Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers,

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3
votes
2answers
259 views

Reducing effect of MOSFET parasitic capacitance with resistor in series with gate

I have a MOSFET in series with the output of my amplifier to switch the amplifier output to the downstream circuitry. The MOSFET parasitic capacitance is seen as a load capacitance by my amplifier, ...
1
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1answer
112 views

How to plot the open-loop gain of an inverting amp, difference amp, and low pass filter?

For example, if we are using the ADA4004-1 op amp in all these circuits, the open loop gain is 400000 as shown in the spec sheet (Table 2): ADA4004 Datasheet The open-loop breakpoint is at 30 Hz (...
0
votes
2answers
53 views

Op-Amp - Sharing Non-Inverting Inputs in a two stage amplifier

I've mocked up a simple circuit using a TL064A to reduce the single level of a single ended input audio source. I'm using two stages per channel, and both stages on each channel are sharing a ...
1
vote
1answer
41 views

Testing spice model for common mode rejection ratio?

I've been trying to create a circuit to simulate common mode rejection ratio of an op amp to test the spice model's accuracy. While I've seen online that being able to use exact resistors only a ...
5
votes
1answer
1k views

Working of transistor in an Opamp log amplifier..?

In the figure it could also be possible to connect the transistor Q1 as a diode by shorting its collector with its base ..but instead it is done by keeping both base and collector at ground... The ...
0
votes
1answer
27 views

Electronic Circuit with Opamp and Transistor to pull down a reference voltage via a diode. (Voltage Limiting)

I have a circuit which I have designed to pull down a voltage via sinking current into the opamp output. When the source signal is of higher output impedance this works fine, but when the source ...
5
votes
2answers
155 views

Current Regulation Drift

Over a 200ms period of which this circuit regulates a 500mA current, the current drift downwards for about 0.4%. At first I thought it was due to R202 temperature coefficient, but from my calculation ...
1
vote
3answers
105 views

Current Source Output Does Not Become 0

I put a simple current source on a circuit to drive a UV LED with a constant current. According to the LTSpice simulation setting 0 V at the signal input results in 0 A through the LED. But when I ...
0
votes
3answers
137 views

Three Different Voltage Lines, Same Common Ground?

I am trying to send PWM, clock, latch and blank signals from Arduino through a series (16) of TLC5940 Breakout boards and on to a grid of 512 individual controlled LEDs six feet away (RJ45). I am ...
0
votes
3answers
58 views

Understanding this comparator circuit for AC voltage protection

The circuit shown below is taken from this whole design. I understand the main idea. They want to measure some voltage condition and trigger something else with the comparator. R39 and C38 form a low ...
6
votes
2answers
2k views

Crowbar circuit causes unexpected behavior for op amp circuit

I am using an op amp to amplify an input signal from a microcontroller, which in general is working fine. For over voltage protection, I added the crowbar circuit taken directly from figure 32, page ...
2
votes
4answers
100 views

operational amplifier CMRR measurement

I am trying to measure CMRR of an op-amp and I found an application note from Analog Devices, that suggests the circuit below. I understand what CMRR means, but I can't understand why in the formula ...
0
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1answer
46 views

Sampling Frequency and Bandwidth

If i have a Buck Regulator switching at 200KHz and i want to sample the Voltage and current using OpAmp in tha path connected to ADC(12 bit). What would be the sampling frequency to measure the ...
0
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3answers
100 views

Negative Voltage Shift from Blocking Cap for Amplifier

Recently I have been working with the Analog Devices AD797 op-amp in LTspice, and have been getting poor performance from the amplifier when using a low-amplitude signal. This is my circuit in LTspice:...
0
votes
1answer
38 views

Floating input in Op-amp Readout Circuit?

I was analyzing this circuit diagram in a thesis about a capacitive EEG electrode. The author talks about a flaw in the design where there is a "floating analogue input" that is causing the op-amp to ...
0
votes
1answer
100 views

What kind of amplifier design is this?

