp

I have a very space and power constrained application, where I want to apply a twin-T notch filtering to an audio signal and add a little gain of about ~10x. The following filter section has the ...
3 votes
3 answers
320 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 ...
0 votes
2 answers
53 views

Op-Amp transistor voltage regulator considerations

I am trying to recreate a circuit that is mentioned here, here and in various other sources. For the project I intend on using this in it would be beneficial to be able to switch output voltage from ...
9 votes
3 answers
934 views

What is the purpose of putting resistors in series with current-feedback opamp supply pins?

Opamps U1/2/3 are current-feedback opamps used in a RF signal conditioning circuit. U1/2 control the gain through R8 and S1. U3 along with U7 allow for polarity toggling. What I don't understand is ...
1 vote
1 answer
524 views

Opamp isolation buffer behind phototransistor

Part of a PCB I designed looks like this: Simple phototransistor with a resistor to measure the voltage over. More light => more voltage over the resistor. However, the circuit behind the output ...
-1 votes
2 answers
64 views

Simulating ground cancelling output stage in LTspice [closed]

I've tried to simulate ground cancelling mentioned by Douglas here: The simulation cannot cancel ground noise: V3 is noise pollution, V2 is microphone signal generator, V1 main power. R8,R10,R9,C1 ...
3 votes
1 answer
90 views

LTspice working with a dual opamp

I need help understanding how to work with a dual op amp using all 8 pins. I downloaded a spice model for the RC4558 from TI's website, but it only has pins 1, 2, 3, 4(-) and 8(+). In my audio ...
0 votes
2 answers
138 views

Photodiode amplification circuit

I'm going to build photodiode amplification circuit which is then connected to ADS1115 controlled by Raspberry Pi, it has sampling 3.3k. The operational amplifier I ...
-1 votes
0 answers
24 views

Attenuate and amplifiy to get same signal

I have a signal generated by a sensor (0-10 V range). If it is passed through a potential divider and the signal is halved (0-5 V range), then I pass this signal through an instrumentation amplifier ...
-3 votes
2 answers
81 views

Op-amp with both inputs the same doesn't output zero [closed]

In the picture below: We have exactly the same input at both + and - pins of the op-amp's input (in the above picture, In1 and In2 are identical). Normally we must have a zero output all the time but ...
1 vote
3 answers
113 views

Resistor before output in inverting opamp

I found these schematics for an audio mixer. The main part of the schematic is shown below. A first stage of input buffers before each in line consisting of an opamp is not reproduced. I am only ...
1 vote
1 answer
57 views

Forcing the bias current of a voltage feedback amp into a larger Class AB by a resistor

Can I force any voltage feedback amp to flow current in one side of its output stage (therefore moderate over-biasing it to work in an extended class-AB area), by simply connecting a power resistor ...
2 votes
1 answer
52 views

Trying to use opamp to buffer BuckPuck control input - but it keeps blowing up

I'm trying to make a fairly simple circuit, which powers a few LEDs in series using a single BuckPuck 3021 (https://www.ledsupply.com/content/pdf/led-driver-luxdrive-buckpuck_documentation.pdf) The ...
8 votes
4 answers
3k views

Why is it called "slew rate"?

For curiosity reasons, I want to know why engineers used the term "slew rate" for this op-amp phenomenon, I mean "slew". I googled it and found this: "turn or slide violently ...
3 votes
2 answers
972 views

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 ...
0 votes
2 answers
165 views

How does the TDA7265 (bridge amplifier) work?

I'm trying to analyze how op amps work in this circuit: TDA7265 bridge amplifier To be specific, I'm not sure in what mode the op amps work here and how to calculate their gains.
0 votes
0 answers
30 views

Need help with modding HackRF One RTL-SDR card with right amp

I'm trying to modding HackRF One RTL-SDR card, regarding this RF amplifier can be damaged the card has problems with TX below 100 MHz, lots of users complain about burning the MGA-81563 chip on board, ...
1 vote
1 answer
85 views

Opamp resistor arrangement to get out of its noise

In the balanced line technoloy text, the author mentioned that we can't have a large resistor for R1 in this circuit: The author said: For a series-feedback stage, the input impedance can be made as ...
2 votes
1 answer
81 views

Transimpedance amplifier circuit not working

I am making a trans-impedance amplifier using AD549 op amp that simulates a current-to-voltage conversion on a satellite radiation detector. In my circuit, an ultra-high value resistor (10G) is placed ...
2 votes
0 answers
46 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 ...
0 votes
1 answer
582 views

Do you know how to add VEE and VCC power strips to op-amp in Cadence that will be fit for simulation?

This is the built in Cadence OPAmp. I need to add A capacitor to the VCC wirep and Ground the VEE wire however, there is clearly not a VEE or VCC on this op amp. Also, I know that I could manually ...
3 votes
1 answer
105 views

Photodiode bias in TIA?

When I see TIA schematics, I can see either the photodiode to GND or against VCC. What is the difference?
0 votes
1 answer
301 views

Inverted Op-Amp for Current Sensor Output

I'm having trouble understanding why the following circuit uses the inverting configuration rather than the non-inverting configuration for amplification. This design is from the Sparkfun Current ...
4 votes
2 answers
61 views

Biasing a DIY current feedback opamp

For a personal project, I'd like to make a discrete current feedback opamp. Here's a simplified schematic: The question is about how to bias Q3/Q4. For a nice class-AB output, the sum of both Vbe's ...
0 votes
1 answer
84 views

What exactly is +VCC and -VCC in op amps?

