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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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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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 ...
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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 ...
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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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3 answers
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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 ...
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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 ...
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1 answer
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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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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{\...
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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 ...
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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. ...
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2 answers
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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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3 answers
131 views

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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1 answer
159 views

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....
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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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BJT small-signal base resistor voltage

simulate this circuit – Schematic created using CircuitLab I am doing a small signal analysis of the following common-emitter BJT stage and I am trying to calculate the voltage across r_π (v_π). ...
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Define input impedance of a buck converter for ideal converter (efficiency 100%) & practical converter

What I know was -The input impedance by the closed-loop buck converter in CCM mode, Zi and, in turn, that presented impedance is dependent on Zo and the duty cycle used by the buck converter below is ...
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2 answers
351 views

Push Pull Output and Input Resistances

I'm reading Sedra's book on Microelectronics (7th edition, section 12.4.2), and in the chapter on Output Stages he calculates the Output Resistance of a Class AB Push Pull Amplifier. My problem is: he ...
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output resistance and transconductance in the calculation of NMOS common source voltage gain

For a NMOS, the transconductance gm is defined as id/vgs at a fixed VDS. However when we calculate the small signal gain of a common source amplifier, we use vds = -id x RD and then vds = -gm x vgs x ...
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3 answers
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Why are collector resistors grounded in AC small signal analysis of a differential amplifier?

Why are \$R_{C1}\$ and \$R_{C2}\$ grounded while doing small signal analysis?
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1 answer
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Are the AC resistances in the hybrid pi model and the T model of BJT the same?

I have been wondering if the AC resistances in the two models of BJT circuit mean the same thing, that is $$r_{c} = r_{c'}$$ $$r_{b} = r_{b'}$$ $$r_{ex} = r_{e'}$$ If they are different, please ...
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Gain of a Modified Common Gate Amplifier

I want to know how the gain of the amplifier shown below can be calculated. The gain turns out to be as shown, but why? I know that the gain of a common gate is gmRD, but is the circuit shown here a ...
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Measuring the amplitude of a nV signal of known frequency and phase using AD633

I am wondering if there is a circuit to measure the amplitude of a sinusoidal signal of known frequency and phase that is induced in a pickup coil. The amplitude would be in the range of 0nV to ...
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6 answers
366 views

Op amp is not amplifying a 2 mV signal

I trying to amplify an electrical signal created by electrodes on skin, which create a potential of around 2 mV. Therefore, I am using a LM324N operational amplifier (powered by 9 V battery) and ...
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1 answer
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Minimum Detectable Signal of Camera and Improvements to Minimum Detectable Signal through pulsing

My goal is to determine for specific signal measSig, what is the largest background signal backSig I could receive and still be able to detect my measurement Signal? I know that camera modules ...
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1 answer
137 views

Validity of small signal model during transient state

In most of the books it looks like small signal is used as a steady state analysis, for example a capacitor is modelled as: $$Xc=\frac{1}{j \omega C}$$ Which clearly indicates a steady state analysis. ...
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Input impedance of emitter follower

I decided to calculate the input impedance of the following emitter follower circuit as a practice. I used this well-known small signal model for the BJT: For voltage gain, I obtained $$A_\text{v}=\...
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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 ...
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need help with small load cell and ADC

I am working on a project where I should be able to measure as low as 1mg load change. The acceptable error margin would be 0.1 mg. I am planning to use load cell with total capacity less than 10g ...
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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 ...
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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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The load resistance in a MOSFET current mirror vs CMOS

In class I have learned that in a MOS current mirror like the one below, we can say that the load seen by M1 is equal to r_o of M2. This makes sense to me since I have drawn the small signal model and ...
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2 votes
1 answer
74 views

Buck-Boost small signal

I read the paper "Simplified Analysis of PWM Converters Using The Model of The PWM Switch", and I have some questions about the model of DCM (Discontinuous Conduction Mode) flyback. This is ...
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Small signal model of Boost DCM

I read the Christophe Basso APEC 2013 and on page 90 I have some questions: 1.) How to get equation 2, because I don't know where B1 current comes from. 2.) what is B1 current meaning
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MOSFET triode small-signal modeling

TL;DR: Why do seemingly all treatments of MOSFET small-signal operation ignore the nonzero \$g_m\$ contribution in triode? Is the implicit assumption here that if the MOSFET is operated in triode then ...
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2 answers
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What are the advantages and disadvantages of a Darlington pair? [closed]

Can the BJT transistors in a Darlington pair be of different types?What are the advantages and disadvantages of a Darlington pair? Is such a circuit able to generate power by itself?
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Small signal modelling of buck converter, varying frequency

It seems that the most popular method of voltage mode control of buck converters is by varying the duty cycle. Is this because it is easier to do so because we can set the duty cycle using PWM ICs? ...
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1 answer
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Voltage gain, input/output impedance using multisim.. How? [closed]

This is the picture of my amplifier circuit using multisim... But I'm not very familiar with this software and thus... how do I do the AC analysis to get the voltage gain, input/output impedance...?
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1 vote
3 answers
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BJT Common Emitter Output Resistance

Hello, I am attempting to determine the small signal output resistance \$R_o = v_x / i_x\$ of the Darlington pair common emitter's small signal model. I have written the equation KCL at node c, \$ i_x ...
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3 answers
209 views

Problem of transistor thermal runaway in parallel connection

simulate this circuit – Schematic created using CircuitLab I wanted to use two transistors in parallel to increase current rating. So I simply put two transistors in PCB design. Later I found ...
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1 answer
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Output Resistance of Small-Signal MOSFET Circuit

I have some doubts concerning the calculation of the small-signal output resistance of a common-source stage with source-degeneration. This is related to another question I posted but I have refined ...
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buck small signal modelling

I have a synchronous buck converter and my inductor current looks like this:- To add voltage-mode closed loop control, I need to do the small signal modelling of the converter. I am a bit confused if ...
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3 votes
0 answers
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Impact of PFC output impedance on the regulation of a converter

I have determined the transfer function of my converter operating in closed loop configuration. Nevertheless I saw on the web that the transfer function is not the same if my converter follows a PFC. ...
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Making an operational amplifier out of a differential pair

I need to modify this circuit to serve as an operational amplifier with low output resistance Because the operational amplifier that I'm familiar with uses this differential pair: I thought about ...
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Proving that we can apply the half-circuit model for the common-source differential amplifier

This is the circuit I'm trying to solve through the half-circuit model: To do so I need to first prove that \$V_{p}\$ is a small-signal ground under opposite symmetric excitation (\$v_{in1}=-v_{in2}\$...
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