# Questions tagged [small-signal]

A circuit analysis method in which non-linear elements are replaced with linear elements whose parameters are determined by a linear approximation of the non-linear element's characteristic curve near its bias point. The result is an equivalent circuit that is a good approximation of the original circuit for signals small enough that the non-linear elements behave linearly (hence the name "small signal").

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### Series capacitor buck converter small signal model

Does anyone know how to do the small signal model of the series capacitor buck converter? I can't find a related paper talking about this one. I think the small signal model is not the same as the ...
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### Is there a typo in this question because I don't think the emitter node of Q2 should be grounded?

In this problem, it's asking us to draw the small signal equivalent of an amplifier but I think the answer they gave is wrong. In the second picture (b) I don't think the emitter of Q2 should be ...
• 35
1 vote
86 views

### Small-signal of CS stage with source degeneration

Can someone explain how Fig 3.30 (c) was created? In particular, the $\large\frac{1}{g_m + g_{mb}}$ resistor to GND. I know you see $\large\frac{1}{g_m + g_{mb}}$ when looking into the source, but ...
81 views

### Wilson BJT current mirror output impedance

I am trying to have a small signal analysis of a Wilson BJT current mirror to find out what is the output impedance. Already I know that the answer is $$R_o=\beta r_o/2$$ In the first step, I need to ...
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1 vote
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### Is the "$\small o$" in $r_o$ short for output or number 0?

You usually see ro in the small-signal models of BJTs or MOSFETs like this. I'm curious if the "o" there is short for "output" or just the number zero? I think I saw people reading ...
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### Derivation help: gain of 2 NMOS in series

I am trying to find the gain (Vout/Vin) of the circuit below, this is not a real circuit that I have, I am just trying to learn more about circuit analysis. The circuit reminds me of a cascode circuit ...
• 509
32 views

### Dupicate LFO Signal and Invert, keeping MAXs and MINs

Im working on a Dual LFO with "Depth" and Rate controls. I already got the "root" LFO signal working and if I do this, I can generate the LFO swinging from 0v to 9v... and with ...
1 vote
66 views

### What is wrong with this MOSFET differential pair analysis?

I am confused regarding the analysis of the circuit on the left and its small-signal equivalent circuit on the right: simulate this circuit – Schematic created using CircuitLab Here is my ...
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### How does a BJT differential amplifier amplify?

I am reading The Art of Electronics. I found a related question here. I understand that differential gain of the amplifier is $$G_{\text{diff}}=\frac{R_c}{2(r'+R_e)}$$ but how? OK, using hybrid-pi ...
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101 views

### Flyback converter small-signal model

I am currently designing a flyback converter and I am interested in measuring the stability of the converter (with a Bode plot). I will try to connect an isolation transformer on the feedback loop ...
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### Determining the output impedance of a part of a circuit with negative feedback

I designed an active discrete baxandall volume control for my project. simulate this circuit – Schematic created using CircuitLab R*(a-1) and R*(a) are supposed to be a potentiometer, a being ...
84 views

### Small signal model of current mirror

I'm trying to analyze the small signal model of this following snippet circuit (all the transistors are the same with beta = 100, and VA =100: What i've come up with is: simulate this circuit –...
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### MOSFET - Frequency response

I tried to do an exercise from my textbook where I have to discover the gain for mid frequencies of the MOSFET below, but I can't solve it. I got stuck at one point. I drew the small signal ...
92 views

### Relation between number of RC networks and phase shift in RC phase shift oscillator

The generalized expression for the frequency of oscillations produced by a RC phase-shift oscillator is given by the formula below $$f=\frac1{2\pi RC\sqrt{2N}}.$$ Here $N$ is the number of RC ...
• 13
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### Small signal output impedance for a circuit with bipolar transistor?

For the following circuit, I need to find the small-signal impedance looking into the collector of the transistor at terminal X, not taking the load resistance Z into account: My attempt at a SSM is: ...
• 141
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### Amplifying a pyranometer's small output using a single-supply amplifier

I am making use of theApogee SP-110-SS Pyranometer which outputs 0.2 mV per Wm-2. This pyranometer gives its true output over two cables, described as a positive and a negative output, where the mV ...
1 vote
42 views

### Difference AC signal and small signal / DC Signal and Operation Point

What is exactly the difference between an ac signal and a small signal? Or analogue between a dc signal and operation point. I've understood ac signal as a signal with a frequency > 0 Hz and dc as ...
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### Output Resistance BJT regarding Early Effect

I have a doubt respecting how to calculate the output resistance on this question below. I've searched at 4 different books and find the same way to compute this value but seems its not be right in ...
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### Source resistor in NMOS small-signal model

How does source resistance manifest in the small-signal model for NMOS transistors? I've come across two conflicting models for this case: the first seems to ignore the source resistance and neglect ...
1 vote
59 views

### Unsure about the correct application of Miller's Theorem

Sorry for the long post but I figured it would be easier to include pictures and all relevant calculations so that there wouldn't be any confusion. I have a circuit for which I'm trying to analyse and ...
• 105
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### Re model for Collector feedback bias with emitter resistance

For the given NPN transistor with $\beta=99$ and $r_e=0.02 k\Omega$, I need to find the voltage gain using Small signal Analysis. I drew the equivalent $r_e$ model as below. To find the Voltage ...
141 views

### Small signal analysis of MOSFET circuit

The other day I got the following exercise on one of my exams: For those who don't speak German, for transistor 1 lambda is 0, but not for the others. The backgate-effekt should be neglected ...
1 vote
168 views

### How is the AC equivalent drawn?

Fig. (b) is the AC equivalent of Fig. (a). I am not sure if this is right. Why is $r_e'$ grounded?
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### Perturbation and linearization for boost converter

I'm developing a boost converter (runs with DCM, and has $n$ turns ratio transformer) for uni which controls the input voltage with a constant output voltage. I'm at loss on how to get the transfer ...
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1 vote
128 views

### Calculation of power dissipation of a MOSFET circuit

As a part of an assignment to design a common source amplifier, I came up with this circuit: simulate this circuit – Schematic created using CircuitLab The transistor is a 180nm technology with ...
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### Bipolar high-dynamic range current sensing

I'm working on a project that will necessitate bipolar current measurement across a wide current range. It will need to accurately measure current from 750 mA down to 1 nA, although greater. The ...
93 views

### how to find gain of this complicated circuit?

I am having trouble with the following circuit. This circuit is AC model of Colpitts oscillator designed with NPN type BJT transistor. I am trying to find loop gain and check if it meets Barkhausen ...
91 views

### Equivalent resistance in BJT small-signal : Rpi in parallel with Beta*Ib

I'm currently reading Vorperian's book on Fast Analytical Circuits techniques. On page 129 he states : I'm not sure I understand correctly the statement I highlighted in yellow. Is it some kind of ...
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1 vote