Questions tagged [bias]

A DC voltage or current in a circuit to set the operation point of an active or non-linear component.

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2answers
68 views

JFET Vgs Calculation Equation

Does anyone know the formula to calculate the Vgs of a JFET used as a variable resistor? Say, I have a Vds of 24v and I require a current of 20mA (just arbitrary values) I would need a 1.2k resistance,...
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5answers
1k views

Isolated audio without a transformer

I'm putting together a guitar pedal for splitting the signal to two different amps. One of the features I want to put in is a 'ground-lift'; isolating the signal to avoid ground loops between the two ...
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3answers
190 views

VBE Multiplier with Emitter Resistance Cancellation

Function of shown circuit is biasing of output power stage complementary audio amplifier. P1 allows precise adjustment of \$ V_{CE} \$ of VBE multiplier and \$C_B\$ improves its rail rejection. \$ r_e'...
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2answers
96 views

Several questions on video circuits

Part 1: Looking into several old good home computer video output circuits I see the similarity I can not fully understand. They use diodes or transistors as a bias for the final output section. See ...
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0answers
47 views

Applying a 1/3 bias to an LCD display spec'd at 1/2 still safe?

We're currently using an MSP430 with an integrated LCD controller that only has a 1/3 bias mode. The LCD display has a 2-mux configuration and the data sheet specifies "drive method: 1/2 duty, 1/2 ...
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1answer
54 views

Presence of Crossover Distortion in Class A Amplifier

This question is about theory facts of class A audio amplifier. It is known that class A amplifier is usually biased so that an amplifier's quiescent point is in the middle of the amplifying device's ...
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3answers
925 views

Why is the collector feedback bias popular in electret-mic preamp circuits?

I got some simple electret microphone modules and I've been experimenting with audio amplifiers. I googled to find some example circuits, and I found that most of them resemble the circuit above. I ...
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1answer
53 views

How to Model a Bias Tee in ADS

I'm modeling a Bias Tee in ADS and I wanted to ask how to add board parasitics into the model and what should the results of a good model look like in terms of the S-parameters. This is my first time ...
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0answers
43 views

How to bias an AC input composite video signal [duplicate]

This is a question about biasing 0V-referenced AC input signals to a positive single-ended signal. Even if the best solution for my question would be something else (and I'd like to hear about that, ...
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1answer
67 views

Cascode Amplifier Biasing Sequence

I'm trying to understand the proper biasing procedure of a cascode distributed amplifier part that requires three power supplies. A positive drain-source VDD, a negative gate-source VGG1, and a second,...
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1answer
50 views

Lower noise in biased op amp

I have a circuit similar to this. I’m trying to lower my noise under 60 Hz. Using pspice I keep finding that I need a very large resistor for R5, like 50 gigs but in practice this is not giving me the ...
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3answers
94 views

Audiable pops when switching DC biased audio signal

In my previous question, I have asked how to DC bias audio signal for a crosspoint audio switching matrix (Switch array (crosspoint) and DC biasing of audio signal). I am using the following circuit ...
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2answers
46 views

What bias voltage is applied to a PIN photodiode when connected only to multimeter

If I take just a PIN photodiode (e.g. BPW34 FAS ) and connect a multimeter to its terminals to measure current, for example: expose the photodiode to the sunlight and read current of ~1 mA on the ...
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2answers
53 views

Input Bias Compensation Resistor Calculation for an Integrator

I have been reading the following tech note from Analog Devices that discusses designing an op amp circuit to compensate for the input bias current: https://www.analog.com/media/en/training-seminars/...
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37 views

What would be the difference in the voltage transfer curves of this two circuits, assuming the op-amps are not ideal?

