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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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 ...
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1 vote
2 answers
64 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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0 votes
3 answers
64 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?
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-1 votes
2 answers
50 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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  • 11
0 votes
2 answers
96 views

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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  • 195
4 votes
1 answer
214 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 ...
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5 votes
5 answers
372 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 ...
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2 votes
1 answer
61 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 ...
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1 vote
1 answer
55 views

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
45 views

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 ...
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1 vote
3 answers
134 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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0 votes
1 answer
71 views

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.
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3 votes
1 answer
46 views

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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0 votes
2 answers
120 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
58 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 ...
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2 votes
1 answer
104 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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1 vote
4 answers
237 views

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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  • 141
0 votes
1 answer
50 views

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 ...
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1 vote
3 answers
200 views

Differential amplifier using LM741

I am trying to build a differential amplifier using the lm741 op amp, and simulate it in LTSpice. The dynamic range of the output is too small (about 20mV), I use a rectangular wave (3.3V) and 1.8V DC ...
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1 vote
1 answer
147 views

How is the AC equivalent drawn?

Fig. (b) is the AC equivalent of Fig. (a). I am not sure if this is right. Why is \$r_e'\$ grounded?
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2 votes
0 answers
45 views

Why feed a V_OCM outpin pin of a FDA?

The Analog Devices reference design CN0540 (see diagram below) shows an AD7768-1 ADC together with a fully-differential ADC driver ADA4945-1. I am wondering why the common-mode voltage pin V_COM of ...
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  • 195
3 votes
5 answers
188 views

Measuring bidirectional voltage drop across current shunt on positive rail

I want to measure a voltage drop across a current sensing resistor (in both polarities) on rails up to 30V using an Arduino / AVR ADC with 1V1 reference. For background, this is a part of a battery ...
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  • 131
0 votes
1 answer
67 views

Diff amp ac equivalent circuit confusion

In the circuit below, base of Q2 is grounded. Even though base of Q2 is grounded in the circuit, the ac equivalent circuit(T model) seems to suggest that one end of the current source Q2 is also ...
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2 votes
1 answer
120 views

About Negative Gain in Bode Plot regarding the Op-amp Circuit Design and its Relationship with the Feedback Resistor

I am new to the circuit simulation and now I am using Tina to simulate a op-amp circuit for a photodetector. I have some questions regarding the bode plot. Below is the circuit design, based on the ...
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2 votes
1 answer
79 views

Understanding Summation of Currents in a Rail to Rail Differential Stage

In order to understand rail to rail OpAmps I consulted a (german) textbook. There, I found this principle schematics: So far I understood, there are two complementary differential input stages (T1, ...
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  • 361
1 vote
2 answers
246 views

MPX2100DP differential pressure sensor with Arduino

I am trying to use a pressure sensor which is MPX2100DP. Datasheet is; https://www.nxp.com/docs/en/data-sheet/MPX2100.pdf My goal is to measure the air pressure inside a pipe. First of all, I tried it ...
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  • 13
0 votes
2 answers
133 views

What is common-mode voltage in a differential amplifier?

I am using an LM2904 for my application. One of the input voltages, the voltage at the negative terminal of the op-amp (Vin-), can vary from -400mV to 500 mV. However, the voltage at the positive ...
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0 votes
0 answers
69 views

Fully Differential Amplifier With Common Mode Feedback Network

I need to design the following circuit in a way that can provide a gain of 1000 and also has a power dissipation of 1.8 mW which, according to my calculations, results in a branch current of 250 μA. I'...
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  • 28
0 votes
1 answer
104 views

How does this offset and gain amplifier work

The circuit below is meant to scale and offset Vin to Vout: In the actual application Vin is a battery voltage (4 to 5.5V ish) and Vref is a fixed regulated voltage derived from it (3.3V). The op-...
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  • 103
0 votes
1 answer
92 views

voltage divider inside differential op amp configuration

I'm working on a DIY analog synth based on the CEM3340 chip. When feeding it 12V at VCC it will output waves at different amplitudes that I'll want to scale to 5V to -5V: Square: 0-10.7V Sawtooth: 0-...
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3 votes
2 answers
464 views

Why does differential op-amp require mid-point biasing at its input to prevent clipping?

There's an AC signal, 1 V amplitude, which is the input to an op-amp, in differential mode: However, the output gets clipped and the amplitude isn't unity for some reason, even though gain is set to ...
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1 vote
1 answer
63 views

Voltage gain of a differential amplifier with tail resistor

Suppose the following differential amplifier: simulate this circuit – Schematic created using CircuitLab To calculate the differential gain, I take advantage of node P being an AC ground and I ...
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0 votes
1 answer
66 views

Problem amplifying differential signal from DAC

I encountered a problem while designing my own waveform generator. In my design, I am using a DAC (DAC5662) to generate different types of signals, and then I amplify the signal using an operational ...
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1 vote
1 answer
100 views

Why is the output impedance so high in my differential op-amp?

