# Questions tagged [small-signal]

A circuit analysis method in which non-linear elements are replaced with linear elements whose parameters are determined by a linear approximation of the non-linear element's characteristic curve near its bias point. The result is an equivalent circuit that is a good approximation of the original circuit for signals small enough that the non-linear elements behave linearly (hence the name "small signal").

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### Superposition principle and Small signal analysis

first of all the superposition principle states that $$[ f(ax_1 + bx_2) = af(x_1) + bf(x_2) ]$$ and this apply to all linear element like resistor and capacitor because if we considered the current to ...
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### Question about drawing the small-signal equivalent circuit of an amplifier exercise

From Razavi's Fundamentals of Microelectronics book: I don't understand where did this ground come from? The resistor r_pi2 is connected between the emitter and base and then the base is grounded (...
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### Help Needed with Compact Circuit Design for Pulse-Triggered Switch-Off Sequence

I am currently working on a small electronics project for my swimming club and could use some advice. Forgive me if this is basic, I'm really new to electronics. The project requires a compact circuit ...
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### 3 phase emi filter for analog signal

I'm developing a device that needs to read analog data from a sensor located far away (~ tens of meters). To eliminate conducted noise (150 kHz..80 MHz) I use a ferrite filter on the cable and ground ...
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### Resistance in the small signal model of a MOSFET

I have a question about the small signal model of MOSFET. As you know there is a voltage-controlled current source in the model. I've seen somewhere in books that we can replace it with a resistor ...
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### Switching circuit with logic 3.3V control on p-channel JFET

