Questions tagged [diff-amp]

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12
votes
5answers
2k views

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 ...
10
votes
2answers
311 views

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 ...
7
votes
2answers
2k views

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 ...
6
votes
1answer
29k views

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 ...
5
votes
1answer
983 views

Why is my op-amp chopping up my signal?

I have built an instrumentation amplifier out of two op-amps in a quad op amp (MCP6L04T). The input signal is coming from a low-impedanece source (~17k) and most of the information in that signal is ...
4
votes
3answers
2k views

Differential Amplifier Biasing Problems

This is the circuit that I built: (desired voltage levels are described next to the circuit) simulate this circuit – Schematic created using CircuitLab I tried to make proper bias conditions ...
4
votes
3answers
5k views

Is it possible to make a non-inverting difference amplifier?

For a crude current sense application I am wondering whether it is possible to build a non-inverting difference amplifier without common mode offset on the output. Reason: I would like to avoid ...
4
votes
2answers
206 views

What step have I missed designing this differential amplifier?

First time posting on EE.SE and I hope this question isn't too broad. This will be a long post. I should also point out: I'm asking the process and not the solution the problem. I've did create a ...
4
votes
1answer
479 views

Why modern oscilloscopes inputs are not fully differential (i.e. floating)?

This question is somewhat related to this other EE.SE question, and some hints are given there, but are not completely satisfactory for me. I've understood that, besides safety considerations, the ...
3
votes
4answers
488 views

Differential Amplifier's Unusual Behavior

This circuit is made of one differential BJT transistor pair and voltage-amplification stage with negative feedback. simulate this circuit – Schematic created using CircuitLab About this ...
3
votes
2answers
141 views

Why need to separate the path of the current of these two signal source?

This is a differential amplifier with common-mode signal as input (figure a) : Since equal voltages vin(CM) drive both inputs simultaneously, there is almost no current through the wire between the ...
3
votes
3answers
439 views

A question about remote ground sensing and its advantages

In this article, they are explaining the benefit of using a technique called remote ground sensing by using a single-ended sensor and a differential amplifier or an instrumentation amplifier. Below is ...
3
votes
2answers
111 views

OpAmp: Calculating A - MAX(B, 2V)

I require an opamp-based circuit that calculates the expression OUT = A - max(B, 2V), as shown here: There are no strict requirements on the shape or exact position of the transition, however in the ...
3
votes
2answers
2k views

What causes the common mode gain in MOS differential amplifier

I went through many of the past questions in this forum and also a lot of other sites but none answered my question, so I made up my mind to post it here. What exactly causes the common mode signal ...
2
votes
2answers
463 views

Why are these instrumentation amplifier circuits equivalent?

I am confused about the circuit of an instrumentation amplifier. In class we solved the following example: simulate this circuit – Schematic created using CircuitLab No big deal; with negative ...
2
votes
3answers
4k views

How is a common mode signal generated in a differential amplifier?

I searched for information about common mode signals but I only got a vague idea about it, such as it is a noise signal generated between input signal and common ground. However, I do not understand ...
2
votes
1answer
2k views

High side current monitor to measure microamps

I am trying to sense very low current (50 - 200 uA) on the high side of a circuit, and was considering LTC6102HV for the job since it can be "floated" to 105 V. My problem however is that my circuit ...
2
votes
1answer
89 views

What does an impedance to a fixed potential mean?

I am reviewing about differential pair and this comes up a bit confusing. Could anyone explain the part "equal impedances to a fixed potential" here? What does an impedance to a fixed potential mean? ...
2
votes
1answer
1k views

Single supply differential amplifier

I am wondering is it possible to design a differential (or instrumentation) amplifier that will operate from single supply? I have a 2Vp-p and 0.2Vp-p sine wave signals that need to go thru the ...
2
votes
1answer
4k views

What's wrong with this circuit to convert 0-5V to +10/-10V

I'm trying to come up with a solution to use the analog output of a DAC to drive the X-Y axis control of a commercially available laser 'closed-loop moving magnet' driver. I found an explanation on ...
2
votes
1answer
262 views

Fully differential amplifier - adder?

