Questions tagged [biasing]

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Emitter resistor and biasing voltage

In many articles regarding transistor biasing I see a circuit like below and I don't really get what is the point of biasing like this WITHOUT emitter resistor Re? When emitter branch is connected ...
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2answers
93 views

Howland current source with voltage reference [closed]

I need a precision current pump for small ac signals(50uA) and i tried it in multisim with a howland topology. It works however i need the load to not be grounded but bound to a bias voltage. Here i ...
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1answer
53 views

Why is the effective base resistance important for the voltage divider BJT amplifier?

I came across many questions regarding the below type of biasing where they explain and analyze Rth Vth and conclude that Rth must be very small comparing to Rin. Rin is the effective resistance seen ...
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4answers
87 views

What exactly is meant by beta dependence in this fixed bias BJT scheme? [duplicate]

What I understand that, in a fixed bias BJT scheme the problem is beta dependence. Below is an example from a text: Now I read that this is not a good design. But I will still solve this by assuming ...
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1answer
61 views

Bias voltage of transistor [closed]

I would like to understand the purpose of biasing the transistor and why It has to be halfway between Vcc and ground? And which terminal of the transistor (Base, collector or emitter) should be ...
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0answers
33 views

Is Q-Point in Transistor constant? For different configuration if same transistor is used?

Via IV-Characteristics, for specific Ib, I got the Q-Point and using the same value of the Q-Point, I constructed a common emitter configuration biasing circuit that its V_ce = Q-Point_Voltageafter ...
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1answer
55 views

Deriving that Vin is way larger than nVt from Shockley equation

I am trying to show that from the Shockley equation Vin >> nVt. Given a simple diode circuit like this So far, I have equated the current through the resistor \$I = \frac {V_{in} - V_{D1}} {R_1}\$ ...
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0answers
39 views

Biasing an Enhancement NMOS with Gate-Source Connected

I'm working on a university project wherein a full-wave rectifier is constructed using two enhancement mode NMOS transistors. I'm tasked with designing a biasing circuit for the NMOS', but I don't ...
0
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1answer
38 views

Confusion regarding Fixed-Biased configuration of JFET

This is the picture of a fixed-biased JFET, taken from a book :- This is written in the book, relating to the above pic :- I am unable to understand why \$ V_{GS} \$ has a different polarity than \$ ...
0
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1answer
86 views

Voltage Divider Configuration of Transistor

I have a voltage divider configuration for biasing my transistor. The gain of transistor is lets say 150 which is typical value for BC547. What I want is limit the current flowing through the base to ...
1
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2answers
72 views

Why is Rc parallel to RL?

While determing the AC load line, the author takes Rc to be parallel to Rl. How is it possible since the two resistors have different nodes?
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0answers
37 views

Voltage Gain for Driver in Class AB Amplifier

Can anyone tell me how to calculate the Voltage gain for Q3 in the following schematic ? Is it the same method (or partially modified) like the one used for Class A amplifiers for Voltage gain ...
0
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1answer
72 views

Biasing in this FM transmitter

Here is a simple FM transmitter that I've been studying recently. What I'm wondering about currently is how the BJT amplifier in this circuit is biased. I believe that from the audio signal standpoint ...
0
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1answer
45 views

Amplifier Voltage

I'm studying for my electronics exam and for this particular problem I have: Av = –85 (V/V), Ap 21 (dB) power gain, Ap = 3.41 (W/W), L+ = +9 (V), L- = -6 (V). Now the next exercise asks that: ...
0
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1answer
51 views

Transistor Biasing of high side switching network for PWM control

simulate this circuit – Schematic created using CircuitLab iagramI am attempting to create a high side switching circuit for a string of LEDs wired in parallel. There are multiple strings, all ...
1
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2answers
497 views

Biasing a second stage amplifier

I built a two-stage amplifier as shown below. I have already built the first satge (R1-R5 & C1-C2) such that If I apply a signal of 1volts peak-peak, the output (at collector of Q1) would be 8 ...
0
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1answer
120 views

What's the purpose of the inductor in this microphone biasing schematic?

