Questions tagged [small-signal]

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78 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 ...
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1answer
45 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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1answer
46 views

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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1answer
67 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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1answer
49 views

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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29 views

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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2answers
75 views

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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1answer
64 views

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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1answer
96 views

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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3answers
125 views

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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3answers
107 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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1answer
58 views

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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41 views

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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119 views

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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0answers
41 views

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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0answers
41 views

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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49 views

Confusion with Norton's equivalent

I was trying to find Norton's equivalent for the following circuit from A to B: So I decided to start by using the fact that \$R_{th}=V_{OC}/I_{SC}\$, and found out that \$V_{OC}=0\$ so I decided to ...
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1answer
89 views

How do I get a KCL equation involving Vin in this circuit?

simulate this circuit – Schematic created using CircuitLab I've been scratching my head with this one. The circuit below is a small signal equivalent circuit of a PNP CB amplifier. I'm trying to ...
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1answer
94 views

Small signal Forward converter

I am back again on this subject. I found the control to output transfer function (Iout/Vc) of my forward converter (current mode) which is particular as it is without output capacitor. Actually it is ...
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1answer
56 views

What is the control Input of the small signal current mode PWM switch

I am trying to simulate the open loop transfer function of my system. My system is really classic. A converter (the plant transfer function), a sensor and a corrector which is a simple Integrator (1/(...
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1answer
398 views

Adding a Delay Ltspice

Is it possible to set a delay between two components on Ltspice ? Actually I just want to simulate the time for a sensor it takes to react (set an output) to an exciting signal. This is for taking ...
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0answers
43 views

Why is this small signal model incorrect?

Here is the model I was told to redraw by replacing the transistors with their mid frequency small signal model: And here is my attempt at doing so: Upon receiving feedback, I was informed that the ...
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0answers
32 views

How to get the minimum transconductance of a BJT ce amplifier?

We are being asked to bias a ce ampilifier circuit above to a gain of 15. It is given that the DC supply voltage is 10 V and a Vce,sat = 0.3V. Assuming that ro >> Rl >> Rload (on Vout when ...
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1answer
98 views

Small signal model of a forward converter operating in current mode control

By knowing that I do not know the plant transfer function of the forward converter operating in current mode control, I can be suspicious on the result provided by the following document : https://...
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61 views

Missing information when calculating impedance via Blackman's theorem

The AC course at my university has an ex-exam question where, in the below circuit, the impedance w.r.t. ground has to be calculated for the rightmost node. The question asks to do this using a test ...
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87 views

how to find Vout/Vin in this circuit? BJT frequency response

I have been struggling for 1 hour trying to relate Vout to Vin. However, I truly cannot. I tried KVL, node analysis etc everything that I could. Can you help me pls? The topic is frequency response of ...
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52 views

Where does this resistor appear in my nodal analysis? [BJT small signal analysis]

Here is my small signal circuit of a PNP common base amplifier with a resistor Rin at the emitter, Rl at the collector and a voltage source Vb at the base. Here is my large signal circuit: simulate ...
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42 views

Small signal gain

I'm struggling to find the small signal gain of the circuit shown below. I am trying to find the gain from Vout to Va. Note that Vout corresponds to the output of an amplifier. Any help is much ...
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4answers
280 views

Why does a circuit model of N-MOSFET exhibit a finite resistance between source and gate?

In the T-equivalent circuit model of a MOSFET in small signal analysis the MOSFET shows an infinite resistance between its gate and source when looking from the gate while it shows very little ...
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1answer
71 views

Small signal analysis of BJT dynamic microphone preamplifier

I am trying to do a small signal analysis for the following circuit I did not have any experience with BJT so I am having a hard time to analyze the circuit. From research, I know Q1 is common base ...
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1answer
88 views

Small signal analysis of dynamic microphone preamplifier circuit

I am trying to do a small signal analysis for a dynamic microphone preamplifier circuit. The original circuit is using BJT but I did not have much experiences with BJT, so I switched all BJT to MOSFET....
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62 views

short circuit time constants method (SCTC)

Why does the short circuit time constants method (SCTC) apply to large valued capacitances used for coupling or bypass purposes in a small-signal amplifier?
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1answer
263 views

Derivation of Feedforward Gains for current mode control in CCM converter

I recently start to read the dissertation of Dr.Ridley, A New Small-Signal Model for Current-Mode Control and I am stuck on a basic equation. First we have the function of the inductor current for ...
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3answers
156 views

Art of Electronics 2nd edition p. 67, figure 2.8 — what causes the clipping?