I have two signal sources providing the same differential audio signal (VIN1 and VIN2). I want to sum those signals. The result (VOUT) shall also be differential. The idea is to take a fully-...
2
votes
2answers
239 views

Differential Amplifier with Large Capacitive Load

I am experimenting with the following mixer circuit for audio: EDIT: SCHEMATIC FIXED All of the subcircuits work fine separately but when the diff amps are combined with the summer circuit, the ...
2
votes
1answer
3k views

Differential-output op-amp vs. additional inverting op-amp?

I'm wondering what the real advantages of op-amps with differential outputs are (e.g., AD8138), compared to just taking a signal V+ and feeding it to a unity-gain inverting amplifier to obtain a ...
2
votes
1answer
3k views

LM324 Difference / Instrmentation Amp 1mV Signals

I need to amplify 1mV signal from a wheatstone bridge (no DS available). 5kg max weight; output is 1mV/Kg @ 5V. The resistances are 880+880 and 749+749. Currently I only have LM324 and LM358. And ...
2
votes
2answers
202 views

What is the closed-loop bandwidth of the INA143 at gain 0.1?

The INA143 difference amplifier datasheet states that the device supports G=10 and G=0.1 when connected in difference amplifier configuration. However, the datasheet only gives specifications for the ...
2
votes
1answer
1k views

Create a differential output signal

I need to supply the galvo driver with a signal "Voltage Range ±3.0V p-p or ±10.0V p-p (Differential Input)" - that's what it says in the datasheet. I have a 0-5V single ended DAC and differential ...
2
votes
2answers
107 views

How to analysis this Operational-Amplifier circuit?

This is a reference buffer circuit that make a single-end audio input to be the differential inputs for ADC. Circuit-1: It does not like typical Op-Amp circuit of the same purpose like below. ...
2
votes
2answers
2k views

Op Amp CMRR problem

I'm studying on my own for an exam. I bumped into this problem that really got me. My answer just doesn't match. Find the CMRR of the operational amplifier above, consider Ad = 1000000 (Answer CMRR= ...
2
votes
0answers
78 views

Relationship between base resistor and collector current in this unbalanced differential amplifier

For this BJT circuit, I was wondering if there was a solution for how the collector currents change with respect to the value of the single base resistor. This arrangement popped up in a circuit I ...
1
vote
1answer
393 views

Transfer function of a LM380 power amp

This is an exam question. Our professor has some generator of tests and out of the blue this beast came. We couldn't ask for the clarification, being an exam question, but from what I can see it ...
1
vote
2answers
454 views

NPN Differential Pair - Emitter Voltage Variation

My understanding of how this circuit should work is : DC: The transistor bases are at about 0V DC due to R5 and R6. Some base current flows due to the constant current bias, so there is a small (~...
1
vote
1answer
3k views

how to resolve LM358's huge error as a current sense differential amplifier

I've built a current sense differential amplifier that measures the voltage across a 1 Ohm resistor, to give me a reading for the current through it. I've connected it as follows, all resistors are ...
1
vote
1answer
261 views

Two diodes in input stage of power amplifier

Some of the power amplifier schematics include diodes in input stage like below. What is the purpose of them?
1
vote
2answers
857 views

Differential Amplifier Transistor Pair

I have been dealing with these differential amplifiers for weeks now and still don't understand the basic principles of its operation and how should it be used inside an audio amplifier. I understand ...
1
vote
3answers
679 views

Subtracting Audio Signal from Ambient Noise Signal

So I'm pretty well-versed in the software world, and my buddy and I decided to tackle a hack idea to get into hardware hacking but we're trying to figure out whether our implementation will actually ...
1
vote
1answer
94 views

