Questions tagged [small-signal]

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Differential Amplifier small signal analysis

I am having trouble doing the analysis the small signal model of this circuit: So far, I have come up with this this circuit for the small signal analysis: However, I can't come up with a formula ...
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2answers
86 views

MOSFET small signal model output resistance

I am wondering what is the output resistance of the circuit below. I found that it depends on the gate voltage: $$ \begin{aligned} R_{out} &= \frac{V_{out}}{I_{out}} \end{aligned} $$ $$ \begin{...
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36 views

Strange MOSFET Common-Source with RD=0

I was trying to solve this circuit(find the Q Point, voltage gain, input and output resistances in midband region, the lower cutoff frequency using SCTC method), but I was confused by the absence of ...
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2answers
52 views

Finding small signal resistance for MOSFET

I need to find the small signal parameter \$r_{D1}\$. I understand I must draw the small signal equivalent first, but I do not know where to label this resistance, or what exactly it is equal to. Also ...
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38 views

Amplifier \$I_c\$, \$V_{ce}\$ operating range

In the 10th edition of Electronic Devices from Thomas L. Floyd Example 6-1 provides a way to find the AC model output signal operating range based on the following circuit. I'd like to ask for a ...
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1answer
37 views

how to determine the small signal parameters of nMOSFET from Datasheet?

as I want to calculate the transfer function of circuit that is meant to generate source current using an Op amp as control loop, I need the gm and r0 of the mosfet(to determine the transfer function ...
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23 views

Finding input and output resistance of a small signal model

I found the small signal model for a common source amplifier, but I am having trouble finding \$R_i\$ and \$R_o\$. The question specifies not to include \$R_{sig}\$ nor \$R_L\$. I drew in green where ...
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1answer
42 views

Is placing the ground in this small signal model wrong?

There is an example in a text where it shows the small signal model of a circuit. Below on the left there is a transistor circuit and on the right its small signal equivalent: I'm a bit confused ...
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1answer
32 views

Deriving the small signal model of this transistor

Given that the current equation for a graphene transistor is given by equation (1) I'm trying to find the small signal model of the transistor. $$(1)\space \space i_D(V_{GS},V_{DS})=\frac{W}{L}μ(C_{...
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1answer
56 views

KVL equations for this small signal model

I could figure out how the small signal pi model is obtained from the large signal model and below shows an example circuit where I also draw the pi model: But from this point does KVL hold? How can ...
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51 views

Derivation of output impedance of emitter follower or common collector amplifier (using Thevenin's Theorem ?)

I was going through the AC equivalent circuit of Common Collector Amplifier from ELECTRONIC PRINCIPLES BY MALVINO 3RD EDITION and I came across the analysis for the output impedance of the circuit. ...
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29 views

Small Signal model of darlington pair with resistor

Im trying to create a small signal model of a circuit with a darlington pair in it. The circuit is the one in the image below. I have managed to do this small-signal model but i feel it is a little ...
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38 views

What is the small differential gain?

Circuit 1: is the original circuit, circuit 2: Half circuit, circuit 3: small signal model For this circuit we are assuming lambda=0 Our solution: Vin=Vgs1 Vout=-gm3*Vgs3*R1 Av=Vout/Vin=(-gm3*Vgs3*...
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25 views

Modeling small signal equivalent circuit of a transistor circuit

For this homework question, I have to model the circuit and find output impedance. The question states that the capacitors can be modeled as short circuits. As I think I understood it, the resistor ...
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1answer
27 views

Measuring input and output resistance of the hybrid model

I understand that the input and output resistance is calculated using the Thevenins theorem. Thus the output resistance = Rc itself as the current source is open. But what about input resistance? ...
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4answers
61 views

Small Signal quantities

Behzad Razavi in his book mentions It is important to bear in mind that small signal analysis deals with only (small) changes in voltages and currents around their quiescent values.... If the ...
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1answer
110 views

Am I applying the KCL the right way? [closed]

Applying KCL at the node where I have drawn the currents in order to find Vin/Vs, I am not getting the correct answer which however I did obtain using the Voltage Divider. My question is, am I using ...
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3answers
132 views

Why is this current source with both sides grounded still supplying current

Now if we write a node equation at \$C\$ we get \$I_C = g_m − sC_μ V_π \$ But my question is, is it correct, how do we define the current through the branch with \$g_mV_π \$ since both of its ...
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1answer
82 views

How to calculate small signal parameter for a BJT when early voltage is taken into consideration?

