30 votes
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How to identify filter behaviour without memorizing different topologies

Look at the extremes. DC and very high frequencies. For DC you can remove the capacitors and short the inductors. For high frequencies you can short the capacitors and remove the inductors. By looking ...
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  • 7,955
12 votes

How to calculate values for decoupling capacitors

Basically you want something close enough to the pin that at the edge rates in play the bounce is not too bad, and then something further away with (possibly) enough ESR to damp everything to keep the ...
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11 votes
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Why is the output of a high-pass filter not 0 when the input is 0?

This could arise as the sum of the input offset voltages ... but for 3 opamps, that would only come to 3.9mV worst case, so that isn't it, especially since it's unlikely that the SPICE model has the ...
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10 votes
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Design constraints when dealing with very high resistances in op amp's feedback loop

I used to do condenser microphone stuff professionally, which was very much this kind of thing (10G ohms with maybe a 30pF source). Cleanliness is VITAL, a bit of skin oil in the wrong place and you ...
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9 votes
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What is the purpose of the 250uF capacitor in the LM386 circuit?

Yes, 470uF will work fine, it will just extend the bass response somewhat. It's a coupling capacitor (or a blocking capacitor, to block DC, if you prefer). The 10R + 50nF is a "Zobel Network", ...
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9 votes

Conundrum: High pass filter passes DC?

The resolution to the conundrum is that there really is no conundrum. Your input, a step function, has infinite dc component (its Laplace Transform, \$1/s\$, goes to infinity as \$s\rightarrow 0\$). ...
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9 votes

Conundrum: High pass filter passes DC?

You're confusing the steady-state response with the total response. The transfer function for that circuit is: $$H(s)=\frac{s}{s+\frac{1}{RC}}$$ and if you solve for the step response: $$h(t)=\text{e}^...
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Will capacitor in high pass filter pass high frequencies while it is blocking low frequencies?

And at low frequencies and DC currents the cappacitor gets fully charged very early at the beginning of the cycle and acting afterward as an open circuit until the voltage drops in the second half ...
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7 votes

How to calculate values for decoupling capacitors

tl; dr: it’s not just about the cap values, but their parasitics too. The data-driven technical answer is, you model it if you have access to the very expensive power integrity software that takes ...
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7 votes

Why is the instrumentation amp distorting the signal on the input?

I believe the problem lies in the placement of just one wire in your schematic. Try this: I've kept the RC time constant the same, but chose somewhat differently for the resistor and capacitor values....
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7 votes

Why is the instrumentation amp distorting the signal on the input?

The bumps come from the current flowing into the output capacitor with those "real" 0.65 ohm resistances, and since you have coupled the inputs through the (-) power supply rather than ...
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6 votes
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What is the purpose of the series of actions: amplification, band-pass, rectification, and low-pass?

The signals from the sensors were tiny, and needed to be amplified. Otherwise they would be lost in the noise in the rest of the system. When "interesting" things happen, neurons fire rapidly. ...
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6 votes

High Pass vs Low Pass simple Circuit (RC vs CR)

For years I tutored the very first electrical engineering course at my uni, so this comes up a lot - don't worry :) The best way to understand this is to think about all 4 cases: An AC (or, you ...
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6 votes

RC differentiator giving a higher output amplitude than input amplitude

It's called "charge pumping", and it is sometimes used to create low-power boosted-voltage supplies for some applications. At the end of each half-cycle, the capacitor is essentially charged to the ...
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6 votes
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RC differentiator giving a higher output amplitude than input amplitude

Think of a capacitor as "liking to keep the voltage across it constant" - at least in the short term. Figure 1. Voltage difference analysis. Just prior to the squarewave step down at (1) we can see ...
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5 votes
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Will a resistor connected in parallel with a high-pass filter affect the filter cut-off freq?

The "trick" you lack may be using the superposition principle to "ignore" (temporarily) the DC source and consider it to be 0 V while studying only the AC source. Using the superposition principle, ...
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Biasing an AC voltage for input to ADC

The ADC input floats to some DC voltage. If you disconnect your voltage divider from the ADC, you will see the voltage on the ADC float to some DC voltage. The ADC input looks something like this: ...
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5 votes

What is the purpose of the 250uF capacitor in the LM386 circuit?

Figure 1. Typical LM386 amplifier circuit. For an audio application driving a loudspeaker alternating voltages must be generated. A positive voltage on the output drives the speaker cone one ...
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5 votes
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How to design a 2nd Order High Pass Butterworth filter with a gain of 6 dB?

First I don't understand why you are refering to page 450 of the book; I found your circuit on page 456. Figure 11.23 "High-pass equal-component" (VCVS). In the book they describe two types of ...
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5 votes
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Questions about the baxandall circuit

Your circuit is indeed a tone control circuit. For low signal frequency (Bass booster) we can ignore \$C_2\$ and \$C_1\$ because for low-frequency capacitance reactance \$X_C\$ is high. So we have ...
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5 votes
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High pass filter - Cut-off frequency calculation doesn't match simulation

From the simulation, it looks like it fc=500Hz or somewhere around there. Your simulation looks more like 15 kHz (3 dB point) and the reason is because you haven't used enough resolution in your AC ...
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High pass filter - Cut-off frequency calculation doesn't match simulation

Well, mathematically speaking we can write: $$\mathcal{H}\left(\text{s}\right)=\frac{\text{sL}}{\text{sL}+\text{R}}\tag1$$ Using \$\text{s}=\text{j}\omega\$, we get: $$\left|\underline{\mathcal{H}}\...
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5 votes

Conundrum: High pass filter passes DC?

The circuit you are describing and the output is shown below. Let me know if I got it correct. There is no conundrum here. The HPF (capacitor) allows high frequencies to pass. The step voltage has a ...
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5 votes

How can I find the cutoff-frequency in real experiment?

It seems to be your task to figure out how to do this, and we don't solve homework for people. But your actual question here seems to be: I don't understand why I should find the method to determine ...
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5 votes

I need to design a second-order high-pass filter, gain 2 and cut frequency of 500 Hz. Using chebyshev response of 0.1 dB

Here's your diagram with some annotations: Although I've never seen this particular arrangement before, I'll argue that the above can be reduced to: Where \$R_2=\frac{R_a\,R_b}{R_a+R_b}\$ and \$A=\...
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4 votes

Is this phase shift oscillator design correct?

Both of the other answers are correct, but you might find the numbers instructive. Let's start at the output of the right-hand capacitor. It feeds a very high-impedance load, and the phase shift ...
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4 votes
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Is this phase shift oscillator design correct?

No - it is not the classical phase-shift oscillator. The resistor from the inv. input to ground makes no sense. It must be replaced by a series resistor (in series with the last C) in order to allow a ...
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4 votes
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Step Response of 2nd Order HPF

The double zero at \$ s\small =0\$ gives rise to the undershoot. To make the analysis easier, it's best to normalise the TF to \$\omega_n=1\$, thus divide \$\omega_n\$ by \$\small 1000\$ to give: $$G(...
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4 votes

How do High and Low Pass Filters function

A low pass filter on the left, a high pass filter on the right simulate this circuit – Schematic created using CircuitLab Each has a -3dB, or corner, frequency of around 1600Hz. This will fall ...
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