Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [differential-amplifier]

For questions about circuits that amplify the difference between two input signals but not the signal common to the two inputs (e.g. the long-tailed pair). Do not use for questions about operational amplifiers (which are a type of difference amplifier) unless the op amp is used as a differential amplifier -- use only the "operational-amplifier" tag for most questions about op amps (e.g. an op amp as an inverting amplifier).

For questions about circuits that amplify the difference between two input signals but not the signal common to the two inputs (e.g. the long-tailed pair or op amp differential amplifier). Do not use for questions about operational amplifiers (which are a type of differential amplifier) unless the op amp is used as a differential amplifier -- use only for most questions about op amps (e.g. an op amp as an inverting amplifier).

243 questions
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How does an op-amp know where ground is?

Although I've been working with op-amps for a while, the following question never occurred to me before today. Consider first the op amp on the left (A). The negative terminal is connected to ground, and a small voltage \$V_d\$ is applied between…
MGA
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Inverting op-amp problem

Down below is an inverting op-amp circuit with a capacitor C connected to the non-inverting input. I have to find the voltage at point A and express it using vin, C and R. I tried to solve the problem using nodal voltage analysis: (vin - va)/R =…
kauselis3000
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Why are two stages used for an instrumentation amplifier?

When we have a two-stage instrumentation amplifier, such as the following. Why do we need the first stage of the two Operational Amplifiers? Couldn't we just input V1 and V2 into the differential amplifier?
Bee
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Another Failed Differential Amplifier

This is the circuit I made - designed it, calculated it, built it: simulate this circuit – Schematic created using CircuitLab Q1's and Q2's collector current was 5mA, while Q3's was 1mA. Sine wave at the input had 1Vpp at 1kHz. Negative feedback…
Keno
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How can there even be an input voltage on a long-tailed pair?

Assuming the following: The voltage across the base-emitter junction of a BJT is constant in forward-active and saturation mode The BJTs in a long-tailed pair are normally forward-active or saturated (If any of these assumptions are incorrect,…
nc404
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Calculate differential amplifier's input impedance

How does one calculate the input impedance of a differential amplifier? Since the input impedance of an op-amp is very high, the input impedance for V2 should be R2 + Rg. But what would be the input impedance for V1?
zud
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My RF amplifier circuit works in LTSpice. Will it work in reality, too?

I am working now for a while with bias calculations. I have found a good turorial to calculate it by my own and I have seen that there are already calculators on internet, which made my life much easier than i supposed to manage. I have now a…
lastime
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Why would a Diff Amp require both inputs to have a DC path to GND to work?

I'm looking at using a NI PXI-6255 DAQ card and I noticed in the manual it says "Both inputs of the (diff amp) require a DC path to ground in order for the (diff amp) to work." Is this a common design constraint to use a differential amplifier? If…
SiegeX
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Op-amps with negative feedback and differential amplifiers. What's the difference?

I'm a physicist attempting electronics - so please bear with me. I feel I am missing something very very obvious. simulate this circuit – Schematic created using CircuitLab An op-amp with some negative feedback (as I've drawn) will attempt to keep…
Tomi
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Output voltage for operational amplifier goes to supply rails

I've been trying to understand the innards of an op amp and I'm having a hard time understanding why the output looked clipped. Below is the schematic I got from Hackaday. I've simulated this in LTSpice. Here is the input(SINE source, green line)…
hellowurf
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What is this schematic symbol in the INA851 overvoltage schematic?

I was looking at the INA851 and trying to understand the input over-voltage protection. I can't seem to figure out what this pictured part is.
Tzanker
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Why does Q1 turn on and Q2 turn off when I apply 5 V?

Differential amplifier circuit below: When the inverting input is floating and the non-inverting input is grounded Q1 turns off and Q2 turns on. This part I understand; V2 is supplied to Q2's BE junction (V2 >> ground >> Q2 BE junction >> Q3 CE…
Heroz
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Instrumentation amplifier cross-connection circuit

I am trying to implement a circuit from an ADI app note that I have not seen anywhere else : Here it is in PDF format which is a copy of this article. I strongly encourage reading it as it is quite short and interesting, providing much more insight…
Ryan
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Why does this op amp input stage have single ended output?

Looking at the internal diagram of LM324: I see that the output of the the input stage, which is a differential pair, is single ended rather than being a differential output. How does then this input stage block common mode signals? As I understand…
Jonathan Wick
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Can we explain the differential pair in terms of resistances?

It has always been a big challenge for me to find the most general ideas behind great circuit solutions that can be illustrated by simple electrical concepts... and even by non-electrical analogies from our daily lives. The differential…
Circuit fantasist
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