I have proved one formula of output impedance ro = (Va+Vce)/Ic = Va/Ic' where Ic is collector current and Ic' is collector current neglecting early effect. But reading from standard texts other ...
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0answers
71 views

Calculating the gain of a specific transistor amplifier circuit

NOTE: There is an error in the drawing above — C1 should be connected to the emitter, not the collector. Hi Electronics SE, hope this is the right place to ask this, if not I'll gladly take it ...
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1answer
63 views

What is the advantage of concatenating two nMOSFETs M1,M2 with Source of M1 connected to Gate of M2?

I am trying to understand the circuit in the figure here : I hope I analyzed correctly its gain (for small AC signal). My small-AC-signal-circuit is attached in the bottom of this post). However, I ...
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34 views

Circuit with both common source & common gate

I'm trying to calculate the following cirucit's voltage amplification \$A_v= \frac{V_{out2}}{V_{s2}}\$ using the known topologies of common source & common gate. On one hand, I can see that on ...
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41 views

Calculating the gain of a transistor in VGA

This paper is from IEEE: The gain of the first VGA is expressed as \$ A_1 = \frac{gm_1 R_1}{1+gm_1 R_2+\frac{R_2}{ro_1}} \$ However, I thought that since the (DC) current source at the source of ...
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57 views

Mosfet amplifier calculate small signal gain

I try to solve problems in textbook. There is an amplifier which is powered by a +Vs and -Vs power supply, The problem asks for small signal gain. According to solution manual solution for VIN is ...
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2answers
548 views

Why does the small signal analysis work? (Intuition)

Consider the Large and small signal model of the MOSFET amplifier, simulate this circuit – Schematic created using CircuitLab How is this transformation valid, I get the linearization of the ...
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0answers
114 views

Amplifier voltage gain

How to determine the voltage gain and input/output impedance of the following circuit given that R1=273.56 and R2=2325? I have been trying to calculate the voltage gain through solving small signal ac ...
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2answers
96 views

Step by step approach to the analysis of transistor circuits

Below we have a circuit cosisting of three transistors. Is there any systematic approach to the analysis of such circuits. We are asked to find the values of R1 and R2 and aslo the operating point of ...
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2answers
119 views

Find output impedance of BJT amplifier

I need to find the output impedance of the BJT amplifier as shown below: The equivalent small-signal circuit looks like the following: I know that the output impedance is $$Z_o=R_{E1}\ ||\ (R_{E2}+...
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1answer
78 views

Input resistance confusion

Here's a circuit of an amplifier in the CB configuration: The small-signal equivalent is (using hybrid-pi model) I want to calculate the input resistance \$R_{in}\$. If I'm not mistaken, the blue ...
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1answer
795 views

PNP BJT small signal model

I have been solving BJT circuits on my textbook and stumbled upon a PNP BJT small signal model question. It asks to build the small signal model of a PNP transistor circuit. When I checked the ...
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2answers
190 views

Gain of a feedback amplifier with base to collector resistor [closed]

I'm able to solve this problem using the concept of Miller resisitance however I'm having an issue solving this problem using the concept of feedback amplifiers. Can someone help me solve this problem ...
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1answer
66 views

How would I go about measuring an analog signal that has both positive and negative voltages on an arduino analog pin at a high sampling rate?

I have a signal that fluctuates between -70mV and 50mV. How would I get the arduino mega to read this on an analog pin at a high sampling rate? Ultimately I am trying to graph the data in real time so ...
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1answer
152 views

finding small R in series RLC circuit

Hello! I have an device which is equivalent circuit is RC as follows in the image I shared: R is supposed to be 0.5Ω and C supposed to be 30nF, but it can vary a little bit between device to device. ...
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1answer
428 views

Small signal equivalent circuit - MOSFET

Let's consider the following amplifier circuit: Now, if we would analyze small signal operation, we could represent the circuit with small signal equivalent: The part that bothers me is the PMOS ...
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1answer
156 views

circuit analysis for an amplifier

so I had my original circuit looking like below: simulate this circuit – Schematic created using CircuitLab I was able to simplify it to look like as follows: simulate this circuit but now ...
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2answers
284 views

If a MOSFET has infinite inner resistance (ro), how does current flow through it?

