Questions tagged [biasing]
93
questions
1
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7answers
619 views
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
1
vote
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}\$ ...
0
votes
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
votes
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
votes
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
vote
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?
1
vote
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
votes
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
votes
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
votes
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
vote
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
votes
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
votes
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
votes
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
votes
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 ?
0
votes
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.
0
votes
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?
0
votes
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
votes
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 ...
0
votes
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
votes
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 ...
0
votes
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
votes
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
votes
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
votes
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
votes
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.
0
votes
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 ...
0
votes
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" ...
0
votes
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
votes
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 ...
-1
votes
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
votes
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
votes
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
votes
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 ...
-3
votes
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 ...
1
vote
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
vote
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
votes
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
votes
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
votes
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
votes
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
vote
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
vote
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
votes
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
vote
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'...
