Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers,

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105 views

Why does an OpAmp with negative Feedback not amplify the potential difference on his inputs?

An OpAmp without any feedback just takes the potential difference between his 2 inputs and amplifies it by a certain factor. I know that in an OpAmp Circuit with negative feedback, we can make the ...
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2answers
44 views

which amplifier must be used for measuring the current?

one question. I saw to measure the current in SMPS sometimes we use the shunt resistors and then use op amp or differential amplifier orcurrent sense amplifier or instrumental amplifier or ...
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1answer
75 views

Opamp circuit stability (LTSpice)

I want to study the stability of my opamp circuit with LTSpice, I found this video as tutorial: tutorial on phase margin So, I did the simulation with closed and open loop as suggested and got the ...
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2answers
69 views

Splitting plane for negative power supply

I used op-amp for my project and supplied with +12 and -12 volts. My PCB will have 4 layers which are TOP (signal layer), POWER (internal plane), GROUND (internal plane), BOTTOM (signal layer). When I ...
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0answers
34 views

Choice of passive components for AD549/AD630 low-noise circuit?

I'm trying to reproduce an "ultra" low-noise amplifier circuit which calls for several precision amplifiers/modulators (AD549/LF356/AD630). The input source is a Hamamatsu S1223 photodiode capturing a ...
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2answers
59 views

Understanding Noise Generator Circuit

I am looking at Figure 13.119 in The Art of Electronics, which shows a psuedo random bit sequence generator using shift registers. I understand how this functions. It then takes taps off of the shift ...
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2answers
74 views

Eliminating oscillation in a feedback circuit

I have built a switch-mode power supply where the output voltage is controlled by a PWM signal from a microprocessor. The power supply is based on an XL4015. The feedback pin is normally fed by a ...
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0answers
56 views

Range of resistance for which the Operational Amplifier is saturated

In the image above I have a variable Rf, and I am asked to find the range for witch the Operational Amplifier is saturated. This is what I know: R0=R3 = 1.5K ohms R2=5R0 RL=4R0 Vi=30V The operational ...
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1answer
76 views

LM358P Op Amp Output Stays High

I want to PWM lights with Arduino and IRF3205 N-channel MOSFET. For fully turning the MOSFET on I am using this circuit. The op amp (datasheet here) and load are powered by a single 12V source (lead ...
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1answer
79 views

What do you call unity gain? 1V/V or 1V/V plus a small tolerance?

I designed a two stage single ended op amp with an internal frequency compensation. There's a minor problem that I noticed in my loop gain transfer function. I forced the gain to reduce to around 0....
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1answer
103 views

Purpose of this capacitor?

What is the purpose of the C2 capacitor in the feedback loop? What is the time-constant of the R4/R5/R6/C2 net? This is for a pH-probe. Source
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1answer
45 views

Simple Issue With Ground on Circuit Connected to Raspberry Pi Zero

This circuit is my attempt to reiterate a circuit I already have working two times over. The circuit is an infrared detector, using a photodiode and two op amps to get the voltage and current to the ...
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3answers
1k views

Understanding this peak detector circuit

I think the circuit attached below is a peak detector because of the diode, resistor and capacitor at the op-amp's output. What I don't understand is the diodes on the input side. The input signal ...
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2answers
85 views

Non inverting op-amp resistors

I came across this schematic It's a non inverting op-amp configuration with an audio input. And i was wondering what the POT and R3 do? I assumed the pot to set a bias voltage but then what does ...
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2answers
40 views

Active band pass filter + offset

I'm trying to know the fr equation for the following op amp configuration: I have some capacitors values for specific fr frequencies: fr = 34Hz -> C = 33nF fr = 50Hz -> C = 22nF fr = 160Hz -> C = ...
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3answers
652 views

Not understanding how the gain works in the 1st stage of an instrumentation amplifier

For the following instrumentation amplifier, I am having some confusion understanding the gain process for the 1st stage. I understand that the 2 input amps are essentially 2 non-inverting amplifiers ...
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2answers
145 views

Criticism of my differential pH probe design

I finished and tested with buffers this little differential pH probe on a perfboard, it works, 3 points calibration is linear. The ground electrode is a stainless steel rod wired to the GND of the ...
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0answers
33 views

