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

Without knowing how your actual circuit is built, it is going to be nearly impossible to help you to track down the origin of the noise you are observing. Is it wired up on a breadboard? Are you using ...
2 votes

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

Your circuit is missing decoupling capacitors on all integrated circuits. You have unconnected op-amps in your OP-490. The unconnected op-amps can pick up noise from the environment. They may also ...
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1 vote
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Why make second stage current larger than input stage current in op-amp?

The maximum current available for charging and discharging Cc is either the first stage current or the second stage current, whichever is smallest of the two. So the slew-rate roughly depends on the ...
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1 vote
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Why is one op-amp in my circuit messing up the other?

Intuitively, R1 and R5 both pass the same current, and by Ohm's law that means R1 drops over \$\frac{2}{3}\$ of the signal. The same goes for R2 and R6, and this is why the signals appearing at ...
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1 vote
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Current flow in non-inverting op-amp amplifier

There are a couple of points that make things much easier: Current doesn't flow into or out of the op-amps inputs, because they have infinite impedance. It's as if the op-amp isn't even there. With ...
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0 votes

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

When you insert the 3rd op-amp (diff) the first series resistors (R1, R2) become part of the 3rd op-amp's active circuit. Remove the first set of series resistors. If you really want the extra 10K of ...
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3 votes
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Finding poles by inspection - 2 resistors

Is this correct? Yes, that is correct; R2 feeds a virtual ground hence it acts like a resistor to 0 volts. Then, if you Thevenise R1 and R2 to find the effective resistance of the source (Vin) you ...
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3 votes

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

Calculate the magnitude of \$T(s = j\omega)\$ when it is not acting as a filter (which is as \$\omega \to \infty\$ for a high pass filter). $$|T(j\omega)| = \left|-\frac{R_2}{R_1}\right| \times \frac{|...
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2 votes

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

How can I get 3 dB frequency from transfer function? It's simpler than that; the half power point (commonly know as the -3 dB point) is when: - $$R_1 = X_{C}$$. And we know that \$X_{C} = \dfrac{1}{\...
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1 vote

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

From the transfer function DC gain is 1 so
0 votes

Current flow in non-inverting op-amp amplifier

How does the current flow in this particular circuit? What is an ideal op-amp? See this first. LF13741 is a FET input op-amp. Note that R3 current is very low and should be zero. And here is same ...
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3 votes

Current flow in non-inverting op-amp amplifier

Assuming it's an ideal op-amp so no current flows into the op-amp terminals and V+ = V- = Ve. So, current flowing through R3 is 0. Current through R4 is Ve/R4. Apply voltage divider to get node ...
2 votes
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Biasing a low AC voltage for input to an ADS1115 ADC

The 16-bit w/PGA ADC ADS1115 is not ideal here because the internal reference voltage is inaccessible. Input voltage must be kept in the range between the power supply rails at all times. You could do ...
0 votes

Biasing a low AC voltage for input to an ADS1115 ADC

As I can see, the sensor has dual power supplies. NB: I have seen some ADS1115 boards with 2.5V reference onboard. Sorry, mistaken. It is AD7705, AD7705 16-bit ADC Data Acquisition. Let's use a ...
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0 votes

Biasing a low AC voltage for input to an ADS1115 ADC

Just use a voltage divider from the sensor output to Vdd, and it will shift the signal to 1/2 Vdd, although half the amplitude. simulate this circuit – Schematic created using CircuitLab
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2 votes

Can noise back-feed through an op-amp?

If you have EMI on the output, you have to first ask how is it getting in there? Two main possibilities come to mind: the output trace is long and next to a source that is emitting a lot of ...
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2 votes

Can noise back-feed through an op-amp?

Yes, it could, however it would likely be small. The output resistance of the op-amp at reasonable frequencies is something like 100 ohms in that configuration and there is some small coupling between ...
-1 votes

Can noise back-feed through an op-amp?

Short answer, No. It cannot travel through the op-amp without damaging it. The noise will travel around the op-amp through the feedback components wire. So yes the noise will appear on the non-...
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0 votes

Op-amp comparator circuit design for high/low voltage measurement

What you need is a window comparator, which is basically what your schematic is. However, yours is a modified version of the one blow. Information on these is readily available on the Web. For your ...
2 votes

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

Your method will estimate the power delivered by the op-amp to its load, but it won't estimate the power consumed by the op-amp itself. To estimate the power consumed by the op-amp, you can treat it ...
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2 votes

Photodiode detector 2-stage amplifier design

This is a difficult problem, so you want to do everything possible to maximize the sensitivity. I a building something similar to what you need. Opamps usually work better with dual supplies, a single ...
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2 votes
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Input noise of ADC AD7768 with opamp driver ADA4945-1

With the inputs floating the gain is not unity. There is an infinite resistance between the \$470 \Omega\$ resistor and ground. The op-amp gain in the floating case is: $$\underset{R_{i}\rightarrow\...
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0 votes

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

Neglecting the problem about whether the time constant of 100 ms can be achieved with what you have shown and what you propose to add to the circuit (hint, the integrator you have drawn will simply ...
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How do you calculate Vout/Vin in this circuit?

