# 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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### Small signal model of buck converter

I want to find the transient response of an open loop buck converter for a step change in load current. To obtain the output impedance Zo = vo/io, which would help me to find the transient response of ...
70 views

### Return/Ground signal between SMA output

I am designing a IRIG-B AM modulated circuit. IRIG-B output signal will eventually be connected to another box (takes my IRIG-B signal as an output) through a wire (probably more than 4 feet). ...
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### Effect of GBW and slew rate for "small signal"

I would like to better understand how to choose an op amp for high speed application and more precisely I would like to better understand how the GBW and the slew rate influence the transient response/...
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### AC analysis of SMPS shows instability. How to modify the analysis to reflect the transient stability?

Background I have designed a switch-mode power stage with voltage-mode control that uses an LCLC filter in its output to obtain a very low ripple output voltage. I have empirically arrived at a ...
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### How do the stages of this high pass filter work?

I am trying to understand exactly how the stages of this Moog high-pass filter work but I still have several things that I cannot quite figure out: Q13 and Q14 form a push-pull amplifier, and are ...
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### BJT amplifier: small-signal analysis using H-parameters

I'm preparing for an exam and I have this problem where I need to find the input resistance as it is seen by the voltage generator ug. After using H-parameters to find an equivalent circuit I came up ...
111 views

I am trying to draw the small signal model of this circuit. I am not sure if it is correct that I connected VB (Vbias) to the ground in the small signal model since it is a supply voltage (please ...
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### MOSFET with resistor degeneration (Rs)

This is the two-port equivalent circuit of a CE amplifier with resistor degeneration (circuit 1). Will this just be the same in a MOSFET? What if the ro is approaching infinity in the MOSFET, is the ...
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86 views

### Why do JFETs have such wide parameter spread?

I've noticed that in almost every JFET datasheet I've looked at, the values for Idss and Vto (also known as Vgs-off vary hugely. A J111, for example, could have a Vto of anywhere from −3 to −10 volts ...
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### How to calculate small signal gain with LTspice?

For my homework I need to find the small signal gains of the circuit below. For the first part of the circuit the small signal gain is calculated with $$A_{V1} = \frac{u_{a1}}{u_e}$$ and for all of ...
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1 vote
112 views

### Can you explain intuitively why the pole exists in this common-emitter circuit?

This shows mathematically that common emitter circuit with the bypass capacitor $C_e$ has a pole. Can you explain intuitively why the pole exists here?
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### How to calculate the Output Impedance of RoT1?

I am a student, and I want to calculate the small-signal analysis, but I don't really know what's the formula of RoT1 (being a degenerated common base with RoT1 in the collector).
1k views

### Why is the frequency response of an LED important?

I'm working on visible light communication where I fabricate my own organic LEDs. One of the ways to characterize them is "small signal analysis." I understand we are applying this analysis ...
1 vote
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### Definition of small-signal capacitances calculated by Sentaurus TCAD Mixed-Mode/AC Analysis

I'm currently working on a capacitance model which will be part of a greater compact model for a planar RFET. I use Sentaurus TCAD to generate capacitance data, which I use to understand the ...
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### Small circuit analysis, DC voltage source short circuit or ground?

To convert a BJT into a short circuit we know that all DC voltage sources are short circuited. Yet my professor did this: Isn't this a contradiction? I just can't grasp the step.
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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 ...
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1 vote
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### 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 ...
191 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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253 views

### 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 ...
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### 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
86 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 ...
173 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 ...
219 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 ...
128 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 ...
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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: ...
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66 views

### 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
66 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
62 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 ...
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421 views

### 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 ...
169 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
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### 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
245 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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### How to find the output impedance for the unbypassed Common-Emitter Emitter bias configuration when ro presents?

I have found an equation in the book of Boylestad, but that equation is not matching with the equation which one gave solve for this type of question previously. Z_o=R_c \parallel \left[r_o+ \frac{\...
41 views

### Cannot obtain a generalized state space averaged model for simple wireless power transfer system

this is the first time I ask a question. I am currently working on finding a state space model of the following system : where $U_i$ is a square wave of amplitude $U_{in}$. This circuit ...
76 views

### Modelling Biased APD In Integrator Circuit

I want to model a biased APD (Avalanche Photodiode) whose current output feeds into an integrator. For the IC I will be using, TI recommends the following configuration for an unbiased photodiode. ...
378 views

### What is DC small-signal transfer function?

Can someone please explain to me what is the DC small-signal transfer function? I found this analysis type in LTSpice and I have no idea what it does! My guess: It linearizes the circuit around the ...
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1 vote
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### Amplification and bias point

I'm completely new to microelectronics, so please be forgiving. Let's say I have the following circuit: I have two fundamental questions: Can the amplified voltage exceed the power supply voltages ...
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### What is the difference between large signal model/analysis and dc model/analysis? [closed]

I am studying microelectronics. I have studied about the DC analysis and the AC analysis. The DC analysis is just to find the operating point or the quiescent point and then the AC analysis is done. ...
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### Small signal model of circuit with Darlington pair and source follower

I have some issues with drawing the small signal model of the circuit (picture 1.) I get confused when there are multiple transistors, especially when they are linked together like the Darlington pair....
627 views

### Small Signals and Large Signals Terminology: Models and Amplifiers

I am studying microelectronics. I recently got confused about about the small signal models and large signal models. After reading an extensive list of sources, I have come up with some pointers which ...
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