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Questions tagged [small-signal]

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0answers
51 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 ...
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1answer
65 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
56 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
71 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
51 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
82 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
186 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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0answers
76 views

Input/out impedance and voltage gain

I've tried to look for answers over the internet and books but I haven't fully understood it yet! If I have a circuit like that one shown in the picture how can I calculate its small signal voltage ...
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1answer
85 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
118 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
137 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
214 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
91 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
58 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
220 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 ...
0
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0answers
91 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
252 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
95 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
96 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
127 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
90 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
181 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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0answers
88 views

Small Signal OTA Circuit

I am having some difficulty determining the constants \$a, b, k\$ in the open circuit voltage transfer function \$T(s) = v_0/v_i(s)\$, which is given by \$T(s) = k \frac{[s + a]}{[s + b]}\$ I know ...
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0answers
77 views

Small signal model of cmos amplifier

To get Vout/Vin, I made small signal equivalent circuit My question is this 1)Is the small signal equivalent circuit that I made correct? 2)How can I get Vo/Vin from the small signal model?
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1answer
40 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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0answers
536 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 ...
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2answers
883 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,...
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1answer
95 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?
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1answer
47 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 ...
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1answer
177 views

JFET Q-point for use it as resistor

I'm trying to use JFET as resistor. For use it as a resistor DS voltage need to be less than Vp. Vp from datasheet of 2n4391 is equal to -VgsOff and equal to 4.0V. How I can to set scheme to view ...
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3answers
133 views

When should the AC resistance of a diode be taken into account in a practical circuit?

In many circuit design examples I see the diode drop is taken constant value such as 700mV. And I also know that for amplification and small signals transistors are used as discrete components. Here ...