I am dissecting a design and I'm trying to wrap my head around the design pictured below. It is based on the TL064C amplifier and takes in single ended audio and outputs single ended audio as well. ...
0
votes
1answer
35 views

feedback loop component dc converter

Consider the schematics below, the switching frequency is 250KHz, So, The cross over frequency be 250/5 = 50KHz. My ADC is able to sample at 1MS/s which is good as from the SNR perspective.Now, the ...
0
votes
1answer
40 views

summing amplifier output

i amplified 2 audio signals using lm386 ics separately,and gave both the outputs as input to ua741 ic,to be used as a summing amplifier.I am not able to get any output at the speaker from ua741,not ...
0
votes
1answer
102 views

K1803 Velleman Pspice problem

I have an assignment to simulate in and output in pspice and compare my results to what i messured in real life using functiongenerator, oscilloscope and generator. The problem is i dont know how to ...
0
votes
2answers
47 views

Amplifier Audio Ground to Signal Ground

I am using a VS1053 (on a SparkFun Music Maker shield) to provide audio for my project. I am taking a line out signal and inputting it into an op amp for signal processing, ultimately being input to ...
0
votes
1answer
116 views

Transimpedance Amplifiers on PCB

I have several transimpedance amplifiers on my board, and I want to avoid the need for a negative power supply, but I can't see any way around it (except for running the current through a resistor but ...
1
vote
1answer
106 views

Questions from a current regulating and measuring circuit

In my previous question I asked about a simple topology suggestions for regulation of highish currents(around 10A) especially for resistive heating elements in 1...10 Ohm range. I concluded to use a ...
6
votes
6answers
2k views

Why does this potentiometer in an op-amp feedback path cause noise when adjusted?

I have placed a dual-gang 100k potentiometer in the feedback path of two op-amps that work as a Sallen-Key filters. This controls gain but also the Q factor of the filter (somewhat demonstrated on ...
0
votes
2answers
105 views

Back feeding when connecting one side of circuit to differential op-amp

simulate this circuit – Schematic created using CircuitLab I am building four 30v voltage sensing circuits to measure battery+/battery-, load+/load-, battery+/load- and battery-/load+ voltages ...
1
vote
1answer
104 views

Single Ended Precision Variable Amplitude Square Waves and Charge Injection

I love to hear any thoughts about a good break-before-make analog switch with low charge injection or even even better any thoughts on generating precision amplitude square waves in general. As to ...
1
vote
2answers
31 views

Can I use piezo plate instead of electret mic?

I am doing a project by following the steps mentioned here. It provides me the following circuit: Now, in place of the electret mic can I use a piezo plate? I need to use the same IC, i.e. LM358. ...
0
votes
0answers
25 views

Multisim opamp output oscillates for DC volt if it reaches saturation

Am trying to learn op-amps using Multisim. In the simulation I set initial condition to zero and set the circuit so the output reaches saturation point but instead its ringing with frequency 374HZ. I ...
1
vote
3answers
165 views

Precision with opamp in transimpedance amplifier configuration with LED as photodiode

I found this circuit in searching for a circuit that uses LED to measure absorbance What I want to ask is: in order to "accurate" the readings from \$ V_{out} \$, for example: assume that the current ...
1
vote
1answer
125 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:...
2
votes
1answer
83 views

What's wrong with this circuit built on opamps?

I have built this circuit in the LTSpice, but it refuses to simulate the operation using normal solver, but shows great results using alternate. This source says Be suspicious of circuits that need ...
0
votes
0answers
39 views

calculate the ouptut of two operational amplifiers in a series

i want to calculate Vs which is the output of this circuit simulate this circuit – Schematic created using CircuitLab so i just want to equation that can help me find Vs. please help me, ...
0
votes
1answer
43 views

Abuse TS339 comparator channel as a voltage multiplier

I have multiple free channels of a TS339 amplifier remaining and would like to use one of them to multiply voltages like this: simulate this circuit – Schematic created using CircuitLab Now it'...
1
vote
1answer
109 views

Function of diode in the following circuit schematic?

