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Questions tagged [amplifier]

An amplifier can be used to adapt the range of the signal to a requirement, to make it more robust for transmission, or to satisfy interface requirement (like input/output impedance)

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24
votes
2answers
19k views

BJT in Reverse Active Mode of Operation

What will happen if for a BJT transistor, it's emitter terminal is treated as collector and collector as emitter in a common emitter amplifier circuit?
4
votes
3answers
710 views

Differential and Multistage Amplifiers(BJT)

I want to determine the currents in each of the branches. I could analyse the current mirror portion and the differential amplifier portion, but facing problem thereafter. I could find the ...
2
votes
1answer
774 views

selecting a TIA - and using it for 60dB dynamic range

before entering in to problem: my application is a laser pulse detection, in this process when a laser pulse falls on photo diode it generates current, for which i need a Trans Impedance Amplifier (...
1
vote
2answers
365 views

Cant understand an ab amplifier diagram

I been trying to figure out this diagram, and Can't understand what happens from the beginning of the input , how the voltage changes in a way that "shuts off" one transistor. Also cant understand the ...
1
vote
3answers
1k views

BJT Input AC Signal Amplitude

This question is referring to npn BJT CE: If we look at base voltage vs. collector current plot we can see that at approximately 0.7V on base to emitter junction, the BJT starts rapidly conducting. ...
3
votes
3answers
4k views

How does this Push-Pull amplifier work?

I'm reading about op-amp circuits that use negative feedback from this article (question no.19). What confuses me is that the negative feedback for the Op-amp (which is being used to reduce ...
12
votes
3answers
14k views

How do I get +5v for loud noise, 0v for silence from Electret Microphone (or other components)?

I have been asking a few questions here to get to a proper one, the initial questions I asked are linked to at the end. I used Fritzing to make up some schematics of my initial thoughts, but at the ...
8
votes
2answers
2k views

Logic level converter using Transistors

I am trying to make a logic level converter using transistor BC547. This is to convert Voltage level of Rpi Gpio from 3.3 to 5V. I have wired the circuit according to this diagram: I have done this ...
1
vote
3answers
669 views

BJT 2 stage Amp. Output problem

So I built the following circuit to amplify the output from my microphone. I am testing it using a 1KHz sinewave of 10mV peak value. The Mic is biased using a 10k resistor. The signal is input into a ...
17
votes
6answers
58k views

Why is feedback required in op-amp circuits?

I understand that, in order for an op-amp to function correctly, a DC feedback loop from the output to either the inverting or the non-inverting input (depending on the external circuitry) is required....
34
votes
2answers
3k views

What's the difference between field-effect transistors (FETs) marketed as switches vs. amplifiers?

For instance, the J108 JFET is listed as "N-Channel Switch", and the datasheet mentions the RDS on resistance, while the J201 JFET is listed as "N-Channel General Purpose Amplifier" (and the on-...
5
votes
4answers
8k views

What is the bypass capacitor at the emitter of a common-emitter amplifier for?

Why do we have the by pass capacitor parallel to R(E) in this amplifier circuit? They say it is to bypasses the RE resistor for AC signals but then why is it required to by pass the R(E) They say ...
3
votes
3answers
1k views

Difficulty with Common Emitter Amplifier

I'm trying to take the input from a microphone and use it to power an LED, so that it's off at ambient sound, and (the peak brightness) gets brighter with noise level. It's okay if it flickers, I'm ...
1
vote
3answers
1k views

BJT Amplifier with Emitter Bypass Capacitor Design [closed]

I am trying to design a BJT amplifier. The circuit is shown below with its parameters. beta=180 RL=20kΩ VA=0 (early effect can be ignored) VCC=15V There are three constraints listed below: Swing ...
13
votes
3answers
45k views

Scale 30-50 mV signal to 0-5 V range

I have a CO2 sensor that output signal values 30-50 mV. I need to translate these voltages to 0-5 V for my microcontroller with the highest resolution. I understand that I can amplify the ...
6
votes
1answer
529 views

Amplifier capacitors

Why is that when I use electrolytic capacitors (the cylindrical ones) and measure the end with respect to ground, there is some DC voltage appearing (where in fact it should be 0 volts since capacitor ...
4
votes
3answers
41k views

Role of capacitors in amplifier

What is the significance of a coupling capacitor in a common-emitter amplifier? What would happen if it is removed? What will be the effect on AC amplifier gain on removing it?
3
votes
4answers
3k views