I'm just wondering what's the purpose of the inductor in this microphone biasing schematic? Could it be that I have very low input signal from the microphone because of missing L1? Bias generator ...
2
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2answers
85 views

Voltage reference vs voltage regulator

I need to bias some op amp inputs with a voltage. I’m in the 10-60 hz range. I need the bias voltage to be as low noise as possible, like -155 dbv . Would a voltage reference, voltage regulator, or ...
0
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1answer
66 views

Large ac input class AB biasing

I'm trying to bias the following circuit to power an 8 ohm speaker with an 8Vptp output. The following are the calculations I've done to get this current setup but the output is only good up to 1Vptp ...
3
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1answer
92 views

Constant-gm bias circuit

I am doing a study on Improvements in biasing and compensation of CMOS opamp. Do you guys know how to come up with the equation for RDS4C ?
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2answers
134 views

Why do we use one bias (VCC) for transistor amplifier circuits and 2 supplies for opamp circuits? [closed]

Opamps are said to have 2 supplies, so that the output can rail between these two points, then why do transistors have only one bias point.
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3answers
62 views

555 timer and biasing

Why is it that op-amps used as ICs, such as LM741 require a +Vcc and -Vcc for biasing whereas there is no -Vcc for a 555 timer? What determines the biasing for any IC?
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1answer
69 views

NPN transistor won't saturate when Vcc is greater than 7 volts

Am I missing something here? I have an NPN transistor (2N2222) with a 10K resistor from collector to Vcc. Also a 10K resistor from base to input signal. Emitter is grounded. The base input is ...
0
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1answer
59 views

How can a guy calculate the second collector current from this circuit?

This is an audio amp that we built for a project. I can easily find the first collector current from the first transistor by multiplying it with its Beta(200) and since the first transistor is beta ...
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0answers
39 views

Compensating transistor biasing

How to analyze the quiescent conditions of the circuit below assuming the tansistors are on an array such as CA3096? (Fig 5N.21 from Learning the Art of Electronics) Both emitters are at ground, so ...
2
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1answer
135 views

How to choose RF choke in the biasing circuit of varactor-tuned resonant circuit

I am new to circuit and has a very basic question about how to set biasing circuit of varactor. I need to use varactor to tune the resonance behavior of Split ring resonator (SRR) structure when ...
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1answer
406 views

Forward biasing of a BC547 transistor doesn't turn on LED

I have a setup as shown below: simulate this circuit – Schematic created using CircuitLab I am using the transistor as a sort of a switch. I am ensuring about 0.7 V (approx) is provided from ...
0
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1answer
176 views

Help with design a mic preamp with opamps for PGA and ADC

I want to sample an audio source using an electret microphone and analyze the spectrum of it with a uC. I'm interested in the 100Hz-2.5kHz range, so I calculate with these values when I tried to ...
3
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1answer
1k views

Biasing high frequency BJT cascode amplifier

So far, no one in the course has gotten both primary spec: 14.125 (with 1 V/V swing either way) nor 3dB-bandwidth of 500kHz to 20MHz using the 2N4427 (datasheet). Vcc = 9V I_CQ = 10mA-15mA I have ...
0
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1answer
176 views

How to bias MOSFET for finding S-Parameter simulation?

I wanted to use a BSIM4 model of NMOS in my circuit. I got the correct dc biasing point, certain VDS,VGS and IC. But I am having issues measuring S-parameter data for MOSFET amplifiers. I simulated ...
3
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2answers
349 views

How do coupling capacitors in transistor not affect biasing?

I understand the usefulness of the capacitors in an amplifier circuit but i dont understand why we use one at the input? and how does this not affect the biasing if it removes the dc voltage? Thanks.
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1answer
44 views

Confusion with understanding the fixed bias circuit

Below shows a bipolar transistor in fixed current bias configuration. A text says that this topology is independent of β: What I understand is, since Vcc, Vbe and Rb is constant the base current ...
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0answers
68 views

Does applying dc bias to a signal make it stronger?

I worked on a device that mimics a triode vacuum tube. But it doesn't use any vacuum, instead, it uses an electrolyte. I got several of them working, and I can make them switch, by making the "grid" ...
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4answers
505 views

why is the feedback or gate resistance RG necessary?

