# 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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### Circuit that offsets input voltage to exactly 0 V

I am looking for a (op amp) circuit to offset $f(x)= \log(x)$ always to zero. More comprehensible is the explanation on the x-y plot below. Basically, it is possible to offset the voltage with an ...
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### Finding Thevenin voltage and resistance [closed]

I am struggling to find the Thevenin voltage and resistance across terminals A and B of the given circuit. I got as far as writing KCL at nodes 2 and 3, which gave this: v_\text{AB} = - G_2/G_1 e + ...
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### Why do some op amps' datasheet specify phase margin at open loop?

I am not able to understand what significance phase margin would hold in case of open loop. Shouldn't it be just phase? If it was loop gain I'd understand specifying phase margin to denote stability. ...
118 views

### Is my solution to this differential receiver circuit calculation correct?

I solved the difference receiver circuit problem in the picture with the following formula but I am not sure of its correctness because I do not have an answer key. I would like to discuss whether it ...
60 views

### Decreasing the input offset voltage of two stage opamp to below $1 \: \text{mV}$

I'm working on a two-stage opamp constituted by MOSFET transistors. The important specifications for this project are Open loop bandwidth of $30 \: \text{MHz}$ Closed loop gain of $2$ A standard ...
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### How to bias an input AC signal for active high-pass filter?

I have been trying to design a 2-way active crossover, with low-pass and high-pass channels. So far I got the desired frequency response but the transient response is not up to mark. Here is the ...
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### Why does this simple op amp create an AM modulated envelope over its carrier?

The circuit below is an ideal op amp (requires no power, can produce any output voltage) in LTSpice: LTSpice shows it amplifying the 159.155 kHZ input, as expected. But it also shows a 2500 kHz AM ...
• 1,135
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132 views

### Does this op amp connected to an LC tank amplify its resonant frequency?

The circuit below has a resonant frequency at 159.155 kHz and should amplify it: That's exactly what this sweep predicts: But,even when setting V1 to 159.155 kHz the transient analysis shows no ...
• 1,135
293 views

### Voltage Follower Circuit Output Issue

I'm using NE5534 OpAmp in a voltage follower configuration. No other parts, just the opamp. Power supply is 12VDC and GND. Vin is square pulse with 5V amplitude. However, after making prototype, I ...
210 views

### Instrumentation amp output not matching voltage drop in LTspice

I am trying to sample the voltage drop across different components at high frequencies, and figured the best way to do it was with an instrumentation amp so there's not much additional load placed on ...
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1 vote
243 views

### Best method to create stable solution in analog computer using op-amps

As a beginner in electronics and engaged primarily in mathematics, naturally I'd like to explore the wonderful world of analog computing. As my first attempt, I have created the following circuit ...
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for signal conditioning before feeding it to the ADC of a microcontroller, I have the circuit shown in the image below. The 12V comes from an external source, and my goal is to measure this voltage ...
72 views

### How to reduce propagation delay and mitigate dual-step transition

I am working on a circuit intended to protect digital output pins from the external voltages of the system on which they are designed to be used. I have built the circuit and found some "strange&...
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1 vote
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### Best place to add DC biasing

I'm working on a circuit where I have a CS4344 audio DAC feeding into a LM324 inverting amplifier that uses 1.2v as a reference voltage. I'm staring with the example circuit shown in the CS4344 ...
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### Selecting an opamp for a voltage follower circuit using a LTspice simulation

Consider the following circuit: simulate this circuit – Schematic created using CircuitLab It is used to supply a 6VDC device (represented by R3) with a 12V car battery. More context on why ...
• 377
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### Boost or buck audio input to minimum and maximum levels

Similar to Simple circuit to boost line-level audio Background: Some songs start out really quiet - Queen is notorious for this - and then eventually ramp up to passable audio levels. To hear them, ...
1 vote
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### Class AB amplifier voltage amplifier stage

I am design a 1W audio amplifier and i want to have 8V peak to peak output signal but if i increased the R4 resistor then the output signal would be clipped. My input is 0.3V max sinewave. Here is my ...
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### I want to combine four analog inputs into one output using two op amps. Is this feasible?

I'm doing my first project with electronics and I'm trying to figure out how to make an Arduino read input from four identical sensors using one analog pin. I'm using multiplexers on my other sensors, ...
485 views

### How to Adjust Comparator Output Voltage for Circuit to Work at 3.3V Instead of 5V?

I recreated the IR LED/Photodiode circuit shown in the Circuit Digest article Interfacing IR Sensor Module with Arduino. My interest being to use it to sense/measure RPM of rotating equipment. The ...
97 views

### How does one add a volume control to this circuit?

My uneducated guess is to add a potentiometer at R6. Can anyone confirm? Image courtesy : amplifiercircuit.net
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### DC Offset of a single-ended OTA

I'm confused by the concept of DC offset voltage. According to this application note by TI, DC offset seems to be the result of the asymmetry (Vth, bias current, etc.) - they only consider the '...
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### The problem with hysteresis is in the comparator circuit with a mosfet. Oscillations during switching

In one of the design guides, I came across a circuit of a comparator with hysteresis. I modeled it in LTspice and built the circuit as shown in the figure. However, when I tested it with real ...
76 views

### Opamp input signals not ideal but output is correct

got this old circuit. Rectangular pulses (red) look not ideal but somehow output pulse is a clean waveform. Is this because of the 2.5VDC voltage always present at inverting input of U1? I ...
123 views

### Pulse generation from a constant current source

I need to generate a biphasic pulse as shown below. [![enter image description here][1]][1] The specifications of the pulse is given below. Amplitude 0~10mA Pulse width 10~500µs Constant inter-pulse ...
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### negative OpAmp output with LM7705 on the ground pin

Can someone help me understand why I'm measuring -0.23V on the output of the MAX44285 OpAmp when I add the LM7705 -0.23V supply to the ground as shown? According to this reference design LINK, it ...
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### MOSFET Operational Amplifier

I am confused. Why we always say that the gain of an op amp should be as large as we can? Supposing that an op amp has a power supply of 1.8 V, the voltage gain is 1000 V/V. If we give a small signal ...
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### Should I merge GND and COM?