BJT differential amplifier

Is there any reason why the gain of a single ended input BJT differential amplifier, with one Rc, is a good approximation of the value of Adm for a common mode input. The simulation shows the ...
1
vote
1answer
136 views

Common Mode and differential Mode gain of this Cmos diff Amp inverter

This is one of questions our prof gave to students in recent years and im preparing myself for this exam. What is Common Mode and differential Mode gain of this Cmos diff Amp inverter? i understand ...
1
vote
1answer
162 views

Differential Amplifier Input Line-Level Signaling

This is the circuit I'm referring to: This stage is often used as input stage of audio amplifier. I am wondering, how can the input signal be normally amplified since there is no DC bias across the ...
1
vote
1answer
595 views

Single input impedance of long-tailed pair

I have following circuit: and I'd like to know input resistance of single input Ui. I tried to calculate it like this: if I increase Ui by little, there's some voltage drop on base-emitter junction (...
1
vote
1answer
32 views

MOSFET Differential Amplifier Bode Plot

I've created a MOSFET Differential Amplifier in PSpice, the schematic of which I've attached. However, when doing an AC sweep and adding a trace to do a Bode plot, the graph is a flat line, and I don'...
1
vote
1answer
328 views

Output voltage of MOSFET differential pair with current mirror load

I've seen this circuit from https://www.allaboutcircuits.com/technical-articles/advantages-of-the-actively-loaded-mosfet-differential-pair/ How are the drain voltages equal?? I can't seem to figure ...
1
vote
1answer
561 views

Differentiator (Op amp) with a square wave

I'm working on a differentiator (op amp) with a unitary gain i calculated the value of RC and the period with a frequency of (1kHz). Figure 1. Differentiator Schematic (OrCAD). This is the schematic ...
1
vote
1answer
980 views

Deriving Differential Mode Gain of an Op Amp

I have been looking all over for derivations of the expression for the differential mode gain of a simple single op-amp differential amplifier. One thing that I have found very interesting is that ...
1
vote
2answers
217 views

T-Feedback Circuit Vo/Vi (Why is my approach wrong)?

Here's what I did. I know it's wrong but I cannot figure out why. Let \$V_s\$ be the voltage at the node between R2, R3 and R4. From the ground to \$V_o\$ terminal there is a voltage \$V_o\$ which ...
1
vote
1answer
147 views

Why does an diff-amp being fed by two separate op-amps with low input resistances distort the signal on the inverting input?

I'm using the following circuit. In1 and In2 come from two separate amplifiers (Max9643), both of which are fed by a square pulse but have their inverting and non-inverting terminals criss-crossed ...
1
vote
1answer
65 views

How do I connect these two parts of solution?

A differential amplifier is fed in a balanced way with the source resistance Rs which is in series with each base.Show that a mismatch ΔRs between the values of the resistances of the source brings a ...
1
vote
1answer
1k views

2/4 Wire Conversion Circuit For UK Telephone

I am currently trying to build an op-amp circuit which allows seperation of send and recieve signals from the UK telephone line (or a simulation of the telephone line). I am having difficulty ...
1
vote
1answer
2k views

Gain on a Differential Amplifier

For the past hour, I've been trying to calculate the gain of a differential amplifier in the following form: \$ \frac{V_{out}}{V_{in}} = \$ some function of resistors I went to this site and tried to ...
1
vote
2answers
4k views

Differential voltage measurement at high voltages

I'm trying to measure a differential voltage. There are two ranges of measurement, one from 0-5V and the other from 0-50V (the reason for different ranges is to get a higher ADC resolution in the ...
1
vote
0answers
39 views

Rectified DC current measurement using shunt or Current Transformer

I am working on a project to design a controller for battery charging solution. A 3 Phase delta power (440 Vrms ph to ph) is given to a 3-phase Variac Transformer ( Variac is operated ...