Differential input pH schematic reading

I am trying to understand the following schematic for a differential input pH probe. here is the link A1 and A2 role are unity gain opamp amplifying high impedance probe signal, while A3 makes the ...
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1answer
56 views

Why is a Instrumentation Amplifier Necessary for A Wheatstone Bridge (small signal circuits)

I do not understand why an Instrumentation Amplifier is Necessary for small differential signals? Why is it necessary that the initial inputs to the amplifier must be high impedance from the ...
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1answer
74 views

Why is an Instrumentation Amplifier Used Over a Standard Differential Amplifier? [duplicate]

I am having a bit of a hard time understanding why instrumentation amps are used over a single differential amp? For example, the differential signal that I have is very small and comes from a ...
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1answer
164 views

Are there well known simple operationnal amplifier circuits designs to make purely analog squaring amplifier (for experimental analog computing)?

In order to make analog calculation (for analog regulator simulation), what would be the means to make an squaring amplifier ? There is an obvious solution with a multiplier circuit as pointed here; ...
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2answers
64 views

instrumentation amplifier with [2 opamp + ADC] vs [3 opamp + ADC]

I have an 16bit ADC able to do differential measurement with range -5V to +5V (ADS1115), do you think both circuits would work? It's required that the adc input is within -5V and +5V range, else it ...
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1answer
90 views

Deriving The transfer Function of a high Pass active second Order filter

I have recently been trying to solve this transfer function an my professor keeps saying I have been doing wrong and I finally need help. I know my Gain is \$1+ \frac{R_A}{R_B}\$. but I keep getting ...
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2answers
29 views

How to calculate an op-amp's current usage based on datasheet's supply current and its Vout terminal?

This might be a dumb question so if yes, I apologize. I would like to power an op-amp off of a boost converter and I need to know how much current an op-amp would use. I'm using TI's web bench and ...
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2answers
56 views

Basic OpAmp as a Comparator question

I'm continuing my refresher on electronics, and want to validate a conclusion/deduction that I'm reaching. Consider the two comparator circuits below: In both cases: I have chosen not to picture ...
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1answer
33 views

Digital signal into the video cable

The input signal is simply composite sync signal, without any additional video information. It is CMOS - 0 to 5V levels. I need the same type of signal to appear in the cable along with the RGB lines. ...
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1answer
69 views

Node voltages in the first-order op-amp circuit

Here is a first-order op-amp circuit: I have to find V0 given that V(0) = 4 V (i.e. the capacitor is charged). If the capacitor is charged, then the voltage at the node 1 is V1 = 4V and KCL must look ...
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2answers
79 views

Simple Op Amp Non-inverting Amplifier Circuit Not Working

I am only just starting to learn about circuits and electricity, so please bare with me. I am attempting to build the circuit pictured below: And this is my rendition of it: Here are the parts used:...
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0answers
75 views

op-amp voltage follower - input volt is not equal to output volt

This is a fundamental question but I may be stuck in somewhere. I have a circuit as below, the red texts are the actually values by a multimeter. As you can see, for op-amp1 output, the simulator is ...
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0answers
44 views

Can I use Highspeed Opamp as differential clock driver?

I want to use high speed Opamp LT1364 as +/- 15V clock driver of same voltage instead of typical CMOS / CCD clock drivers with lower voltage and slew rate. CMRR : 90dB PSRR : 100dB Slew rate : 1kV/uS ...
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2answers
92 views

Op-amp circuit to control gain of two analog channels with one single-section potentiometer

I'm working on designing my own headphone amplifier with extremely high fidelity. One thing I want to incorporate is a circuit to control the gains of the two channel's using one single-channel ...
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3answers
92 views

I set up an amplifier (LF351) for a gain of 5.7, but it is saturating. Do I have to utilize the offset null pins?

simulate this circuit – Schematic created using CircuitLab The feedback network I am using is a voltage divider with 4.7K and a 1K resistor. The node after the 4.7K resistor is connected to the ...
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2answers
165 views

Which is the preferred approach to PCB layout for signal vs power traces in analog circuits, and things to consider?

