Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers, which are DC-coupled high-gain electronic voltage amplifiers with a differential input and, usually, a single-ended output.

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Splitting a 50 Ω pulse signal into two gain stages

Given a pulse from a charge-sensitive preamplifier with 50 Ω, output impedance I'd like to split the signal into two separate conditioning circuits. Using an AD8009 as a buffer I've come up with this ...
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3 votes
4 answers
410 views

Is an op-amp's output current limited by the supply (+/- Vsupply)?

As above. I'm looking at the OPA548. The max. output current is 3 A, but reading the datasheet, I'm unsure if that's from the +/- Vin or the +/- Vsupply.
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2 answers
84 views

Input impedance of op-amp

How can I calculate the input impedance of this circuit?
1 vote
3 answers
96 views

TL072 weird output when used as buffer

Dear all, I tried to use TL072CP op amp as a buffer, however to my surprise it outputs a perfect triangular wave with reduced amplitude when given sine wave input of 150kHz and I have used a 12V and -...
1 vote
3 answers
82 views

What is the source of noise in this AD620/OP490 EEG circuit?

The circuit diagram came from the Brainmaster 2E EEG above. Their latest software I downloaded in their website bricked the EEPROM memory. Their Support refused to give me the firmware or fix and said ...
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2 votes
1 answer
124 views

How to buffer an AM signal?

The above shows an AM modulator circuit which sums a sine wave and a triangle wave to produce an output which will undergo resonance using RLC to produce an AM signal. The TL072 is commonly used in AM ...
2 votes
1 answer
85 views

Why make second stage current larger than input stage current in op-amp?

When people speak about the slew-rate of a Miller-compensated op-amp, the usual derivation is that the slew rate is approximately the input tail current divided by the Miller capacitance. E.g. here (...
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2 answers
120 views

Why is one op-amp in my circuit messing up the other?

I am attempting to create a board that takes an input signal, outputs the buffered input signal and its inverse, and then also outputs the difference of those signals once affected by an outside ...
1 vote
1 answer
53 views

Finding poles by inspection - 2 resistors

This is a follow on question from Finding poles by inspection - R to ground Is this correct? I have tried to follow the approach there.
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2 votes
3 answers
87 views

3 dB frequency of first-order active high-pass filter

Using the KCL law in the red dot in the circuit shown above, I got this equation: $$\frac{V_\text{in}}{R_1 + \frac{1}{j\omega C}} + \frac{V_\text{out}}{R_2} = 0$$ From this equation the transfer ...
1 vote
3 answers
75 views

Current flow in non-inverting op-amp amplifier

How does the current flow in this particular circuit? I know that \$R_3\$ isn't important as there is no current flow (ideal op-amp). I want to calculate the different currents with Kirchhoff's ...
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3 answers
40 views

Biasing a low AC voltage for input to an ADS1115 ADC

I have an AC signal from a position sensor that changes between -200 mV and 200 mV, something like 400mV peak-to-peak. I have ordered an ADS1115 breadboard and I use an STM32 microcontroller. I'm not ...
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2 votes
3 answers
125 views

Can noise back-feed through an op-amp?

Take a non-inverting op-amp, where the output is connected directly (0 Ω) to the inverting input. If noise from EMI exists on the output, would it be possible for the noise to be seen on the non-...
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34 views

Potentiostat calibration and measurement

Maybe this question is obvious, but I'll try. I am trying replicate this potentiostat without R5: In the interests of calibrating it I've joined the reference and the counter electrode to resistor of ...
1 vote
1 answer
37 views

Is it possible to get an estimate of the power consumption of a circuit by modeling it with controlled sources?