How does the resistor connecting the non-inverting terminal to ground affect the transfer curve?
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2answers
54 views

Single Stage Amplifier CMOS - Biasing Issues

So this is kind of vague question. I'm wondering what the approach to biasing MOSFETs in saturation is. For the following circuit, I really have no specifications - I'm just trying to play around ...
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1answer
205 views

Driving a butterfly package DFB laser

I want to drive a DFB laser in a type-2, 14-pin butterfly package. The manufacturer has provided limited information on how to bias the laser diode and could not get any information on the reference ...
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0answers
52 views

How to solve practical OPAMP with finite differential resistance and finite offset current while other parameters can be considered ideal?

simulate this circuit – Schematic created using CircuitLab Ip(bias)=200nA rd=differential resistance=5Mohm a=infinite What should be its output? I am confused if I should consider negative ...
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1answer
43 views

How does the spectral response of a photodiode change with bias voltage?

Look at this data sheet, in the second page we have a graph for the spectral response. Now, I have learned that photodiodes must be reverse-biased in order to get a decent signal from them, but then ...
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1answer
233 views

Inject 5V bias power (“fake” phantom power) for microphone (ModMic)

I've recently bought a ModMic4 for my PC, but the signal level is very low and have to amplify it quiet a lot digitally, which introduces ton of white noise and I have to use noise supression which ...
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3answers
64 views

Behaviour of Voltage on Base in a fixed BIAS Common Emitter Amplifier

I'm having some trouble understanding the behaviour of the basic common emitter fixed bias amplifier. I've been looking at this for awhile now and I'm starting to think there is a foundational ...
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2answers
204 views

In an AC coupled Op-Amp circuit where do input bias currents flow from?

If we have an AC coupled amplifier like the one below, i've read and been told it needs a DC path to ground to allow input bias currents to flow, though I just can't get my head around this, I bias is ...
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2answers
61 views

making a photodiode module

I am trying to do stimulated Raman scattering microscopy. In this experiment two pulsed laser beams are used . The wavelength of these two laser beams is tuned to match a specific Raman frequency of ...
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1answer
45 views

Basic questions on biasing

I have some trouble understanding a basic concept. Here is my question. This is from a document which can be found on the website, http://www.ti.com/lit/ug/tidu765/tidu765.pdf The text ...
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1answer
37 views

If positively biasing amplifier does minimum voltage on input pins apply?

I am using an amplifier to bias a signal for an ADC. The signal range is -1.25 to 1.25 volts. I have the 2.5V precision reference for the ADC through a voltage divider to the inverting input of the ...
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0answers
148 views

Choosing an inductor for a bias T

I'm creating a Bias-T circuit for a certain application. When choosing my inductor to block my AC-signals I know for example the proper inductance to choose etc. However, what I am having trouble with ...
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1answer
52 views

Why is the source voltage 1/4 of the supply voltage applied to the drain in a voltage-divider JFET circuit?

According to a Junction Field Effect Transistor (JFET) article in ElectronicsTutorial, the voltage across the source resistance is equal to 1/4 the supply voltage applied to the drain/gate for a class ...
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1answer
287 views

when a diode is forwards biased can current flow backwards through it?

when a diode is forwards biased can current flow backwards through it? this question comes from me trying to understand class AB amplifier biasing, so any additional comments about the diodes' use ...
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1answer
64 views

Bias resistor in opamp circuit

For the circuit below, what is the purpose of the 2 bias resistors. They are said to detect breaking, what does it mean.
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1answer
446 views

How to bias(voltage offset) unity gain buffer

First post so sorry for any bad formatting. I'm trying to figure out how to bias my signal going through a non-inverting op amp with a gain of 1. Because I want a gain one just 1, it would just be a ...
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1answer
51 views

how to adjust drain bias to keep power dissipation constant (HEMT)

I am reading a chapter in a thesis about using HEMT (high electron mobility transistor) as a cryogenic amplifier. The measurement scheme is to use the gate voltage fluctuation's influence on the drain ...
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2answers
83 views

Understanding of class-AB currents

I am trying to understand a simple class-AB output stage. The bias voltage for the transistors is made by using two diodes. The following picture show the circuits. The currents drawn are how, i ...
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2answers
118 views

Need help to increase schmitt trigger sensivity in a circuit

I need help on a circuit I've designed to detect hits on a piezo sensor on a drum. It uses an opamp with 2 channel, on goes to a schmitt trigger, the other to the ADC input on the XMEGA ...
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3answers
435 views

Gilbert cell biasing

I'm new here so I'm going to make is as simple as it can get.. How can I bias a Gilbert cell with bjt transistors like this one: What methods can I use to bias the transistors? Is there any example ...
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2answers
94 views

how can I get leakage current in tlp?