Ideally the MOSFET is a current source in saturation mode, but I don't understand why is it modeled with an (ideal) infinite inner resistance. How would the current flow?
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1answer
273 views

Common source amplifier, source degeneration and determining the cutoff frequency

I have a n-MOS transistor with the following biasing network: I have to determine the cutoff frequency due to GS and GD capacitances The method used by my book is to first redefine the ...
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3answers
355 views

What is small signal. And what is small signal equivalent circuit

I am very new in electronics. And this topic is bothering me. I want to know what is small signal and how to draw a small signal equivalent of jfet with common source.
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1answer
184 views

Designing a Class A Audio Amplifier

I am currently working on a project where I am required to design a Class A Audio Amplifier using BJTs. The requirement of the amplifier is as follows: - Acquire a variable gain of at least 10 (Av >=...
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1answer
74 views

Addition of step disturbance to a microgrid state space model

If we are having a microgrid model in the state space form as \$\dot{x} = Ax\$ where \$A\$ is complete system matrix.The matrix \$A\$ includes all the active power , reactive power, load currents, ...
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3answers
644 views

Is the hybrid-pi parameter hie really equivalent to (beta+1)*re?

I'm reading a book on feedback amplifiers at the moment and it makes comprehensive use of a simplified hybrid-pi model. A parameter that keeps popping up is hie and I've always considered this to be ...
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0answers
223 views

LNA using Common Emitter with feedback collector

I am trying to design an LNA with input impedance of 50 Ohms, I am considering the topology illustrated below. I have found an online calculator that computes this however when I try to work out the ...
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2answers
307 views

Finding Rout of differential pair with active current mirror (from Razavi's “Design of Analog CMOS Integrated Circuits 1st Edition”)

According to Razavi, \$R_{out}\$ is approximately \$r_{o2}||r_{o4}\$: I get the same answer (assuming \$2r_{02} >> \frac{1}{g_{m3}}||r_{o3}\$): But how did he get equation 5.27? In particular, ...
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1answer
130 views

Feedback MOSFET circuit anaylsis

I am having difficulty calculating the gain and input resistance of the circuit below. Neglecting ro, capacitance, and considering Ibias is ideal (infinite resistance), would this mean that the ...
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1answer
186 views

Power amplifier DC and AC current adding

Here is my simple power amplifier: I need an explanation how the summary DC+AC current will behave on Probe2 and on Probe3 for positive and negative voltage swing of the signal in the amplifier input?...
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1answer
168 views

What are the benefits of this type of JFET biasing

The next schemtaic I was found as an input stage of ultra-linear phono amplifier. What are the benefits of that type of biasing? I don't see that 12V zener has 12V voltage drop on it (only 4.2V) and ...
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1answer
217 views

CMOS source follower with 2 in series

I am really struggling with where to start to analyse this. Using the Shichman Hodges Model and the small signal equivalent circuit, the voltage gain can be equation can be seen to be vo = -gmvgsr0. ...
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3answers
238 views

AC Analysis of emitter circuit, why can I ignore resistance R1 but not Rc?

I am trying to calculate the small signal voltage gain of this circuit but I am having a problem comprehending the last step. I rewrote the circuit like this But the solution says this: Which would ...
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1answer
50 views

\$i_{b1}\$ in this simple bjt circuit

From Bartlett's bisection theorem. Common-node. So I don't get, shouldn't \$ i_{b1} \$ be: \$ \frac{V_{ic}}{r_\pi + 2 R_{ee} } \$ ? \$r_\pi\$ is in series with \$2 R_{ee}\$, so they have same ...
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889 views

Biasing one-stage MOSFET amplifier

I'm really discouraged with MOSFET amplifier biasing. The results of my experiements my be found here: MOSFET amplifier mid-point bias Voltage-divider schematic: I found that for voltage divider ...