Let's say I have an op-amp. We can measure the power consumption of the circuit by multiplying the current supplied by the voltage supply with the voltage of the voltage supply. Now, suppose this op-...
2 votes
1 answer
48 views

Input noise of ADC AD7768 with opamp driver ADA4945-1

I'm operating an ADC AD7768 with an opamp driver ADA4945-1. I measured the noise for three different cases: Both differential inputs open/floating Both differential inputs connected to AGND Both ...
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Analog step sequencer schematic help

I'm currently working on an analog step sequencer for a synthesizer I'm making. It has a split rail 24 V supply (so +12V, GND, -12V) and follows the Kosmo specification. The features I want are: 8 ...
1 vote
1 answer
31 views

Determining combination of resistors for an equivalent time constant in an integrator circuit

I have a varying source voltage for maximum of 15 V and am using an error amplifier to maintain it using an integrator. Reference voltage is of 5V. I want a time constant of 100 msec with a capacitor ...
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1 answer
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Op-amp with capacitor showing output voltage of 2.98 V despite 0 input voltage

I am having trouble with my circuit as shown above. The capacitor has zero initial values. Why is the output voltage shifted by 3V? The original purpose of the circuit is to implement a PI controller....
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1 answer
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Transimpedance amplifier resistor calculations

How are the values of resistors in this transimpedance amplifier calculated? Also, why is a resistor divider used in the feedback path?
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How can I best diagnose this solid-state Fender Sidekick Switcher in need of repair? [closed]

I am working on an amplifier that belongs to my dad. The story goes that in probably 1993, when I was 2 years old, I got access to a Phillips screwdriver and took this amp apart while no one was ...
1 vote
2 answers
162 views

Op-amp: finding out how it works

With both feedbacks, why do I use something like "stronger negative feedback" or "stronger positive" feedback? I've read that when I supply a negative potential to the negative ...
-1 votes
3 answers
133 views

How do you calculate Vout/Vin in this circuit? [closed]

I don't quite understand how you are supposed to get the voltage going to the first op-amp. I do understand how I would get the answer from that point forward.
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2 answers
407 views

How to calculate gain (op-amp)? [closed]

This is a microphone pre-amp circuit (from an old project): How do I calculate its gain, especially in dB?
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Discussion on demonstrating saturation in operational amplifiers with positive feedback, and simulation problems

I have been dedicating my time to the study of Operational Amplifiers for the past few weeks. I understood that an amplifier in an open loop configuration has a very high gain, in the case \$A \to \...
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1 answer
57 views

Does an op-amp's input-referred noise increase or decrease with decreasing supply voltage?

I plan to use the OP97F in an application using a single 5V supply, but all of its parameters are listed for +/-15V supply. There's a noise density graph showing it's valid from +/-2V to +/-15V but I'...
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1 vote
1 answer
151 views

Photodiode detector 2-stage amplifier design

I found the post with circuit diagram I wanted to build: circuit diagram. The resistors values, gain and filter frequency are enough for me. I wanted to measure light intensity as DC voltage, so ...
1 vote
1 answer
49 views

Multiplier and divisor using logarithmic and anti-logarithmic op-amps, issue with output

I was tasked to make 4 processes using operational amplifiers: adding, substraction, multiplication, and division. However, only the add and substract operations work: whenever I try to multiplicate ...
2 votes
2 answers
74 views

Op-amp stable voltage gain out of different input value

Can anyone tell me how to make a circuit with unstable input voltage signal value to a stable output value For example: A sinewave in the input between 1 Vrms to 5 Vrms The output must be a stable 10 ...
1 vote
1 answer
80 views

Feasibility of high-speed omnidirectional communication through infrared light

I am currently working on the design of a low-cost communication system based on IR LEDs and photodiodes for my research project. The goal is to transmit data with ~100ns pulses across ~0.5m distance (...
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1 vote
0 answers
79 views

Low intensity UV light detector

I wanted to build low light UV detector, I mean the measurement of light with wavelength 405 nm. I found two schemes: First circuit: And the second circuit: I wanted to use operational amplifier ...
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2 answers
43 views

Linear phase with audio amplifier

I came across the following amplifier for an audio ADC input stage in an application note for the CSxxxx codecs (appnote, figure 2. Codec datasheet. VQ is approximately 2.7V for biasing.): I did an ...
1 vote
1 answer
213 views

Op-amp - audio starts only after a few seconds

I am trying to make a simple audio mixer with several audio jacks as input and one output to headphones. I built a circuit on a perfboard using an LM358A with only a positive power supply. It seems ...
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2 votes
2 answers
90 views

Is there also equal voltage on the inputs of an op-amp with a capacitor in the feedback rather than a resistor?