I tried to make a differential op-amp, but I get around 65k ohm of output impedance. I read online that op-amps should have ~50ohm to about maximum ~500ohm output impedance, but however I change ...
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-1 votes
1 answer
66 views

Gain Value For Modified Differential Amplifier Circuit

I am trying to analyze the following differential amplifier circuit and am wondering how to calculate overall gain (it will be fed with two copies of the same audio waveform 180 degrees out of phase ...
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4 votes
1 answer
197 views

Controlling gain and modulation depth of long-tail pair as AM modulator?

I'm investigating use of a differential pair as an AM modulator. The schematic below illustrates the general plan, but the values aren't really specific (not least because this isn't working yet!) ...
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3 votes
1 answer
86 views

How should the differential gain of an op-amp be interpreted?

Let us consider an open-loop op-amp circuit: The output voltage including the common mode signal is given by: $$ \mathbf{v}_{\mathbf{o}}=\mathbf{A}_{\mathbf{d}} \mathbf{v}_{\mathbf{d}}+\mathbf{A}_{\...
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1 vote
2 answers
255 views

What do the PNP transistors in a 741 differential pair do?

I am working on a project using the internal circuitry of LM741 op-amp and I've found its differential pair quite interesting. Mostly its NPN to PNP input. I've searched it to see what it does but ...
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0 votes
3 answers
186 views

Is it okay to connect two differential amplifiers in parallel from the same signal source?

I have a current sense resistor of 0.0025 ohms where I want to connect to two differential amplifiers in parallel. I want to know if it is okay to use multiple differential amplifiers connected to the ...
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0 votes
0 answers
159 views

Increase input impedance of differential voltage amplifier without op amp?

For fun, I'm working on an audio project which calls for a differential voltage amplifier - something I don't have experience with yet. The circuit below is no good, because the differential amplifier ...
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0 votes
1 answer
87 views

How do you analyze this simple circuit? [closed]

I want to plot Vout vs time graph (which software do you suggest) and also want to find out max and min output voltage (Vout) of the circuit. How can I find the max and min manually? Can I find them ...
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  • 11
1 vote
3 answers
341 views

Common mode impedance in operational amplifier

While looking at this simulation, as they say no current flows at the non inverting terminal of the op-amp, but looking at the differential stage of the operational amplifier shouldn't there be some ...
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  • 699
0 votes
1 answer
55 views

Potential In VA

I'm trying to find VA and I don't get something, is Ic1 = V+/20k, and then this current splits through emitters of Q1 and Q2? If so, then the voltage VA is 0? Also, I know that Q3 and Q4 are a ...
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  • 107
3 votes
3 answers
176 views

Confusion about differential amplifier configuration

As in the picture shows the signal applied at the base is say 1mv p-p, the circuit bias is not provided, then how this 1mv p-p able to forward bias the B-E junction?
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  • 699
0 votes
2 answers
172 views

negative voltage of a differential amplifier

Can somebody explain what is this negative voltage -VEE in the circuit? I thought two parallel circuits are connected to the power supply vcc, but how this VEE came? Can somebody explain me this using ...
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2 votes
1 answer
40 views

Why is Q1 taken as 'on' and Q2 as 'off' in the differential amplifier?

The book tells that we can arrive at the conclusion by reasoning. Why can the voltage at the emitter not be -0.7 V so that both the transistors would be on?
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0 votes
1 answer
135 views

How to calculate the collector and emitter resistors in a differential amplifier with transistors

I'm refreshing my electronics knowledge a bit (after 30+ years), and I'm trying to build an audio amplifier from scratch without integrated circuits (transistors, and mosfets only). I'm trying to ...
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0 votes
0 answers
94 views

Finite CMRR even with ideal tail current source (body effect)

In Razavi's Design of Analog CMOS Integrated Circuits 2nd edition page 123, the diff-pair below is included with a comment about how even if the tail current source is infinite, if the transistor pair ...
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  • 499
1 vote
1 answer
543 views

Using LTspice to simulate common-mode signal interference in a differential amplifier?

I'm experimenting with differential amplifiers, and I'm trying to simulate some ways that the common-mode rejection ratio of a DA in the real-world would be decreased. (In other words, ways to ...
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  • 133
2 votes
0 answers
626 views

How to measure Common Mode Range and Output Swing of a CMOS Differential Amplifier in LTspice

I'm designing a CMOS opamp in LTspice here is my current design. The amplifier obtains a DC gain of roughly 50dB and has a phase margin of 70 degrees at a ω (unity gain frequency) = 250 MHz. I'm also ...
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