I feel that I have a semi-solid understanding of op-amps (and the circuit above) after reading quite a few explanations online. Where I'm starting to get quite lost is the function of the two diodes ...
0
votes
2answers
59 views

Op Amp integrator (square to triangle) not always start working correctly

I created an Op Amp integrator with LM358 to convert square wave to triangle wave as shown below. simulate this circuit – Schematic created using CircuitLab Though the circuit sometimes works ...
0
votes
1answer
243 views

Turning off op amp for low power application high side or low side

I have a design where I am using a LM324 to act as a buffer (unity gain impedence transformation amplifier) to feed the voltage from several high-impendence voltage dividers into my MCU's ADC pins. ...
1
vote
2answers
84 views

Help With Buffer Amplifier/Filter Type Circuit

I’m having trouble with a circuit I designed and I would be greatly appreciative if I can get some help here. The circuit I designed is a buffer amplifier type design intended to take two channels of ...
0
votes
1answer
121 views

Voltage drop when driving voice coil OpAmp gain stage

I'm driving a voice coil with a PID controller. So far, I've set the gain (P) stage, which is composed of LM358 opamps and a dual +-4.22 rail with 1.5V AAA batteries. This is the schematic, where you ...
1
vote
1answer
70 views

High voltage op amp rail generation

I'm using two ADHV4702-1 high voltage op amps for a project. They are configured as a current sink with a class B output amplifier (with some fixes for the crossover distortion). I already have a +/-...
0
votes
1answer
160 views

Op amp zener clamp design

What are the drawbacks of this design vs a design like the TI one here? Should the feedback be on the other side of R2? Are there any other gotchas using something like this, vs limiting using a 7v+-...
3
votes
2answers
95 views

Calculate right leg drive integrator

My question intersects with "What does this op-amp circuit do? (part of an ECG)", but I need some more detailed clarification on the opamp integrator of this right leg drive circuit as found in the ...
7
votes
2answers
1k views

Why is opamp slew rate specified at unity gain?

Is there some reason besides convention to add the "at unity gain" qualifier? Does adding or omitting it communicate something about the component? Are the opamps which have a slew rate that varies ...
0
votes
1answer
87 views

High side current sensing

I want to sense 30 amps of current using op amp in high side. I know that there are many dedicated current sensing amplifiers for this purpose. But I'd like to try it with an op amp. I have tried high ...
-1
votes
0answers
35 views

How to drive lcd display?

I'm trying to figure out the basics of LCD screens in practice. I found a good video which tells it needs negative and positive voltage https://youtu.be/ZP0KxZl5N2o?t=767 I want to drive just one ...
0
votes
3answers
88 views

Op-amp input impedance

I was reading the following tutorial from Analog Devices: https://www.analog.com/media/en/training-seminars/tutorials/MT-040.pdf They include the following image and state: In most op amp ...
4
votes
3answers
104 views

JFET stabilised wien bridge component ratios

I find myself in need of a sine wave oscillator and have decided on the wien bridge. I have followed all the tutorials but have a few questions that do not seem to be answered elsewhere. Firstly, I ...
-3
votes
1answer
68 views

I just purchased a batch of TL081CP opamps and would like to know what the codes on the bottom mean [closed]

There is a random marking on each one. none the same. What does this mean? e.g. 03, 1h31 In my batch, none are the same with leads me to think they would not be bach codes.
2
votes
1answer
104 views

Can I use a JFET like this?

I'm trying to bias the inputs of an op amp, I can't simply use a resistor because there is a tiny cap at the input and it forms a voltage divider and I get no signal through. Can I use a JFET like ...
1
vote
0answers
52 views

Designing a 4053 IC robotic control circuit for interfacing with Sabertooth motor controller?

I am designing a control circuit for a robot and was recommended to use a 4053 IC to achieve analogue multiplexing. PROBLEM The Sabertooth 2x60 motor controller I am using is running in analog ...
0
votes
1answer
25 views

Gain with inversing Op Amp on Equalizer

I know I posted a question about this circuit before, but I'm running into a problem. I know this is a terrible equalizer design but I'm trying to learn to put in use what I learnt with Op Amps and ...
7
votes
5answers
5k views

Any downside to using a charge pump for an op-amp negative supply

Background: I'm often building audio op-amp circuits for various purposes, and for small projects usually prefer single "wall adapter" supply. So for a ground reference I'll either use a simple ...