Basic Frequency Control Circuit

How does R4 prevent the output voltage drifting towards one of the supply rails to the op amp? I understand that R4 has to have a high resistance but I do not know why? Here is the schematic which is ...
0
votes
2answers
689 views

BJT common-base output resistance derivation

In Sedra/Smith the following image may be founded that is used for output resistance equation derivation of common-base BJT amplifier. The question is why the gm*v and v/re currents are directed up? ...
4
votes
3answers
2k views

BJT Bias Design and Operating

I'm to the task to design a BJT Common-Emitter Amplifier with resistance at the emitter as in the figure, and for that I need to: get the values for \$R_{1}\$, \$R_{2}\$, \$R_{C}\$ and \$R_{E}\$ ...
16
votes
5answers
60k views

Simple Audio amplifier Using Transistors

I would like to build a simple audio amplifier using transistors. I know there are IC designs specifically for the task. But i want to use transistors so i can learn how to use them for amplification. ...
9
votes
4answers
12k views

Can I use a PNP Transistor with an Electret Microphone to get an non-inverting output for my Arduino?

I'm looking to simply read the generic sound level from an Electret Microphone. I've seen a number of schematics with NPN transistors, that will provide an inverted output (~5V when quiet, ~0V when ...
7
votes
1answer
1k views

How to measure battery voltage

I am building a battery powered device. Almost all of my logic is running at 3.3v, although I do have a 5v supply for a few hobby servos. I want to measure the battery voltage, but I can't do so ...
10
votes
3answers
19k views

Input impedance of inverting amplifier clarification

Take a standard inverting amplifier: I'm unclear on what the input impedance is. At first I thought it was the equivalent resistance from the inverting input to the ground, which would be Rin || Rf, ...
3
votes
2answers
567 views

How does a Miller cap physically create a pole in circuits?

If we consider a single NMOS transistor (with its source terminal grounded) and a Miller cap (C) between its input (gate) and output (drain) nodes, circuit theory says that this Miller cap will be ...
1
vote
2answers
917 views

Common Emitter Amplifier Problem (Incredibly lower Gain than input, and Distorted)

I'm trying to create a common emitter amplifier to power a medium sized 8 ohm speaker as a learning experience using one NPN transistor specifically the PN2222A. Here's the design schematic in ...
8
votes
4answers
4k views

Amplifying a PWM signal with an op amp. Is the slew rate a problem?

I need to amplify a PWM signal from 5V to 24V in order to drive a mosfet that in turn drives a small DC motor. The input signal has a frequency of 500Hz and comes from Arduino uno (pin 9). For ...
6
votes
7answers
929 views

RC Lowpass Filter between Amplifier and ADC input

I have sensors (pyranometers that consist of thermopiles and measure sun irradiation) that ouput a low voltage signal so I need to amplify them using an instrumentation amplifier. I have chosen the ...
3
votes
3answers
621 views

eliminating those unwanted op amp[TIA] outputs

my problem statement: i wanted to digitalize 10ns pulses from a photodiode which are in the range of current 100uA to 1mA (these were earlier much larger in range, dealt here, soon I have ...
6
votes
3answers
483 views

Highly Distorted Output of Class B Power Amplifier

This is the circuit I made: simulate this circuit – Schematic created using CircuitLab This simple circuit incorporates differential stage - VA (Voltage-amplification) stage - OPS (Output ...
5
votes
1answer
3k views

use of diodes and resistors in a push-pull amplifier

I am a beginner in electronics facing a bit more difficult problem. what might be the function of the two resistors(R4,R5) and diodes(D1,D2)? in the circuit below?
4
votes
2answers
1k views

Confusion between Class B and Class AB Amplifier

I am reading about output stages of an amplifier and classes of amplifier. The following circuit is named as "Class B" amplifier. From my understanding, the above circuit should be a class AB ...
3
votes
1answer
812 views

Would an RF amplifier be required for an indoors antenna connected via coaxial cable to an outdoor directional antenna (900/1800 MHz)

Sorry, couldn't make the question title any shorter without losing meaning. So, I'm looking to build an outdoors yagi antenna that's connected to another indoors antenna via coaxial cable. The ...
1
vote
2answers
1k views

What is the benefit of using carrier frequency for an amplifier?

