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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54 views

AC signal gets unwanted DC offset when connected to circuit

Hi im a 4th year ELE student and I am creating a circuit which outputs 120khz square wave burst when it detects zero crossings from the input ac signal. Here is the circuit diagram Op amp 1 converts ...
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65 views

Battery Capacity Tester - Schematic Review

I designed a circuit to test Lithium battery (3.7v) capacity. My measurements do not need to precise but should be relatively accurate between each batteries so think this should do. Schematics: Using ...
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150 views

How to analyze this opamp circuit?

So with the following circuit (currently studying for an exam): I am able to get V- just through the voltage divider composed of 2R and R at the non inverting terminal. However, once there, I am ...
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91 views

Low-frequency high.pass filter drifts with temperature

for a phase sensitive measurement, I would like to have the DC offset of a signal cancelled. The AC-signal will be amplified and then the phase of it is measured in reference to another AC-signal. My ...
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73 views

Can the direct current output of a photodiode pass through a capacitor? If so what effect are they having in this circuit?

I am studying RC filtering in order to try and understand this circuit which was previously discussed in(What kind of filtering does this op-amp perform?). The answers gave advice on testing the ...
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2answers
36 views

Different voltages for Single and Dual-supply (INA)

Since it doesn't matter for the Op. Amp. itself, the components presented as "single-supply" commonly relate to rail-to-rail input/output devices, which operate on lower total voltage ...
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39 views

What is the role of bleeder resistor and how to choose the right value?

I'm curious to know the role of bleeder resistance of 1k ohm at non-inverting terminal used in this circuit attached below. Is there any calculations to set the right value for this bleeder resistance ...
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76 views

Can I use an LM324 as a buffer amplifier or voltage follower for ADC reading with an ATmega328?

I am looking to read an analogue voltage from a pressure sensor. For that application, I don't want to connect the pressure sensor directly to Atmega328P ADC input as it might alter the original ...
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25 views

Dependence of the PWM amplitude of the amplifier on the battery voltage

I'm going to use speaker connected to internal Class D amplifier in WM8998 in my PCB. Power source of my PCB is Li-Pol battery with 3.2-4.1V range or external 4V adapter. Audio codec speaker power ...
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643 views

Op-amp voltage follower not working as expected

I previously asked about a circuit to scale my analog value before MCU ADC. Based on the answers I got from that post I decided to change my op-amp from a TL072 to a CA3130. The following pictures ...
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43 views

SAR ADC driver circuit: charge bucket and OpAmp GBW

I need a theoretical clarification about how to design a driver circuit for a SAR ADC. simulate this circuit – Schematic created using CircuitLab I found an interesting video series (https://...
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110 views

Non-ideal Non-inverting op amp

This is probably more of an algebra question. I do not understand where the "1"s come from in equation 1.10 given the much simpler voltage divider equation in the line just above it. And why ...
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64 views

Understanding input bias current in operational amplifier

In order to prevent overvoltages on my arduino voltmeter (more than 20v) I decide to add a protection circuit. As i show in the image i use a AD8605 precision op-amp for the purpose. (https://www....
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354 views

What is an instrumentation amplifier and how does the AD524 work?

I am struggling with instrumentation amplifiers. Particularly, I would like to know what defines an instrumentation amplifier what kind of circuit configuration could be classified as an ...
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96 views

How do I get the formula to calculate the frequency of this oscillator?

I looked for a relaxation oscillator for my project. Then I found this: I tested it on simulator, and it works fine. But I need to calculate the frequency of this oscillator to put capacitors and ...
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88 views

Electret microphone for ADC input

I'm currently working on a fun PCB project and have this circuit built that will input into an ATmega328P. What I'm looking for is what you guys think of this and if you think it will work. Does the ...
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62 views

LM336 Zener diode and LM759 opamp circuit as a stable DC 5 volt power supply generator

I would you to help me to understand a circuit I have in my notes which is reported in the following picture. First of all it's my first time in which I see the supply voltage in some ways connected ...
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1answer
53 views

How difficult is building an op amp circuit with datasheet performance?

