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).

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Differential amplifier input/output simulation

I'm trying to understand how to simulate the schematic proposed on page 9 (Figure 12, circuit for audio ADCs with balanced inputs) of the THAT 1280 series datasheet: THAT1280/THAT1283/THAT1286 The ...
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1 answer
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Differential amplifier current source problem

I got this question on my exam: Assume the two input voltages \$v^+\$ and \$v^-\$ are equal such that \$v^+=v^-=v\$, and the two transistors Q1 and Q2 are identical. What is the lowest value for \$v\$ ...
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Calculating CMRR for a Long-Tailed Pair in LTSpice

I am trying to understand the behaviour of Long-Tailed Pair amplifiers and have been given the following simulation circuit (The PMOS models have all parameters defined): Firstly, I am generating a ...
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2 answers
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Is `c` or `t` the positive line of a differential pair?

I'm looking at the W66CP2NQUAFJ from Winbond. It has a couple of pins, namely CK_t_A and CK_c_A. In the datasheet, it says that ...
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1 answer
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Parallel resistances in 'C' configuration

If we have three resistors, two resistors on two separate nets with a third resistor connecting these two branches together, how do you calculate their total resistance? I thought the three ...
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2 answers
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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 ...
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4 votes
2 answers
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What is the difference between these differential amplifier circuits?

Why are there two collector resistors in the first circuit but in the second circuit there is only one? What is the difference? When there is only one collector resistor, does this affect behavior?
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1 answer
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MOSFET differential amplifier

I have two questions about this circuit. As operating points, Vds=(Vdd-Ir*Rd)-(-Vgs). I do not understand why we put -Vgs. The second question is, if we take only one output (Vo1) what would Acm (...
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6 answers
584 views

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 ...
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How to size a differential amplifier for minimal offset?

What is the strategy for optimizing the offset of the differential amplifier in addition to increasing the size of the cross-coupled transistors? Are there any sizing rules to follow to size the ...
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1 answer
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Symmetric path for analog inputs into an ADC

I am designing a PCB based on the ADS1299 chip from TI, which is essentially an ADC with amps and some other functionalities. I have seen a lot of emphasis on differential inputs into an amplifier to ...
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RC differentiator / RC integrator explanation (input waveform is square wave, triangular wave, sine wave)

The circuit below is an RC differentiator (RC high pass filter.) The input and output waveforms: I can understand this. Mainly due to capictor charging and discharging. How about an RC integrator (...
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Best way to implement bypass circuitry for analog crossover filter circuit?

Below is a system block diagram of a schematic / PCB I am working on. It is an SOC with two differential audio DACs (left and right audio channel). Each channel has a fully differential cross-over ...
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2 answers
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Differential amplifier with active load current mismatch

From: Design of Analog CMOS Integrated Circuits by Behzad Razavi The author mentions in Fig 5.26(c) that if a positive change is applied to the gate of M1 and an equal and opposite change is applied ...
3 votes
1 answer
63 views

How does the offset correction work in this circuit?

I'm reading a paper about a received signal strength indicator (RSSI) amplifier. The amplifier was to estimate the relative power of the input signal, and was designed by cascading 6 limiting ...
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2 answers
178 views

Differential pair with source degeneration

[Design of Analog CMOS Integrated Circuits by Razavi] The author introduces a differential pair with source degenration which helps 'soften' the Vin/Vout characteristics of a differential pair: He ...
2 votes
2 answers
231 views

Need help solving a differential amplifier circuit

I've been trying to solve the circuit below for hours now but to no avail. I can't figure out what to do. I've been given a single input, unbalanced output differential amplifier circuit to solve for ...
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1 answer
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Arduino EMG with 5000 Hz Nyquist sampling

I need to build an EMG using Arduino that can detect up to 2000 Hz (instead of just up to 250 Hz) so the sampling needs to be at least 5000 Hz (to satisfy Nyquist theorem). I want to focus on the ...
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1 vote
1 answer
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Difference amplifier relation between Vout and Vin

For this question I have to give the relationship between Vout and Vin. I already have the answer, but I just do not know how I should get there exactly. The circuit looks like the following: To me ...
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Linearity in Differential Amplifier

Trying to understand what is the maximum and minimum for the input signal of a differential pair by solving this example below. My solution: To let the circuit operate as a differential pair, it must ...
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2 answers
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How does this EEG chip compare to modern EEG (is it still used now)? [closed]

I got from my drawer last night a vintage Brainmaster 2E I bought late 1990s that I used only a few times during that period. It has serial port at back. My question concerns the gain of the amplifier ...
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3 answers
164 views

How is DC bias offset removed in a differential amplifier circuit?

Looking at the long-tailed pair, if we remove the dual supply and bias the amplifier for single supply operation it will generate a DC-shifted signal. How is this DC-offset typically cancelled for ...
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1 vote
1 answer
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Differential amplifier with ideal current source and resistive loads

In this circuit, I want to find how each node's voltage changes as Vin changes. My approach is as follows: The total current is 2·I. The current in R is fixed and equal to I which implies that Vo2 is ...
2 votes
3 answers
503 views

Differential pair with active load including resistance

In solving the differential pair with an active load, I am able to find the gain without including R1 as shown in the figure. When R1 is included, I am stuck on how to proceed. Could you help me out? ...
1 vote
1 answer
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Differential and single ended crosstalk and clearance

I know that there can be crosstalk between differential pairs (and you need at least a few lengths equal to the diff pair between diff pairs, usually 3 or more diff pair widths). What is the ...
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4 votes
3 answers
187 views

Interfacing a unipolar 0-5 V output with a bipolar +/- 0.1 V DAQ system using a differential amplifier and voltage divider

I need to connect a sensor system that outputs 0–5 VDC to a data-acquisition system (DAQ) that accepts inputs of ±0.1 VDC (it is designed for a different type of sensor, but I need to repurpose it in ...
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1 answer
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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 ...
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1 answer
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Differential amplifier with gain < 1

I have a differential signal ±6 V (12 V differential) that I need to condition for an ADC (AD7124) with a 4.096 V reference voltage. Signals of interest are DC-20 kHz. I can make the circuit below ...
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What's the difference between dynamic comparator and improved latch-type sense amplifier in a flash ADC?