I provide the link here: http://books.google.dk/books?id=wnPNkbJUBxkC&pg=PA153&lpg=PA153&dq=carrier+frequency+of+an+amplifier&source=bl&ots=mtT6SOFuqJ&sig=...
0
votes
3answers
448 views

Common emitter with low voltage input

I have to do a project involving a common emitter amplifier. The only given data is: the amplitude of the input signal is 100u, and offset voltage is 0. I need that signal to be amplified. But my ...
29
votes
6answers
12k views

Noise reduction strategies in electrophysiology

When recording electrical signals from cells (in a dish or inside a living human or animal body), one major problem is to increase the signal to noise ratio. These signals are usually in the 10uV ...
26
votes
10answers
17k views

LM394 is obsolete. What is the new standard log amp circuit?

The traditional logarithmic amplifier circuit is described in National Appnote 311: This circuit uses the difference of two transistor currents to generate the log of the input over a pretty wide ...
12
votes
4answers
10k views

Effect of bootstrapping in amplifier circuit

I am trying to understand this "bootstrap bias" amplifier circuit. The picture below is adapted from the book "Transistor Techniques" by G. J. Ritchie: This circuit is a variation of the "voltage ...
11
votes
3answers
5k views

Choose the better values (in terms of range) for resistors in this non-inverting op-amp circuit

These days I'm looking at operational amplifiers; from what I've seen, implementing them in a circuit is quite simple, at least when they are connected as "non-inverting". Determining the gain/...
12
votes
1answer
3k views

Fully understanding LM386 datasheet minimum parts example

I'd like to fully understand the circuit marked as "Minimum Parts" at page 5 in LM386's datasheet: Is there any reason for 10k resistance at the input potentiometer or is it just an arbitrary value? ...
6
votes
2answers
11k views

Why is my audio amp picking up AM and FM radio stations?

I built an audio amp out of the LM386 on a previous question. I when I have nothing connected, I picked up FM radio stations, as well as AM Very loud and clear. Why is this happening? Why AM and FM? ...
3
votes
2answers
7k views

Zener Noise Generator - NPN BJT Amplifier Analysis

I'm interested in creating a low voltage white noise generator by means of a zener diode, as detailed here: Zener & BJT Noise Generator. Specifically, I want to use the circuit here, in order to ...
14
votes
2answers
38k views

What wattage should a headphone amp be?

I was at a local surplus store today and I got two LM386N ICs. I thought I could make a really simple headphone amp out of these. But I have no idea what the wattage of a normal headphone amp is. ...
8
votes
4answers
3k views

Controlling a current with another - home-made alternatives to the transistor?

I have a very basic understanding of how a BJT or a FET works, but I think I got the idea. They are awesome in all regards, except one: you can't make one at home without hot ovens and scary chemicals....
8
votes
4answers
8k views

How do diodes and capacitors reduce Crossover distortion?

I found this diagram about Class AB Amplifiers and the reduction of crossover distortion: http://www.electronics-tutorials.ws/amplifier/amp_7.html This pre-biasing voltage either for a ...
8
votes
4answers
664 views

BJT Puzzler: Common Emitter or Emitter Follower?

A few high-reputation members have disagreed on this in the context of other questions, so I thought I'd post it as a separate question. Question: Is the NPN BJT in this circuit configured as common ...
7
votes
1answer
2k views

Charging two lead-acid batteries connected in series, separately (with two solar panels)

I have two lead-acid batteries connected in series to produce 24V. They are powering an audio amplifier. I'd like to be able to charge them while they are powering the amplifier, with solar panels. ...
4
votes
2answers
2k views

Adding negative feedback to a common-emitter transistor amplifier

I am trying to learn how to implement negative feedback to a common-emitter configuration.The goal is to reduce distortion by sacrificing some of the gain. simulate this circuit – Schematic ...
-2
votes
2answers
295 views

Amplifying 10-30mV into at least 5V

My thesis title is "Powerbank with sound to eletrical energy converter" meaning I'll be using sound to charge the powerbank, and I decide to used dynamic microphone instead of condenser microphone ...
8
votes
3answers
2k views

Function of Specific Capacitor in Audio Amplifier's Negative Feedback

The audio amplifier that I am referring to here consists of three stages. Among others, the amplifier also includes negative feedback (NFB) that is made of two passive resistors. From the base of TR3 ...