I'm building an dual supply op-amp circuit. I'm using a Isolated DC-DC converter module to supply op-amp with +-15V. The module ouput is labeled 'COM' and isolated from the input GND. The input signal ...
1 vote
533 views

### Photodiode Circuit Output Saturating to 0V. Is there a way to salvage these boards?

My colleague and I recently designed and ordered a PCB intended to capture red laser light using a SFH2440 photodiode. We used the analog devices photodiode circuit design wizard to design the ...
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1 vote
51 views

### IR pulse sensor : signal stops after a few pulses

I'm trying to make a pulse sensor based on this tutorial: https://makezine.com/projects/ir-pulse-sensor/. I therefore reproduced this diagram by replacing the LM354s with MCP6002s and without ...
404 views

### LTspice third party model gives problem with transient analsys

I have tried to import a third party model from TI, to be precise the op-amp A551. And somehow my circuite, a power amplifier, gives me the following error. Analysis: Time step too small; time = 3....
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### TIA beta factor

I read in Wikipedia the circuit and operation of the transimpedance amplifier. I elaborated on this website the steps to find the transfer function. I do not understand how to calculate the feedback ...
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### Audio Op-Amp Query

I came across this circuit recently: Here is my analysis from a glance: Resistor divider R1 and R2 set the DAC point for Vinp. The microphone, Rmic and C1 cause AC perturbations on Vinp. At low ...
1 vote
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### PIR Circuit Problem

I am using D203B model of PIR and I used the circuit that was suggested on its datasheet (first pic). I do not know what the problem is, as the output (pin the 8 and 14) of op-amp (LM324)is always on (...
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### Gain bandwidth calculation of two stage op-amp

I want to design a two stage single ended OTA without using a Miller compensation capacitance. Every source that I have examined gives a design example with a compensation capacitance. Hence, they ...
1 vote
48 views

### What happens when the value of resistances used in a differential input filter for a current sense amplifier circuit is too small?

I am working on a current sense amplifier circuit with the following configuration: While the circuit works, the filter is not performing as intended. Specifically, it should act as a low-pass filter ...
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1 vote
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### Differential Amplifier Output Ringing

I designed this circuit. It is a fully differential amplifier of gain one. I am getting this ringing and noise on the output of tx1_o Blue is where the probe is and ground is on circuit's ground. Here ...
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### What could be the reason that one opamp oscillating but not the other?

This is ultimately related my previous question here. And I use the following circuit: When I try with this MCP opamp I get a DC output which I want since I want the average: But when I this OPA ...
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### How can i obtain a positive Vref for this circuit?

I have to design a irrigation system that uses a resistive moisture sensor to maintain a certain level of relative soil humidity for a plant. In order to convert the resistance changes of the moisture ...
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### DAC errors and voltage mapping (0.3-3v to 0-2.7v)

Using MSP0G1505 MCU. It has a inbuilt DAC. I thought it could give me 0 to vdd as output but it seems it can only give 0.3 to vdd-0.3 as output. This happens because of the offset and gain errors. ...
115 views

### Is it possible to design a circuit with an op-amp that always keeps the output voltage 1 volt higher than the input voltage?

Is it possible to design a circuit with an op-amp that always keeps the output voltage 1 volt higher than the input voltage? For example, if the input is 1V, the output should be 2V; if the input is ...
49 views

### Methods For Reducing Output Voltage Of Pressure Sensor Into ADC

I am developing a data acquisition system that takes pressure readings from a pressure sensor. The pressure sensor is a bridge sensor which feeds into a differential ADC. The ADC has an input range of ...
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### EKG active filter designs with single power supply

This is my beginners attempt at designing a EKG. I have printed out the PCB and attached all components to it to test it out. What I have observed are the following: 1. The outputs Vout1 as well as ...
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### Differential input resistance of non-symmetric circuits

In Sedra and Smith (7th edition, section 2.4.1) when building up to an instrumentation amplifier there is discussion of how to use a single op-amp (differential input, single-ended output) to ...
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### Why does my common mode test still have tiny retained sine wave?

I used this equipment the BMA-200 with the AMP01 having a CMRR of 125dB. I connected the signal generator output to both the In+ and In-. Yet the waveform still have retained sine wave of very small ...
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### Sinking and sourcing current from and to the output of the op-amp

I need to have a set-up to sink and source current from the output of an op-amp to measure the maximum output current of an op-amp. This is the test set-up I thought of: If the maximum output swing is ...
353 views

### Common Mode Rejection tests

What's the best equipment for testing the common mode rejection of an op-amp? Like can I use an ordinary signal generator and just connect the one output to both inputs of the op-amp? Or is there a ...
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### Unreasonably low slew-rate of a DAC0800 and TL072-based waveform generator

I'm building a simple waveform generator based on the Raspberry Pi Pico, a DAC0800 IC and a TL072 op amp. The circuit works, but the slew-rate is - I believe - unreasonably low for the components I'm ...
2k views

### Reasons for implementing op-amps which are not unity-gain stable

The datasheet for the OP37 boasts that the device is a low-noise, high-speed, precision op-amp. However, one reason why one may choose to not use the OP37 is that it is not unity gain stable. That is, ...
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### A basic question about loop gain and stability

I read that we want to avoid loop gain of -1 to avoid instability in opamps. But does that mean loop gain of -2 or -50 is fine as long as loop gain is never -1?
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