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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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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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36 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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46 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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151 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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45 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
40 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
69 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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53 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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109 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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38 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
43 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
32 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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69 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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47 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
221 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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61 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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184 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
49 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
54 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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83 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
311 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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79 views

Trouble with biased measurement for Oxygen Sensor EC410

I need to achieve a -600mV bias between Vsense and Vref for a potentiostat circuit. I'm trying to replicate the design for an Oxygen Sensor (EC410) by following the above image from the application ...
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2answers
82 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
36 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
289 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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387 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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85 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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69 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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38 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
244 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
43 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
139 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
93 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
135 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
233 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
107 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
98 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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170 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); ...
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274 views

Does Vbe remain constant when Vb changes but changes when Ve changes for this BJT biasing circuit?

I was reading about thermal runaway caused by Icbo in a BJT, and seems I understand how the temperature increases Icbo then in turn Ic and Ie. But I also read that the biasing circuit's emitter ...
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0answers
70 views

Transfer function of loop-back bias circuit for RF amplifier

I am trying to implement a current mirror as part of a bias circuit for a RF amplifier. I want to do a transfer function of the bias circuit since it creates a loop from the amplifier fet drain to ...
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1answer
51 views

What track does this bias current loop through?

Please see the edit. A source is coupled to a diff-amplifier circuit as sown below: The 10k R1 provides a path for base currents to return. But Im confused about the loop taken by ib2. For ib1 I ...
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1answer
93 views

How do non-flowing common mode or bias currents cause common mode range to exceed/float?

Below is a very simplistic view of differential ended inputs of a data-acquisition channel's inAmp which measures a floating battery voltage V. To make concepts and explanations simpler I use two ...
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172 views

Clamp-biasing at JFET Gate in RF Circuits

Reading the book Communications Circuits by Clarke and Hess, I came upon a chapter entitled "Clamp-biased Square Law Device" (Chapter 4 - 4.9). It took me a while to realize that they were ...
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1answer
122 views

MOS Cascode Bias Quesiton

I'm confused about how this circuit operates. Here's what I know. Vbias sets transistor Q2 in saturation. The input small-signal vi is applied at the gate of Q1 along with an appropriate DC voltage ...
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2answers
298 views

Understanding Minimum Output Voltage of Cascode Current Mirror

I guess that I have some serious trouble understanding how to get the saturation equation for the cascode current mirror right which is known from all the textbooks as $$ V_{out} = 2 V_{DS, sat} + V_{...
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1answer
178 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 ...
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1answer
32 views

How to connect two (or more) BJTs (collector of Q1 to base of Q2 for instance) and still make their bias voltages independent?

The question is in the title. I'm learning about how to use BJTs and was wondering how I could connect them in blocks the way bias voltages (thus operation modes) are not being dependant. Thank you!
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1answer
55 views

Input biasing and coupling calculations

I have a low frequency input signal 3-80 Hz that I am feeding into an inverting op-amp input. I am slightly confused as to what values I should choose for the following components - R3, C2, R4: The ...
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164 views

A good and valid example of Common Collector BJT

I am analyzing a common collector BJT as an amplifier using LTSpice. I have made the following circuit and I am not getting the exact characteristics which I should have got. Is there something wrong ...
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1answer
86 views

Why Use a Biased Resistor?

As a school project I was wiring up an IR LED in series with a biasing resist. I was using a breadboard and a vex cortex controller. I understand that a resistor is important because it prevents the ...