The task is to derive sinewave (of higher frequency) chopped by step-function (also periodic but of lower frequency, i.e. several periods of sine wave are placed in that pulse). So I have a sinewave ...
I have a book that contains the solutions to certain problems that states that the small signal model for this circuit: is this: I don't understand it. Why is $Z_L$ in parallel with the VCVS $... • 1,259 1 vote 1 answer 75 views ### What is the difference between a BJT's DC and AC gain and why are they different [closed] Could you please explain what is the difference between the DC and AC gain of a BJT and why is the gain different for DC and AC? Where would the different gains be used? 0 votes 1 answer 54 views ### Is the bulk grounded in small AC signal analysis? This the circuit. The bulk is connected to ground in DC. Is the bulk grounded in small AC signal analysis (Vb = 0)? How about for PMOS? When the bulk of PMOS is connected to VDD, is the bulk grounded ... • 923 0 votes 0 answers 58 views ### For a degenerated CS amp with current mirror would the small signal model include the current mirror I am aiming to create an actively loaded degenerated CS amplifier and analyse the small signal performance in relation to maximum signal levels, maximum signal swing, voltage headroom requirements, ... • 21 1 vote 1 answer 108 views ### Differential output resistance with LTSpice I have a simple NMOS FET where I would like to plot the differential output resistance at the operating point of Vgs = 1.7V (which is the Vgs voltage for Id=9.4mA) I managed to plot the output ... • 7,705 1 vote 0 answers 42 views ### MOSFET small signal model question Why is vgs = vin - vout as stated in the image? The book has gmvGS wrong as it's supposed to be a current source. 0 votes 0 answers 112 views ### How to draw the small signal equivalent of this circuit? I need to convert this circuit into a small signal circuit but I am having a hard time drawing it. I think it is wrong at the FET-transistor connection to the bipolar-transistor. 1 vote 0 answers 71 views ### If I want to limit the bandwidth of this BJT to 10 kHz, what resistance should I consider when need to calculate the value of capacitor Cf? My wish is to get the capacitance value by calculating R when I use the hybrid-pi model, so use the formula Cf = 1 / (2 * pi * f * R). I would like to ask if the R value needed to use in the above ... • 29 7 votes 7 answers 4k views ### Why are capacitors treated as shorts in small signal models? If I understand correctly, a small signal model (e.g. hybrid pi modal of MOSFETs) is just a linear approximation of a nonlinear circuit centered at the DC bias point. At DC, ideal capacitors act like ... 0 votes 2 answers 139 views ### Minimizing small signal relay bypass pop Attached is a stripped down version of the circuit. The relay is controlled by a push button going to a microprocessor then powered by a BJT with a flyback diode in parallel. The output of the DSP/etc.... 1 vote 1 answer 232 views ### Circuit Analysis - Diode Small Signal Voltage I'm struggling with this circuit analysis about a pn-junction diode. I'm given I_D = 1.066 * 10^-7 A when V_D = 0.6V and I_D = 2.2 * 10^-5 A when V_D = 0.8V (all at room temp). My calculated values ... 0 votes 0 answers 145 views ### What is the standard form for writing the second order transfer function for Input impedance? When writing the transfer function for a system, the Characteristic equation in the denominator which carries information about the poles of the system is equated with the standard second order ... 0 votes 1 answer 348 views ### Does signal source of mobile phone, from its 3.5mm headphone jack, act as a current source or as a voltage source? Even though the audio output of the mobile phone (which we draw through 3.5 mm jack) outputs a signal that's a function of time, at a very short interval of time, this source acts as a dc source of ... • 31 2 votes 1 answer 342 views ### Small Signal Model of Two-Switch Forward - Basso I've designed a two-switch forward converter, that I would like to create a small signal model for to examine the stability criteria of the converter and then compatibility with the EMI filter... A ... 0 votes 1 answer 495 views ### Cascaded BJT Amplifier I found this circuit in here. I know that it's a multi-stage cascaded BJT Amplifier and I know how to calculate it. My question is, what R8 is used for? And If I remove it, is it cause any problem or ... • 103 0 votes 1 answer 175 views ### Thevenins equivalent resistance with only dependent sources What is the Rth of the below circuit Given R=R1=R2=10 ohms and g=10 siemens. Below is my solution.I am getting a value of 0.2 Ohms for Rth.May I know is this correct. • 2,595 0 votes 1 answer 132 views ### Finding transconductace Gm=Isc/Vin for a common source MOS amplfier with source degeneration I am looking to find short circuit current over input voltage to find transconductance Gm for a common source amplifier with source degeneration. To do this, I first shorted the output terminal and ... • 83 0 votes 4 answers 142 views ### How to give small voltage signal to Arduino? I have a device which audibly says a specific line, let's say it says "received payment of 5," and the device has a speaker connected. Now I want when it says this line, my Arduino should ... 0 votes 1 answer 99 views ### Calculating frequency response of a RF tuned collector amplifier I am doing a frequency response analysis for the following RF tuned circuit. I am not sure if I have done the right calculations so please correct me if there is any mistake. The DC equivalent ... 