I have had to layout 2 layer PCBs several times now for analog signals, and am just beginning to learn the process. I often face a similar question in one form or another with regard to laying out ...
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0answers
45 views

About the differential gain [duplicate]

Let's consider any circuit which contains a differential pair, for example a telescopic cascode single stage OTA: In every circuit like this one, my professor and every book compute the small signal ...
3
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1answer
110 views

Using op-amps to read real-time resistance values over a wide range

Background I have been using a simple inverting op-amp circuit and Arduino to measure the resistance of a photoresistor (light 5k, dark 200M), like in the schematic below. This provides linear data ...
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2answers
95 views

Question about differential signals and feedback

Let's consider, for example, this circuit: During lessons, our professor always assumed perfect differential input (two signals with the same dc value and with equal and opposite amplitudes). As a ...
2
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1answer
55 views

Clamp a D/A to prevent output below 0V

I am using a USB D/A converter to drive a high-voltage op-amp with a signal between 0 and 3V at 10 kHz. The D/A I am using is capable of outputting between -10 and +10 and unfortunately seems to ...
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0answers
53 views

Opamp output on loaded and unloaded cases

I have a design project to rotate a motor. In order to do that, I have designed a very simple but smart circuit. However, in signal comparison stage, if it is unloaded, i.e. not connected with the ...
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3answers
67 views

INA168 vs INA169 High-side current sensing

I have read the datasheets of the INA168 and the INA169 and can't see any difference, other than internal resistors value and quiscent current (25uA for INA168, 60uA for INA169). Those two were even ...
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1answer
57 views

Instrumentation Amplifier Connection Problem

I am trying to build a circuit capable of measuring ECG signals following the scheme attached. Since AD623 was out of stock, i ended up buying something like this: https://www.arduino-tech.com/cjmcu-...
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1answer
67 views

Best way to connect balanced audio line to ADC (with volume pot)?

Sorry for this more longish question: I'm currently collecting some ideas for my next project where I want to connect an external balanced audio line level signal to an ADC with differential inputs (...
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0answers
49 views

pH sensor voltage versus pH

I am currently in the process of making an ultra-low power pH captor and I'm running in a problem. The voltage I get from my pH probe does not fallow the Nernst equation (which states that the voltage ...
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2answers
40 views

Switching multiple photodiode inputs to an op amp

I am playing around with LEDs as (semi)wavelength selective photodetectors and have reproduced the circuit found in Forest Mims' Make article: I have an operational circuit using an LM358 powered by ...
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3answers
105 views

Microvolt to milivolt/volt amplifier with common components

Suppose one has access to common components and gear only : basic milivolt multimeter, badly regulated supply, linear regulators, 1% resistors, common BJT/FET, voltage references like LM431 or zener ...
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2answers
36 views

Working of INA826 instrumentation amplifier for Pt100 RTD

The schematic below contains an INA826 used to amplify the resistance of the Pt100 RTD across J1. Gain is set to 10 through the 5.49K ohm resistor. Is this ciruit amplifying only the voltage across ...
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1answer
63 views

Photodiode to an ADC

Please bear with me as I'm not too experienced with this. I'm attempting to use an ADC to get readings from a photodiode. From what I understand, I should likely use an op-amp as the range of the ...
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4answers
181 views

Question about differential signals as input of an operational amplifier

I'm studying the circuits which are used to implement operational amplifiers. For example, I've studied the two stages amplifier (in which the first stage is a differential amplifier with differential ...
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2answers
51 views

Split output of one temperature sensor to two independent signals using an op amp buffer [duplicate]

First off I am a car guy, if I have a schematic or details I can solder what I need. I have a client that fitted a digital temperature gauge to his car, he also wants to have the gauge on the ...
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0answers
51 views

Chua's circuit's pattern not fully shown

I have made a Chua's circuit, and hooked a soundcard oscilloscope to it, to measure the voltage across C1 and C2. Circuit diagram: Source:Kennedy 92(pdf). Software used: soundcard scope. The ...
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1answer
73 views

Grounding an audio signal

I'm building a simple audio mixer. It's going to be running from a USB power supply, so I'm using a TLE-2426 to derive a 2.5V reference voltage for the summing op-amp. My question is, what do I ...