I got tlp test data and found that the current at vertical line means leakage current. But I don't understand the method how does the tlp-test measure the leakage current. I tried to search the ...
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1answer
38 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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1answer
361 views

Input bias current compensation

I am studying the Input Bias Current compensation technique by connecting the resistor to non inverting terminal of opamp. why the reistor of bias compensation should be parallel value of Rf & Ri ?...
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3answers
546 views

Some questions about the emitter resistor added to the fixed bias circuit

In many texts it is mentioned that the emitter resistor stabilizes the bias circuit. For example particularly for the below example: Which quantity is aimed to be stabilized initially? Vbe? And how ...
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2answers
92 views

Is the following equation wrong in this BJT DC bias analysis?

I came across a section of a tutorial regarding BJT DC analysis as follows: The first two equations for Ic and KVL for the BE loop seems correct. But I'm stuck at the last equation inside the box ...
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1answer
76 views

How does the voltage divider model a voltage source in this transistor bias circuit?

I encountered a text which says that the leakage current Ico (or called Icbo) adds up to the signal current hence causes thermal runaway because it causes temperature to increase and it also increases ...
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0answers
76 views

Amplifying DAC output with common-emitter configuration

In my current project setup I generate audio signals from my MCU's internal DAC. These audio signals are transferred to a speaker box with an internal amplifier via phone jack. To make the whole ...
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2answers
284 views

Why wouldn't my latching switch circuit turn off?

I built this latching switch circuit: https://www.edn.com/design/power-management/4427218/Latching-power-switch-uses-momentary-pushbutton When I connected it to my project (~140 LEDs) I found that I ...
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1answer
46 views

Bias T to level shift output from oscillator

I am using XOR gate HMC851LC3C to get an ultra-short pulse (200ps range). This logic gate requires inputs in the range of -2.5V to 0.5V. However, RF signals from my oscillator is sine wave -1V to 1V. ...
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1answer
162 views

Do we have a voltage drop across this ideal current source?

Additional info includes Vss=0V, Vdd=3V. Also assume saturation (since we have Vd=Vg) and λn=0. We also know the reference current but not the Resistor. I know Vgs and thus Vds but I am looking to ...
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1answer
116 views

Solving Unkonw R1 and R2 in classic descrete BJT bais arangment

im stuck solving the RB1 RB2 values is a classic discrete BJT circuit bias arrangement. Im sure its a simple thing that im just not seeing. Circuit values given are Ie=1.5mA V collector to emmiter =...
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1answer
159 views

Attenuator with strong bias

I am trying to come up with simplest solution to reduce 0~2.5V DAC output to 0.09V swing and shift it into -19.34~-19.25V range for controlling current limit of OPA548 op-amp within 0~100mA. There is ...
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1answer
280 views

Voltage divider bias (BJT) leads to a huge voltage drop across the collector resistor. Why?

I've already looked for similiar questions, but couldn't find any. Basically, I'm new in electronic circuits analysis and, after following my professor's lecture and looking on the internet I found ...
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1answer
130 views

Amplifier Causing Problems When Observed at DC

INTRO: Hello everyone! I am experimenting with audio amplifiers for a while now. I learned how to do an operational amplifier with discrete components and understand all its section and sub-circuits, ...
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1answer
109 views

What is the real problem with fixed point bias circuit?

In the circuit below, the texts mention the problem with this kind of biasing here is if the hfe(β) varies then the Ic will vary in linear reagion. (What varies what here also not clear, I thought all ...
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4answers
184 views

How do I reverse-bias a resistor?

We all know that a photo diode can be used as a light detector and as a light emitter (although the way that it's built will usually make it specialized to prioritize one application over the other); ...