# Questions tagged [small-signal]

The tag has no usage guidance.

41 questions
Filter by
Sorted by
Tagged with
49 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 ...
101 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 ...
99 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 ...
46 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 ...
67 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 ...
61 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 ...
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 ...
39 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 ...
53 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 ...
395 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 ...
90 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 ...
69 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 ...
94 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}+...
63 views

### Determining the output resistance of a BJT amplifier

I'm given the following amplifier: (all the transistors have the same characteristics; Early effect is neglected) In order to calculate $R_{out}$, we replace the circuit with its small-signal ...
71 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 ...
245 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 ...
112 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 ...
65 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 ...
98 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. ...
296 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 ...
129 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 ...
153 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?
202 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 ...
258 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.
156 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 >=...
73 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, ...
398 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 ...
176 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 ...
285 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, ...
117 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 ...
144 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?...
150 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 ...
137 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. ...
204 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 ...
47 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 ...
785 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 ...
1k views

### MOSFET amplifier mid-point bias

I have a simple MOSFET amplifier design and want to set Q1 drain to be one-half of VDD0 for mid-point biasing. It may be achieved by tuning during simulation with a variable resistor in divider R2-R3,...
108 views

### Power amplifier input source current path

Can anyone draw (or write in text) the small-signal path from signal source XFG1 at input of Q1 base to amplifier load for positive and negative input signal swing?
67 views

### Half of differential tage voltage gain

I can't understand why is 2Rpi in equation 375/376. It looks like the current ib1 goes through Rpi of first stage and through Rpi of second stage but it must go through first Rpi to ground and back to ...