Electrical Engineering Stack Exchange
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Questions tagged [feedback]

Feedback is a process whereby information from an output of a signal is used (intentionally or unintentionally) to alter the input of the same signal. Commonly used in operational amplifiers. An everyday example is the high-pitched audio frequency heard when a microphone picks up audio from its own amplified output.

There are two basic types of feedback: Negative and positive.

Negative Feedback: When the output is used to attenuate or diminish the input signal. Commonly used to correct errors or limit levels to an acceptable value. Negative feedback occurs when the output is between 90 and 270 degrees out of phase with respect to the input signal.

Positive Feedback: When the output is used to amplify or enhance the input signal. Can be used to decrease sensitivity to small signals or noise. Positive feedback occurs when the signal is in phase with the input signal.

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How negative feedback increases the bandwidth

Negative voltage feedback affect all the frequencies equally. Hence by simple observation it is clear that, negative feedback doesn't affect the bandwidth of the circuit. But in many books, it is written that negative voltage feedback increases the…
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Having hard time to identify feedback types

update: I have read similar questions on ee.se, they helped a bit, but it is still hard to understand the type for example in the question in figure. Maybe, you can just explain specially the question below. Series-shunt, shunt-shunt, current…
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What is the feedback \$\beta\$ for this resistor feedback?

The first is the schematics from NMOS4 with parasitic capacitance: What is the feedback \$\beta\$ for this resistor feedback? And Should we include the capacitor \$C_{gd}\$ for this feedback? The following is the asc file for whom is…
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Closed-loop pole moving to RHP - less stable or more stable?

I was reading Razavi's Design of Analog CMOS ICs book and came across this in the Stability and Freq. Compensation chapter, What the book says The closed-loop transfer function of a system is given by the following: It then goes on to say…
AlfroJang80
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How does not using common-mode feedback drive my outputs to the rails?

Consider the following circuit in Fig 9.31 (a) Now, essentially, summarising the block of text, it seems that due to some mismatch between PMOS and NMOS devices or fluctuations in bias voltages, the current that Iss/2 pulls may not equal what the…
AlfroJang80
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How can one distinguish between negative feedback types?

There are several negative feedback types, like voltage shunt, voltage series, current shunt, andcurrent series. I can distinguish between them with op-amp or box diagrams very well (it's easy I guess), but when it comes to the point when we use…
Aykut Dos
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How can we identify feedback network in this circuit?

The following is a figure from 8.47 in Design of Analog CMOS Integrated Circuit, page 301: The book tends to suggests that feedback network However, I have a different opinion.
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Open the loop in voltage-current feedback

The following is a figure from 8.61 in Design of Analog CMOS Integrated Circuit, page 311: Here is the question: Calculate feedback \$\beta\$ of the following circuit: As we use the method of the book, we have to ground both of two terminal…
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How to find feedback coefficient \$\beta\$ of this current-voltage feedback circuit?

Here is the circuit from YouTube: In order to determine the feedback, we have to break the loop at the gate of M1. Assume A is \$\infty\$, so \$V_{GS}\$ of M1 is 0. As we know the \$V_S\$ of M1 is grounded, we have \$V_S = V_G = 0\$. And that's why…
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why is my analysis for this resistor \$R_F\$ feedback network different from the book answer?

The following is from the book Design of Analog CMOS Integrated Circuit, page 313. Calculate the voltage gain of the circuit. (channel length modulation and bulk effect are neglected) At Node X with the help of KCL. $$\frac{V_{in} - V_x} {R_S} =…
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Is feedback positive or negative for this closed-loop circuit?

The following is from the book Design of Analog CMOS Integrated Circuit, Page 307. I think feedback is negative in my opinion. Here is what I think, see picture below.
kile
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Expanding BW using feedback

I have built the following two stage amplifier as shown below. In open loop I get 63 dB gain and BW about 3 kHz. When I tried to add a feedback resistor to lower the gain and increase the bandwidth as shown in the formula below I get no change at…
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How to find Topologies of an amplifier?

How can we find the topology of an amplifier's feedback? I was asked to find the feedback topology of the following circuit, The following observation is made by me: Since the o/p voltage is connected with the feedback directly i.e R1, it will…
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Negative Feedback Factor

As of now most of the negative feedback systems I have encountered have a feedback factor that is less than 1 but positive. However in some situations it seems the system can behave as positive feedback if the feedback factor is not negative.. I…
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speed control loop percent error

I'm having trouble understanding the percent error from the following closed loop feedback equations. \$w =1\$ is the road grade change and \$r=65\$ is the speed control input, and given closed loop output speed \$Y_{cl}\$ and closed loop error…
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