I know about flash ADCs that use comparators or sense amplifiers as in the pictures. What's the difference here? They seem different, as they have some different type of sensing sequence, and it looks ...
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1 answer
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What is wrong with this MOSFET differential pair analysis?

I am confused regarding the analysis of the circuit on the left and its small-signal equivalent circuit on the right: simulate this circuit – Schematic created using CircuitLab Here is my ...
2 votes
1 answer
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How to verify noise modelling in fully differential op-amp Spice models?

Texas Instruments explains in one of their videos how to verify the noise model of op-amps in Tina-TI. T For this, the op-amp is wired in a buffer configuration. A voltmeter (voltage pin) is placed at ...
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1 answer
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Questions on Vss for op-amps (differential amplifier)

I was working on a voltage amplifier and confronted the following problem regarding Vss of the op-amps. The op-amps I am using are MCP603T-I/Ps. The circuit diagram is as shown below. (INSTRUMENTATION ...
2 votes
3 answers
108 views

How does a BJT differential amplifier amplify?

I am reading The Art of Electronics. I found a related question here. I understand that differential gain of the amplifier is $$G_{\text{diff}}=\frac{R_c}{2(r'+R_e)}$$ but how? OK, using hybrid-pi ...
1 vote
2 answers
134 views

Benefit of fully differential amplifier

I am trying to build an audio amplifier PCB with S/PDIF and single ended line level inputs and want to use the CS42528 CODEC (datasheet). My questions are regarding the input and output stages of this ...
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3 answers
81 views

What type of op-amp configuration is this from a PLL circuit?

Can someone help me to understand this attached op-amp model? We are using it in an HMC3716 PLL circuit. We don't know how it works, exactly. Is it an integrator or a differentiator?
-1 votes
2 answers
81 views

What is the voltage range on ADC's inputs? Photodiode + TIA + ADC

Can someone here help me understand this circuit better? It's a photodiode -> transimpedance amplifier (TIA) -> ADC. What is the voltage range on the ADC's inputs? AIN- and AIN+. Which input is ...
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2 answers
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LM139 equivalent circuit

Follow up to the follow-up question. I am close to my goal to be able to restore the sound circuitry of the arcade game in question. One of my plans was to emulate the comparator circuitry with ...
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4 votes
1 answer
293 views

How to implement unity gain buffer with long-tailed pair?

I read that a unity gain buffer can be implemented with an op-amp like in this circuit: I also read that a long-tailed pair as an op-amp (this might be the wrong part). So according to the buffer ...
5 votes
5 answers
394 views

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 ...
2 votes
1 answer
244 views

Real input range of differential ADC HX710B

Accordingly to the datasheet of HX710B its differential input range is +/-20mV. The HX710B is used in the air pressure sensor together with sensing bridge MPS20N0040D. The schematics is: For reading ...
1 vote
1 answer
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Pressure Transducer, Reverse and Shift Output of a differential amplifier

I am making a custom hydraulic brake for my sim racing setup. The original brake uses a potentiometer which outputs 3.3V at no brake pressure and 0V at full brake pressure. My pressure transducer, ...
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1 vote
1 answer
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Feedback loop gain not as expected in a differential amplifier

I am trying to build an approximate opamp with a differential amplifier and add a feedback loop to get the approximate wanted gain. I used a differential amplifier with a current source and a current ...
1 vote
3 answers
135 views

How can I go about understanding an electronic circuit?

I have this circuit: My goal is to gain a qualitative understanding of what VO1 and VO2 are going to look like for different signals V3 and V4 applied. Because you can not calculate with BJTs or ...
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1 answer
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Calculating Rin of a differential amplifier

I have this circuit: I want to find the input impedance \$R_in\$ with a PSPICE simulation. I'm not sure how to go about this.
3 votes
1 answer
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Voltage variation in the output of Differential Amplifier

I am working in low side current sensing differential amplifier circuit. VA is connected to ground and resistance R2 is also connected to ground but both the grounds are not same then there is voltage ...
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2 answers
122 views

Does anyone know why this diff amp isn't working?

simulate this circuit – Schematic created using CircuitLab I'm new to electronics and I've been figuring out how a diff amp works. I followed a schematic I found on YouTube. Basically, as V3 ...
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0 votes
1 answer
120 views

What is the input capacitance of a differential pair?

For part (c) of this problem, I am not sure how the input capacitance is defined for a differential pair since we have two inputs. Would I have to find two different input capacitances (one for ...
2 votes
1 answer
171 views

Unity gain differential amplifier null adjustment circuit not working

I have a differential op amp that I believe I have set up as a unity gain differential amplifier. When I measure the potential difference across pin 6 and ground and adjust the 5K trimmer ...
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4 answers
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Input impedance for a difference amplifier OpAmp circuit

For the above circuit, I would like to find the input impedance for the input \$v_1\$. Assuming that \$R_1 = R_2\$ and \$ R_3 = R_4\$, then: $$v_0 = \frac{R_3}{R_1} (v_2 - v_1)$$ As far as I know, the ...
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Differential multi-feedback band-pass filter design

I am trying to design a multi-feedback differential band-pass filter. While doing calculations I just took Texas Instr. design guides, but nowhere is mentioned exactly how to realize the filter for ...