I want to build a simple voltage follower to buffer headphones with the OPA1688. It will just be built on protoboard, considering how simple the circuit is I think it should still be possible to ...
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30 views

OpAmp Buffer (S11 > 1)

I have the following buffer schematic set up: I am trying to understand why the S11 Parameter goes out of the unity gain circle, which indicates that the buffer schematic reflects more power than is ...
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2answers
148 views

Inverting opamp amplifier

The gain of an ideal opamp is considered infinite and Vout=K(V+ - V-). where V+ is the non-inverting input and V- is the inverting input. The output voltage in the case of an inverting opamp amplifier ...
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50 views

LTSpice (windows) - current labelling

I want to measure current going into and out of an op-amp. However, when I do .op command, I am not able to understand which current is being referred to here. ...
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3answers
109 views

Feedback in Integrator Amplifier of Op-Amp

Why in analog computers for the integrator amplifier the feedback resistor is not applied? So, how to make sure (apart from resistors configuration) that circuit operates in linear phase?
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44 views

Operational amplifier - why average voltage is not stright related to pulse to duty cycle?

I have a strange problem, that I cant find an answer. I have slow photodiode (about 2MHz) and fast, pulsed laser light source (pulses 10 to 500ns). Im trying to measure optical output power. To do it ...
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78 views

Why do op amps need input protection when the input impedance is very high?

From what I understand, the input impedance of an op amp is very high (ideally infinite) and almost no current flows into the op amp. If that is the case why do we put a resistor in series with the ...
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54 views

Unity gain buffer giving DC out

I am feeding square wave (0-5V) at 1kHz through a AD713JNZ op amp which I have wired up as a unity gain buffer, but I'm getting 5V DC on the output: What am I doing wrong?
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226 views

Understanding analog frontend for PIR sensor

I read this application note from Texas Instruments to learn something about the design of an analog frontend for PIR sensors, but I don´t know the function of the first OpAmp circuit. What is the ...
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2answers
549 views

Significant error with unity-gain feedback op-amp

I used this OP97 op-amp to make a simple unity-gain feedback circuit. I would expect the output in this case to follow the input with very little error, however the output is actually measured at \$ 2....
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34 views

A few questions regarding the functionality of this negative peak audio detector

I have some queries regarding this peak detector from an audio compressor circuit: My understanding of the process is that when the positive input swings low, D5 is negatively biased and stops ...
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1answer
190 views

Help figuring out an op amp circuit with two loudspeaker outputs

I have to design a circuit that amplifies a sine wave with either a AD8616 or a LTC6256 (currently using the AD8616) to a 50 ohm loudspeaker and a rated power of 0.5 W. I'm a novice when it comes to ...
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1answer
46 views

Thevenin Equivalent of Common-Gate Amplifier

I'm having some difficulty understanding how Razavi determined \$V_{\text{in, eq}}\$. My understanding was that the small-signal model allows us to model the PMOS device as a constant current source (\...
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1answer
46 views

Blocking capacitor causing signal to go low in otherwise working amp/rectifier circuit

I'm making a simple amp > voltage doubler rectifier circuit to drive an lm3916 meter circuit and when simming to choose between JFET, BJT or OpAmp (just for my learning, I'm looking to a Jfet in ...
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2answers
49 views

Op-amp input voltage gets clipped off

I'm trying to build a simple voltage comparator using LM324N. Here is the circuit: simulate this circuit – Schematic created using CircuitLab The strange thing that happens is that after apply ...
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35 views

Inverting a (voltage-) transfer function using opamp

If we have a circuit that - given some input voltage \$U\$ - produces an output voltage \$f(U)\$ (where \$f\$ is continuous, monotonic descending), we can construct a new circuit that behaves like the ...
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87 views

Step up 3.3V to 5V to use as power of op-amp

In my previous question I was thinking about how can I "reuse" this circuit (0-10V, 0-20mA and digital contact input), when I only have 3.3V regulated power available from my LoRa Node: ...
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21 views

What is the equation for “beff”, i.e., “Gain Factor in Saturation” in BSIM4?