I don't quite understand how you are supposed to get the voltage going to the first op-amp. The voltage ( I will call \$V_{a}\$) at the non-inverting input of the first operational amplifier is the ...
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4 votes

Op-amp: finding out how it works

Using NFB and PFB It's really nice that you are writing so much in response to others. You are trying at something. I'm not sure what it is, but I'm going to pick up a few of your bread-crumbs and ...
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Transimpedance amplifier resistor calculations

First of all, a transimpedance amplifier is a current-to-voltage converter. So you should replace V2 with a current source in your simulation. Well, I think C1 should be connected across R1 (i.e. R1 ...
3 votes
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Op-amp with capacitor showing output voltage of 2.98 V despite 0 input voltage

Your amplifier has a capacitor in the negative feedback loop so it will behave as an integrator. Any input bias current will be integrated causing the output to ramp up or down, depending on the ...
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4 votes

Op-amp: finding out how it works

why do I use something like "stronger negative feedback" or "stronger positive" feedback? I don't know why you "use" something like that. It sounds like nonsense, and is ...
4 votes
Accepted

How do you calculate Vout/Vin in this circuit?

The op-amps are configured as voltage followers. Assuming that they're ideal, we have an equivalent circuit as follows: simulate this circuit – Schematic created using CircuitLab The voltages ...
0 votes

How do you calculate Vout/Vin in this circuit?

In your place, I would proceed in 3 steps : Assume the voltage for the + input of the first op-amp is a "known" function V1+(t), and use this to compute Vout(t) (it will depend on V1+(t)) ...
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4 votes

How to calculate gain (op-amp)?

In addition, C34 acts as a higher resistance at low freqencies (below 1/(2.pi.R.C) = 1/(2 * 3.14 * 680 * 100n) = 2.3 kHz. Thus gain rolls off towards 1 at frequencies below 2 kHz (the 100 nF likely ...
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6 votes

How to calculate gain (op-amp)?

You compute the gain of that circuit by scraping away bits of it until it looks like a basic OP-amp circuit; then you look at the textbook gain for that circuit. R27 and R29 are there to provide a ...
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7 votes
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Does an op-amp's input-referred noise increase or decrease with decreasing supply voltage?

Noise in most circuits depends on bias current in the critical components. It is easy to make bias currents quite independent of supply voltage with an internal current regulator. There is no reason ...
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0 votes

Phase noise of op-amp

Op-amps don't really work well in frequencies above 1 MHz with some exceptions of high precision Op-amps. Are you sure your design is correct? If you do a Bode plot of the gain of the op-amp with the ...
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2 votes
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Op-amp stable voltage gain out of different input value

What you're looking for is an Automatic Gain Control (AGC) system. And it is not so simple to design one with such little information. I'd not suggest any implementation with such little details. You ...
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0 votes

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

Note that your inputs are a bit "too high" (should work, but ...). Log amplifier can work better if you add "offset" correction as in this circuit (NB op-amp are J-Fet input ...
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1 vote
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Op-amp output as gate voltage to MOSFET

For the MOSFET, \$V_{DS} = V_{out1} - V_{out2}\$ and \$V_{GS} = V_{gate} - V_{out2}\$. At the starting, due to closed-loop control for gate, \$V_{out2}\$ is fixed at 1V or the current through the ...
0 votes

Feasibility of high-speed omnidirectional communication through infrared light

I don't see any reason you cannot do this. Light-based communications are unpopular because light is highly directional the components are more expensive than RF, but your requirements are fairly ...
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2 votes

Op-amp stable voltage gain out of different input value

Sounds like you want an AGC (automatic gain control). There are many possible circuits. One approach (simple, but relatively expensive, and only applicable over some range of frequencies) would be to ...
0 votes

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

With an ordinary 2 resistor feedback amplifier configuration, as frequency is increased, the difference voltage between the op amp's inputs increases. This happens because, as frequency increases, the ...
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1 vote
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Linear phase with audio amplifier

On one hand, I learned that linear phase is important to minimize distortions due to the different group delay Yes, important for applications where signal-shape needs to be maintained such as high-...
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0 votes

Linear phase with audio amplifier

The filter presented in the datasheet is should be good enough. The ADC is sampled at 6.144 MHz so you only need to filter extremely high frequencies away, like the datasheet says. The filter is there ...
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4 votes
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Negative feedback divider calculation for NE5532

The math is going to be a bit complicated. The top part of the divider will be in parallel with the 10k resistor R50, so the formula for the gain of this circuit is: $$Gain = 1 + \frac{R_{top}||10k}{...
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7 votes
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Op-amp - audio starts only after a few seconds

Try adding a 100nF capacitor in series with the input. There may be a large value capacitor in the source that has to charge in order to allow your op-amp to reach bias, since your amplifier is DC-...
3 votes

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

First of all, in your diagram, the current through and voltage across the feedback capacitor are in correct. See my diagram. simulate this circuit – Schematic created using CircuitLab The ...
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0 votes

Negative feedback divider calculation for NE5532

Step 1: Convert the desired dB values to voltage ratios. For example, voltage gain of 6dB is a ratio of 2:1. Step 2: Calculate the values for each desired gain value. Ignore the switch for now - you ...
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3 votes
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Differential pair with active load including resistance

Your question about why the tail node is a small signal ground is equally valid for the simple amplifier with a current mirror load. Because that circuit is also not fully symmetrical to be split into ...
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2 votes

Op-amp output as gate voltage to MOSFET

The MOSFET is always in the triode region. The constant current is not a result of the MOSFET being in the saturation region, but a result of the closed-loop system controlling the MOSFET gate. When ...
1 vote

Op-amp output as gate voltage to MOSFET

To meet the "demand" under more strenuous operating conditions, the MOSFET gate has to be driven with a progressively higher voltage. In other words, the change from MOSFET saturation region ...
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2 votes

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

Cascading filters will never preserve the type of response, if the filters are designed so that they are distinct. E.g. if you cascade two Butterworth filters then the result will no longer be a ...

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