# Questions tagged [diff-amp]

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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 ...
319 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 ...
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 ...
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 ...
1k 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 ...
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 ...
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 ...
209 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 ...
495 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 ...
492 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 ...
143 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 ...
457 views

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 ...
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 ...
138 views

### 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 ...
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 ...
469 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 ...
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 ...
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 ...
90 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? ...
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 ...
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 ...
271 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-...
244 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 ...
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 ...
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 ...
203 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 ...
1k views

### Create a differential output signal

I need to supply the galvo driver with a signal "Voltage Range Ā±3.0V p-p or Ā±10.0V p-p (Differential Input)" - that's what it says in the datasheet. I have a 0-5V single ended DAC and differential ...
112 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. ...
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= ...
85 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 ...
398 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 ...
461 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 (~...
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 ...
268 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?
893 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 ...
123 views

### Where do input bias currents flow and what voltage drops do they create?

I have asked this question (and answered it below) mainly as a continuation of the question, How does the compensation resistor in an inverting amplifier compensate for the input bias current?... but ...
682 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 ...
99 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 ...
141 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 ...
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 ...
602 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 (...
36 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'...
338 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 ...
587 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 ...
990 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 ...
222 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 ...
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 ...
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 ĪRs between the values of the resistances of the source brings a ...
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 ...