I have been rereading this section and realized I always get hung up here. The idea of clipping happening because the emitter is not able to stay .6 or so volts less positive than the base is ...
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5answers
124 views

Why does the feedback mechanism linearize the vi vs vo characteristic curve?

For a unity gain configuration opamp, we arrived at the conclusion that vout = vi * A/(A+1) by using small signal analysis, since A here is the small signal open loop gain. My question is: Why does ...
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1answer
211 views

How does the Common Emitter amplifier ensure low distortion?

My understanding of a small-signal amplifier is very limited. From what i've understood from this article is that for a BJT in the CE configuration, it provides minimal distortion at the output, I ...
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132 views

Small signal analysis - Flyback transfer function - LTspice

I am trying to simulate the transfer function of a Flyback by using LTspice. The flyback that I am trying to simulate is a flyback which can be found into the book "Switch mode power supplies&...
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1answer
71 views

What is RB in this CE circuit?

I'm working through this handout I3.PDF to help me understand feedback in common emitter amplifiers. (The author does not reveal his/her name in the PDF and so I can't ask them directly.) They show ...
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1answer
96 views

Optocoupler ac model ltspice

I am trying to plot the bode diagram of a flyback converter on LTspice. This is the first time that I do this and before trying to plot my flyback converter, I would like to plot the bode diagramm of ...
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1answer
77 views

Op Amp Selection Help for Rail/ Rail IO

I am looking for an operational amplifier which will fit my requirements. My circuit consists of two cascaded non-inverting amplifiers.I have a classical non-inverting setup.The minus pin of both ...
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2answers
35 views

Can I produce small signal gate-source voltage by applying small signal source-drain current?

As stated in the title, Can I produce small signal gate-source voltage by applying small signal source-drain current? There is no doubt that I can produce Ids by applying vgs, what about the other way ...
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1answer
82 views

Degenerated common source output resistance by inspection

In Razavi's Design of Analog CMOS Integrated Circuits (2nd edition), on page 65 he describes a way to derive the output resistance of a source-degenerated CS stage by inspection: I understand how to ...
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1answer
96 views

Solving a simple single-ended differential amplifier

simulate this circuit – Schematic created using CircuitLab N.B. I_D=KVov^2 without the 2 I’m really confused with this excercise, my problem is to calculate the A_v=v_out/vd and the cutting ...
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1answer
159 views

Why does a Darlington pair have a higher input impedance compared to a regular normal BJT transistor?

Freshman here, and I've been searching for an answer to this question, but I could not find any actual justifications yet. Basically, I am studying the concepts of a Darlington circuit, and saw that ...
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0answers
230 views

Degenerated Differential Pair voltage headroom

I was reading about ways to make the differential gain linear by adding degenerative resistors Rs as shown, but it has voltage swing limitations, having swing reduced by Is*Rs( when one of the MOS ...
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0answers
60 views

BJT Amplifier Circuit Analysis Feedback

I've been reading up on small signal analysis to try and better understand audio amplifier circuit design (end goal a discrete BJT guitar amplifier). I'm attempting to apply the knowledge I've picked ...
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0answers
96 views

Basic MOSFET small signal model with no load and Rd

I've come across the most basic small signal model of the MOSFET. We have a NMOS whose drain is connected to Vdd= 5V and source is grounded. We also have biased gate with a DC 2V. Suppose the ...
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1answer
190 views

Charge, Voltage, or Current? What can be measured with the highest SNR?

Suppose I have a Faraday cup and a certain number of ions hit the detector. What is the highest signal to noise ratio way / circuit to measure this... does one measure the charge (coulombmeter), ...
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2answers
191 views

Z(out) for small signal analysis with BJT for unbypassed emitter and r0 in place

from this BJT small signal I try to solve Z(out) but I find RC || (ro + RE) because Z(out) is calculated with ib = 0 => beta ib = 0 from this link too V(in) was calculated But the expression for ...
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4answers
97 views

Proof of linearity of a transistor

When we deal with a transistor we break it up into two parts, 1 The DC bias. 2 The small signal perturbations. Then we add the currents/voltages from the both the analysis to get the total response. ...