Here the large feedback resistance RG interposed between gate and drain of the NMOS (usually in the megohm range) forces the dc voltage at the gate to be equal to that at the drain (because IG = 0). ...
0
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1answer
40 views

Verify bias voltage with no load

I have a device that can be configured to maintain a specific bias voltage on the output. How should I verify if it actually generates that specific voltage? I do not think I could simply use a ...
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2answers
348 views

Biasing an IC CC-CE cascade amplifier

I have the following CC-CE (Common-Collector Common Emitter) cascade amplifier: I am trying to bias the amplifier by using LTSpice. Here is my schematic below: Apparently, from the displayed ...
0
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1answer
69 views

Bias Tee design for 150V AC and 150 DC at 40 - 50kHz

my question seems to concern a really easy device. But since I am new to this field of the magical electrons I am very eager to be careful and thankful for any help. My task is to power an ultrasonic ...
0
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2answers
338 views

Emitter resistance in transistor bias

I am having issues with the emitter resistance during biasing of the transistor. Can someone explain me what's the point of using this resistor? It is getting very not intuitive for me.
2
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3answers
94 views

How can I “filter out” a small offset current from a current source?

I have a current source that produces a 1 kHz 1 mA sinusoidal current. Unfortunately it also outputs a small DC offset current (microamps). The current source does have a small trim pot to zero out ...
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3answers
7k views

What is a self biasing of a transistor. Explain with a circuit of it

There was a question in my semester exam. "Define stability factor. Explain self-bias circuit with diagram and derive expression for stability factor." Now after searching a bit I found that when the ...
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0answers
514 views

Output Voltage Minimum Limit of LM358 as Error Amplifer

I am using one side of the LM358 as an error amplifier with a gain of 1, biased according to this MIT lesson for differential amplifiers. The results below show me tuning the reference signal to see ...
1
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1answer
278 views

How to Bais a tuned rf amplifier and compute I/O Impedances

Can anyone point me in the right direction on how to implemented the depicted tuned r.f amplifier? Since the load resistance at the collector is replaced by the LC tank how does one go about in ...
0
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0answers
186 views

When to bias diodes in double balanced ring mixer?

Do I need to bias up the didoes in a double balanced ring mixer? Some diodes have turn on voltage at 0.3V, and some turn on at 1.2V. If LO power is about 5dBm (~0.6V peak voltage), I would need extra ...
0
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3answers
312 views

How to bias a voltage for an ADC

I am part of a project that is implementing a power storage system. The storage device voltage must be monitored in order to direct power. The storage device voltage should remain between 12 and 36 V. ...
5
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2answers
5k views

BJT Voltage Divider Bias Circuit problem

Let's say we have the following circuit: The known values are: \$\beta=100\$, \$Vcc=2.5V\$, \$V_A=\infty\$ (meaning the Early effect is not taken into account), \$V_{BE}=0.7V\$, \$I_S=8\cdot10^{-16}A\...
0
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1answer
364 views

DC analysis of common-drain NMOS amplifier

The DC analysis is regarding the amplifier calculations, but that is not relevant to the topic. The equivalent DC circuit of the amplifier is: The known values are: \$Rg1=300k\Omega\$, \$Rg2=200k\...
1
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2answers
142 views

Pre-amplifier biased to one-half of power source

There is a schematic of an pre-amplifier that use one-half of voltage source output biasing (T1 emitter is one-half of V1). How the resistive network was calculated to allow one-half output Q-point? ...
1
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2answers
2k views

Difficulties in biasing MOSFET push-pull amplifier

Everything works perfectly well and following the expected in the simulations on MultiSim. This is what the test-version of my circuit project looks like: I made this version of the circuit to ...
2
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2answers
371 views

RF mixer theory and short circuits

Suppose I have the following RF mixer circuit- How does placing two AC voltages of differing magnitude and frequency directly in contact with one another not create a short circuit condition in a ...
1
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2answers
592 views

Wide Swing Cascode Current Mirror Biasing Difficulties

I'm working on designing a cascode current mirror, depicted below: Constraints: all Von needs to be above 200 mV, all Vds neds to be at least double Von, L is 0.35 um. Derived from the SPICE file, k'...