I was reading about op amps and got confused at the supply voltage part. If I connect a 9 V battery as supply does that mean +VCC is 9 and -VCC is 0 or +VCC is 9 and -VCC is also -9? And also the max ...
0 votes
1 answer
72 views

How to practically find the amplitude of a high frequency signal?

I had initially planned to use a standard peak detector circuit with an op amp of a much lower bandwidth than the signal I want to measure - my assumption was that given a high enough time domain the ...
1 vote
0 answers
40 views

Cascoded op-amp: What practically limits CMRR and input impedance?

I am interested to better understand the practical limitations to input impedance and common-mode rejection ratio in cascoded op-amp structures. I already simulated quite a bit, but I am running into ...
0 votes
1 answer
53 views

pH-4502C pH module - Deriving the NTC resistance value through a differential amplifier

I recently purchased a pH-4502C pH module online and started playing with it and figuring it out over the past week. I've found the circuit online and then checked the components and probed it to make ...
0 votes
0 answers
2k views

Circuit Design for Temperature Sensing PID Controller using Op-Amps

Basically, the idea is that I'll have a temperature sensor (LM35) that will sense the temperature of a certain metal can. This metal can is subjected to heat by a gas burner, and the gas burner's ...
2 votes
1 answer
45 views

Control PWM Volume

I am using Arduino's tone() function to produce some basic tunes. However, tone() does not have volume control. I did post about ...
0 votes
2 answers
82 views

Am I overloading my circuit?

I'm using op-amps as schmitt trigger and with the resistors in the wheatstone bridge I am trying to control the flow of current in the load. When the load resistance is not connect between the outputs ...
0 votes
2 answers
190 views

Understanding time constant of high pass filter at op amp input

In the circuit attached R17 is the burden resistor for a CT which measures 50/60 Hz currents. The switch is a CMOS analog one, not electromechanical. When the switch is closed, the gain is about R16/...
4 votes
3 answers
241 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 ...
0 votes
2 answers
93 views

Signal generator, DC offset, impedance into an open load - workarounds?

Video: MHS5200A Function Generator Review and Teardown I have the signal generator referenced in this video. As the video says, its output impedance is specified into an open load. It has a floating ...
1 vote
2 answers
64 views

Benefit of fully differential amplifier

I am trying to build an audio amplifier PCB with S/PDIF and single ended line level inputs and want to use the CS42528 CODEC (datasheet). My questions are regarding the input and output stages of this ...
3 votes
2 answers
2k views

SPICE simulation of voltage multiplier using log and antilog amplifier

I am trying to simulate a voltage multiplier circuit for positive DC input using logarithmic amplifiers and inverting adder implemented by op-amps(uA-741) and non-ideal diodes. The first stage takes ...
1 vote
0 answers
45 views

Is there a source for a TLC2272 model for LTSpice? [closed]

I'm an occasional user of LTSpice. I've found a couple of circuits I'd like to simulate that use the TLC2272 op amp, but LTSpice, no real surprise, doesn't offer TI part models. Do such models exist, ...
0 votes
3 answers
64 views

What type of op-amp configuration is this from a PLL circuit?

Can someone help me to understand this attached op-amp model? We are using it in an HMC3716 PLL circuit. We don't know how it works, exactly. Is it an integrator or a differentiator?
1 vote
6 answers
1k views

Why is a non inverting unity gain opamp's output not zero all the time?

In this circuit: simulate this circuit – Schematic created using CircuitLab The input is continually summing with its negative through negative feedback, so it must become zero on the output. ...
29 votes
6 answers
27k views

Does this photodiode circuit work?

Oli used this circuit in an answer, and it pops up a lot on Google images too. But does it work? If it does a theoretical explanation will be welcome.
4 votes
1 answer
2k views

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. ...
1 vote
2 answers
69 views

How to estimate the DC error for this input and opamp?

I need to amplify a 0 to 2.5 V range DAC output to obtain a -5 to +5 V range final output and I have some of these opamps to use. In my case the DAC output to be amplified looks as follows: Looking ...
2 votes
2 answers
84 views

High output impedance piezo guitar pickup is better attenuated by a shunt capacitor than an inverting opamp attenuation circuit

The circuit below is meant to attenuate a high output and high output impedance piezo electric guitar bridge pickup -7 dbV. The circuit models both the pickup output impedance and load of the cable ...
1 vote
1 answer
48 views

How would I have to modify this headphone amp circuit to increase the output power of one channel?

I'm currently trying to repair an old Sony TCD-D7 DAT-Walkman. It suffers from unbalanced audio output. The right channel is much quieter than the left one during playback. The headphone amplifier ...
3 votes
4 answers
380 views

How is the input offset voltage a function of common mode voltage?

I don't know about the internals of a opamps, but is it possible to explain how a change in common mode voltage changes input offset voltage Voff? I'm asking because when the signal Vin is fed to the ...
0 votes
1 answer
430 views

Op-amp failure and prevention

simulate this circuit – Schematic created using CircuitLab I'm a programmer and self-taught digital designer, and I thought I could deal with an op-amp even though I haven't for over 20 years. ...
0 votes
3 answers
161 views

Amplify millivolt signal with frequency to 5 VAC with frequency unchanged

Magnetick pickup waveform is in Blue I want to read the speed signal from a magnetic pickup. At low speed the signal voltage is in millivolts and it has a frequency which is equal to the number of ...

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