Using the device parameter list in Cadence, I found out that ID follows this equation exactly: ID = 1/2 * beff * vgt**2 I also found out that ...
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122 views

Don't understand this zero pole plot example

I'm reading a book (see figure 5-12) about (among other things) pole zero plots and there is an example I don't understand. For the schematics and formula below: it adds the following zero pole plots:...
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42 views

Maximum signal transmission from OPAMP output

I generate an analog voltage from PIC microcontroller output. I want to transmit this analog signal to maximum distance as much as possible using single wire. I have non-inverting OPAMP at the output ...
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3answers
72 views

Inverting Op Amp LM324

I am new to electrical design. I am experimenting with op-amps on LTspice, I cannot seem to figure out why my output signal is smaller than my input. I chose Rf to be 10k and Rin as 1k. The gain ...
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1answer
45 views

An Integrator Reset Circuit not working properly

I am trying to integrate the output of a Rogowski coil , with an inverting integrator with a reset circuit. I want to have the voltage level 0V during the off time of my switch, however after reset ...
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2answers
84 views

How can Gilbert Cell circuit provide linear gain variation even though ID-gm relationship is nonlinear?

How can Gilbert Cell circuit provide linear gain variation even though ID-gm relationship is nonlinear? As I undertstand it, the vcontrol (the voltage at the gate of M5 and M6) changes the biasing ...
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482 views

Analog input scaling before ADC sampling

I'm trying to read a voltage value from a chemical sensor. the sensor value can range from 0 to 7 volts. My microcontroller is running on 3.3V. I'm not allowed to consume current from the sensor so I ...
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1answer
51 views

Designing a non-inverting programmable gain amplifier circuit using the LT6910-1

I'm trying to design a band pass filter with a programmable gain option to record varying levels of sound as defined from a microcontroller. I used LTspice to design my circuit, and the filter portion ...
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1answer
63 views

3-Electrode sensor potentiostatic circuitry

I'm designing a circuit to read out the C2H4-CA10 sensor. Following the typical applications document, I designed the following: To verify the schematic, I created a new TINA simulation: When ...
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1answer
51 views

Custom Ultrasonic Sensor Schematic

I am trying to recreate this project. I have the circuit constructed on a breadboard. I am using an SP232 instead of a MAX232, a TIP42CG PNP instead of a BC557 PNP, and an Arduino Uno instead of an ...
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3answers
183 views

Operational amplifier output buffer

I made a simulation for a simple output buffer to use more current for an operational amplifier. The goal is to achieve a precise output voltage at moderate speed (This is considerd a DC application) ...
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1answer
36 views

Monoshot oscillator with a opamp level shifter gives huge oscillations

I am trying to level shift the output of a LTC6993-3 using a THS4631 based level shifter. I get a 0-5V output which I want to level shift from -5V to 0V. I get a clean output from the monoshot but, ...
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1answer
118 views

Analog input to ATMEGA328P using op-amp - how does this circuit work?

I was looking for a good solution in order to use a bunch of components and read 0-10V/0-20mA and digital inputs using my Arduino Pro Mini (ATMEGA328P working at 3.3V.) I've found online this ...
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2k views

How does this MOSFET/Op-Amp voltage regulator circuit actually work?

I am trying to understand the functioning of this circuit since I have read that it is appropriate for power regulation: Here is the explanation that I have found: The zener diode provides the ...
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42 views

How does high feedback resistor (gain) affect offset voltage or noise?

I wanted to get some insight on how high feedback resistor or high gain can affect offset voltage/ noise of an op-amp. I'm using 100M ohm as my feedback resistor for LMC6001, will it increase offset ...
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1answer
119 views

How to get the DC gain of an active high pass filter?

Edit: I think maybe I am confusing terms (it has been a few years since my last electronics class). I am trying to get the expression for the gain of this active filter amplifier circuit in terms of ...

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