It can be mathematically proven that when we have a resistor in the negative feedback of an op-amp, the input voltages in the inverting and non-inverting terminals get equal. I'm wondering if we can ...
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Negative feedback divider calculation for NE5532

I have this "Switched Gain" circuit from Douglas Self's book. I want to implement the same topology but with different gain in decibels: 0 dB, 3 dB, 6 dB and 12 dB. I need a method/formula ...
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3 answers
76 views

Op-amp output as gate voltage to MOSFET

As I understand it, the MOSFET here provides negative feedback to the closed-loop op-amp configuration. Hence, Vout2 = 1 V. Thus, the current through NMOS = Id = 1 mA. So Vout1 = 5 - (RD·Id). Then ...
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Sample analog signal with stm32 uC

I need to sample an analog signal from sensor that indicates if the camera is in movement - I need to identify if the camera is scanning or stop scanning from any problem and report it to Stm32 uC. ...
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1 vote
0 answers
74 views

Amplifying electret microphones with wrong bias power

I have an issue. I'm making a device that can switch between two microphones for a two way radio. The microphone that comes with the radio is an electret microphone that gets its plugin/bias power ...
0 votes
1 answer
84 views

How to calculate voltages in op-amp circuits?

I don't know how to solve the following problems; I don't even know what the best way to start solving them is. Can someone help me with the calculation steps so I can then try to solve them on my own?...
3 votes
2 answers
114 views

Is the cut-off frequency of a 4th-order filter at -12 dB or -6 dB?

I designed a 4th-order active Linkwitz-Riley crossover filter by cascading two 2nd-order Linkwitz-Riley filters. Below are the simulation results. The red and purple waveforms are taken at the output ...
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-1 votes
1 answer
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Second-order LPF not filtering correctly

I am trying to implement a 2nd-order Butterworth low-pass filter with a cut-off frequency of 9 kHz. As an input I was using a square wave of 12 kHz. My op-amp rails are 0 and 5 V. The sqaure wave has ...
0 votes
0 answers
77 views

Can I use a resistor to transfer voltage to current rather using transconductance amplifier?

The situation is I intend to transfer voltage to current to control a laser. The voltage comes from an optical phase-locked loop (OPLL). It is changing over time, so the current transferred from this ...
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3 votes
2 answers
106 views

Wrong frequency from a phase shift oscillator

I found the enclosed circuit on the internet. There were plenty more like it so I would have thought it should work. The output is supposed to be a good sine wave at \$\frac{1}{2.6 RC} = \small 38\...
2 votes
2 answers
103 views

Voltage-controlled current source design problem

I am trying to design a voltage-controlled current source circuit. After some research, I decided to use an op-amp. In the circuit shown below, when V1 is 0.3 V, then Vr is 0.3 V and the current is 0....
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1 vote
3 answers
196 views

Do you need a closed-loop op-amp to get an unweighted voltage subtraction?

I will be quoting this article. In a closed loop op-amp circuit the output pin of the op-amp is connected with the either of the input pin to provide a feedback. This feedback is called as the closed ...
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-2 votes
2 answers
59 views

Sawtooth Current-Limiter

I have a sawtooth waveform passing through two resistors shown in the configuration below. R200's value is unknown until it gets measured. I need to adjust the value of R100 to set the peak current ...
1 vote
1 answer
70 views

Op-amp amplifier for Hall sensor: grounding

I built a simple LM741 non-inverting amplifier with a fixed gain of 3.1x and verified it works for a simple +0.3 VDC input on pin 3. It uses a dual power supply consisting of two 9V batteries in ...
4 votes
3 answers
127 views

Find RC values of a second-order low-pass filter

I have a low-pass filter of second order. The transfer function is: $$\small G(s) = \frac{1}{R^2C^2s^2+(3CR - CR)s + 1}$$ And the amplitude function is: $$\small A(s) = \frac{1}{\sqrt{(R^2C^2s^2)^2 + ...
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3 votes
3 answers
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Op-amp - minimal differential voltage?

I want to implement a PT100 sensor measuring circuit using a Wheatstone bridge. Below is a link to the implementation that I suggested. https://www.instructables.com/Measuring-Temperature-Using-a-...
9 votes
5 answers
2k views

Why are there two power sources for some amplifiers?

In this diagram the DC power sources for a linear amplifier are shown: We see there are two separate batteries connected to it, and then to ground on opposite ends. Why must there be two separate ...

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