# Questions tagged [small-signal]

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59 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 ...
30 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 ...
39 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 ...
72 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 ...
44 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 ...
54 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 ...
52 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 ...
65 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 ...
173 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), ...
70 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 ...
26 views

### BJT Hre simulation problem

im having problems understanding the behavour of the hybrid parameter hre in the bjt AC model. im using the pi equivalent circuit to simulate the relation between hre and Ic (Dc value). i am not ...
85 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. ...
37 views

### What is the difference between DC base current and signal current in CE transistor amplifier?

I came across a sentence that " if the DC base current has to be 10 times the signal current....".I could not understand, what is DC base current as I have just read about Input current and Output ...
40 views

### Base current in a npn transistor in view of its small signal model

We know that in a forward biased transistor we have βIb = Ic. However in the model it's clear that the above equality doesn't hold, we now have Ic > β.Ib. What's wrong in my understanding of the ...
36 views

### Input and Output Resistance of an Amplifier

I attempted to find the input resistance by using the thevenin equivalent circuit. I shorted all the capacitors and changed the circuit to its small signal equivalent. I found Rb to be 13.33kOhms ...
43 views

### re model of transistor

In which case shall I consider output resistance(ro)? I found that in case of re model for common emitter configuration we are considering output resistance(ro) but there is no (ro) in emitter ...
135 views

### Do capacitors and inductors have initial voltage or current in small signal approximation problems?

I'm trying to solve a small signal approximation problem. The operating voltage for the capacitor is 2 volts. I simplified capacitor by a linear one. In solving this problem should I consider the ...
65 views

### is this small signal equivalent circuit of mosfet amplifier correct?

We are given an assigment about mosfet common source amplifiers and we are given this circuit. I drew its small signal equivalent circuit but I am so unsure about placement of ro(transistor resistor). ...
4k views

### mV variations even with a simple voltage divider

edit: After using a prototype pcb instead of breadboard, placing all possible electromagnetic sources away and unplugging all the equipment from the same line, my noise dropped 2 orders of magnitude. ...
29 views

### Where does the input resistance formula of a BJT amplifier come from?

I just solved the (a) question of this problem from one of my past exams. And I am a bit confused on to why the solution is as follows: Rin = 100kΩ || Rib Rib = (rπ + (1 + β)Re) And the way Rib is ...
21 views

### 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 ...
99 views

79 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 ...
77 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. ...
44 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 ...
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*...
26 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 ...
34 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? ...
72 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 ...
114 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 ...
218 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 ...
175 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 ...
78 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 ...
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 ...
36 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 ...
45 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 ...
61 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 ...
673 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 ...
138 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 ...
149 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 ...
223 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}+...
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 ...