0 votes 0 answers 47 views ### Theoretical calculation of gate delay I am currently working on not-gate based ring oscillators and I was wondering if there was a way to theoretically calculate without having to look at the simulation graphs the rise time and fall time ... • 21 1 vote 1 answer 109 views ### Common Emitter small signal model for high frequencies simplification While trying to calculate the high frequency pole frequency corner of the common emitter amplifier I came across the following small signal model (found here in page 332) The small signal equivalent ... • 11 0 votes 1 answer 121 views ### Can I do AC analysis of a transistor solely using the input/output impedances provided by the datasheet? I learned to do AC small signal analysis of a BJT transistor with dV/dI ~ re = 26mV/Ie. But I don't understand why we take Vbe as 26mV here. Also, in the datasheets, I found graphs of input/output ... • 288 1 vote 1 answer 52 views ### Would more connectors introduce more noise for low-frequency current signal? General question When measuring the weak amplitute low-frequency (DC) current signal (in 0.1 - 1 uA) transmitted through FFC cable and connectors to a PCB with transimpedance amplifier (TIA) and ADC, ... • 232 1 vote 3 answers 161 views ### Output impedance of small-signal model When I calculate the output impedance (Rout) of this small signal model, do I have to short circuit between 2 ends of the blue wire or black wire? 3 votes 2 answers 309 views ### How feedback loop is done in wide voltage range laboratory power supply? TL494 compensation Hello i would like to ask how is compensation done on switching PSU with wide range variable output voltage (from zero to several hundres of volts). I have succesfuly (I guess) simulate my own design ... • 135 1 vote 1 answer 108 views ### Transfer function of a system regulating current Here is the circuit with two different MOSFETs : The circuit controls the current through the resistors R3 or R1 via a reference voltage (V1 and V3). As you can see there is an inductor. I plot the ... • 2,478 1 vote 1 answer 552 views ### Small signal model of buck converter I want to find the transient response of an open loop buck converter for a step change in load current. To obtain the output impedance Zo = vo/io, which would help me to find the transient response of ... 2 votes 2 answers 471 views ### Return/Ground signal between SMA output I am designing a IRIG-B AM modulated circuit. IRIG-B output signal will eventually be connected to another box (takes my IRIG-B signal as an output) through a wire (probably more than 4 feet). ... • 133 1 vote 2 answers 246 views ### Effect of GBW and slew rate for "small signal" I would like to better understand how to choose an op amp for high speed application and more precisely I would like to better understand how the GBW and the slew rate influence the transient response/... • 2,478 2 votes 0 answers 173 views ### AC analysis of SMPS shows instability. How to modify the analysis to reflect the transient stability? Background I have designed a switch-mode power stage with voltage-mode control that uses an LCLC filter in its output to obtain a very low ripple output voltage. I have empirically arrived at a ... • 22.5k 0 votes 2 answers 94 views ### How do the stages of this high pass filter work? I am trying to understand exactly how the stages of this Moog high-pass filter work but I still have several things that I cannot quite figure out: Q13 and Q14 form a push-pull amplifier, and are ... • 101 0 votes 3 answers 230 views ### BJT amplifier: small-signal analysis using H-parameters I'm preparing for an exam and I have this problem where I need to find the input resistance as it is seen by the voltage generator ug. After using H-parameters to find an equivalent circuit I came up ... 0 votes 1 answer 941 views ### Please help me draw the small signal model of this circuit I am trying to draw the small signal model of this circuit. I am not sure if it is correct that I connected VB (Vbias) to the ground in the small signal model since it is a supply voltage (please ... • 35 4 votes 1 answer 168 views ### Why do JFETs have such wide parameter spread? I've noticed that in almost every JFET datasheet I've looked at, the values for Idss and Vto (also known as Vgs-off vary hugely. A J111, for example, could have a Vto of anywhere from −3 to −10 volts ... 2 votes 1 answer 4k views ### How to calculate small signal gain with LTspice? For my homework I need to find the small signal gains of the circuit below. For the first part of the circuit the small signal gain is calculated with A_{V1} = \frac{u_{a1}}{u_e} and for all of ... • 35 1 vote 2 answers 246 views ### Can you explain intuitively why the pole exists in this common-emitter circuit? This shows mathematically that common emitter circuit with the bypass capacitor$C_e$has a pole. Can you explain intuitively why the pole exists here? • 698 0 votes 0 answers 39 views ### How to calculate the Output Impedance of RoT1? I am a student, and I want to calculate the small-signal analysis, but I don't really know what's the formula of RoT1 (being a degenerated common base with RoT1 in the collector). 4 votes 5 answers 2k views ### Why is the frequency response of an LED important? I'm working on visible light communication where I fabricate my own organic LEDs. One of the ways to characterize them is "small signal analysis." I understand we are applying this analysis ... 1 vote 1 answer 276 views ### Definition of small-signal capacitances calculated by Sentaurus TCAD Mixed-Mode/AC Analysis I'm currently working on a capacitance model which will be part of a greater compact model for a planar RFET. I use Sentaurus TCAD to generate capacitance data, which I use to understand the ... • 11 1 vote 2 answers 689 views ### Small circuit analysis, DC voltage source short circuit or ground? To convert a BJT into a short circuit we know that all DC voltage sources are short circuited. Yet my professor did this: Isn't this a contradiction? I just can't grasp the step. • 11 0 votes 0 answers 94 views ### Series capacitor buck converter small signal model Does anyone know how to do the small signal model of the series capacitor buck converter? I can't find a related paper talking about this one. I think the small signal model is not the same as the ... • 357 2 votes 1 answer 102 views ### Is there a typo in this question because I don't think the emitter node of Q2 should be grounded? In this problem, it's asking us to draw the small signal equivalent of an amplifier but I think the answer they gave is wrong. In the second picture (b) I don't think the emitter of Q2 should be ... • 165 1 vote 1 answer 187 views ### Small-signal of CS stage with source degeneration Can someone explain how Fig 3.30 (c) was created? In particular, the$\large\frac{1}{g_m + g_{mb}}$resistor to GND. I know you see$\large\frac{1}{g_m + g_{mb}}\\$ when looking into the source, but ...
I am trying to have a small signal analysis of a Wilson BJT current mirror to find out what is the output impedance. Already I know that the answer is $$R_o=\beta r_o/2$$ In the first step, I need to ...