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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3answers
334 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
73 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
96 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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194 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
164 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
356 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
222 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
57 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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177 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
102 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 ...
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2answers
262 views

Why is a common mode bias required for this differential amplifier? [closed]

TI makes the ADS1118 which is an ADC with a programmable gain amplifier (PGA). In one of their application examples (page 4), they indicate that small differential input voltages (1-2mV) must have a ...
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1answer
91 views

DC voltage in collector after active load

I am trying to analyse the DC Q bias point of the following circuits with a current source/mirror involved. I do not know how to calculate by hand the Q2 and Q5/Q4 collector voltages. All the currents ...
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1answer
296 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\...
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3answers
343 views

Single supply op amp to convert 0-5VDC to +/-2VDC (microcontroller to line level)

I am generating a 0-5 volt sine wave using an arduino with a DAC. I would like to level shift this signal (DC bias?) by -2.5 volts and have a gain of .8, so that I end up with a line level sine wave. ...
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2answers
137 views

Need help with instrumentation amp behaviour

I was wondering if someone could help me understand why this instrumentation amp isn't working the way I think it should. The amp is an INA155. My intention is that at if a voltage (positive or ...
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2answers
236 views

How Replica Feedback bias circuit rejects supply noise?

I attached the circuit diagram along with a short description of its working principle. However, it's not clear how the circuit rejects supply noise. It will be great if someone can brief about what ...
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2answers
528 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'...
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1answer
79 views

Balanced Class A Quiescent Current Regulator (OPS of Amplifier)

In my book there is a circuit like the one shown bellow. The author (G. Randy Slone) explains the operation and performance of it but there is still one thing that left me wondering. simulate this ...
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0answers
98 views

Common emmiter amplifier collector current selection when using a current source to achieve symmetrical output swing

I know how to bias a common emmiter configuration when using resistors, my main interest is biasing the transistor in a way that maximum symmetrical output swing is achieved, when using resistors, ...
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1answer
39 views

Unmatched connectors on condenser mic and wireless belt pack - make adapter?

So I want to buy a Shure Earmic (condenser) which has a mini XLR connector with 4 pins, one of them in the centre. And I want to connect it to an AKG PT40 body pack which has a three pin mini XLR ...
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4answers
811 views

adding dc bias to my signal

So I am having trouble understanding the following schematic. It is supposed to take an input through the capacitor C6 which is an AC sine wave and add a DC bias to it. However I do not understand how ...
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2answers
138 views

Why is this resistor connected in such way?

Why is the R2 resistor connected to bias instead of ground? As far as I know, only one of the op-amp's inputs has to be biased, so why such configuration? Also, how does this affect the gain? Edit #1:...
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2answers
116 views

Another solution for all MOS are in cutoff saturation region

Here is a two stage amplfier with a beta multiplier bias(lab3),the schematic of lab3 is in the second picture. I simulate them when VDC is 1.8v and 1.98v for tt-corner and ff corner in 25 degree ...
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2answers
397 views

MCP4921 audio: removing output DC Bias

I've seen a number of posts out there concerning adding/removing DC biases, and I can't seem to find one that has been directly applicable to my problem. Question: How do I remove the 1.5V DC step ...
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211 views

BJT Transistor Biasing Problem

If I have the circuit where I have Vcc = 30V and Vee = -30V. Transistor's beta equals 300. I want my Ic to be around 10mA and Vce = 25V, Vrc = 25V, Vre = 10V. I want to bias the base of transistor ...
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1answer
419 views

BJT one stage amplifier with current source

How I can correct my schematic to properly set the current source in the emitter of BJT common emitter stage? I can't understand how to properly bias the Q1 using R3/R4 voltage divider. How to find ...
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1answer
144 views

Differential Amplifier Input Line-Level Signaling

This is the circuit I'm referring to: This stage is often used as input stage of audio amplifier. I am wondering, how can the input signal be normally amplified since there is no DC bias across the ...
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1answer
121 views

Diode connection in reverse bias

Please help. In reverse bias we say the negative terminal of the battery attracts holes of the p-type hence depletion zone becomes bigger. Why don't electrons from the negative side of the battery ...
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3answers
379 views

Bjt amp with 2 voltage sources bias point

I'm trying to bias the bjt amp with two voltage sources and make the collector of bjt at 0.5V to maximize output swing but the simulation give me too much different result, why? The collector current ...
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1answer
388 views

AC current measurement with ATmega328

I am trying to reconstruct and measure AC current with a current transformer (ratio 1:2500) and an MCU (ATmega328p) like shown in this schematic, so the input voltage will be between 5V and 0V with ...
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1answer
116 views

What would happen to the DC bias voltage of the emitter if this capacitor is omitted?

I'm not quite sure what the question means. I need to explain what would happen if I removed the \$1.0 \mu F\$ blocking capacitor from this circuit. Howver, I'm not sure what the "DC bias voltage of ...
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1answer
423 views

How does the voltage difference develop when MOSFET is biased with Current Source?

I have a circuit in LTSPICE which is performing as desired but I could not understand the working of it. Basically I have an NMOS circuit shown below (fig a): Here are some values which I calculated ...
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2answers
3k views

Input coupling to Class AB amp with diode bias. One capacitor or two?

When AC coupling the input signal to a Class AB (Push-Pull / Complementary Pair) which is diode biased I see two different approaches: Signal connected between biasing diodes with single decoupling ...
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2answers
576 views

MOSFET H-Bridge Amplifier Unbalanced Gain

I have been designing a 100 watt, high frequency (20 - 40 kHz), bridged amplifier using MOSFETs. Although I have some systems and electronics background, the behavior of the MOSFETs is a bit beyond my ...
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1answer
93 views

Would AC voltage damage the capacitor if using a low voltage rating capacitor?

So I have a circuit below: C1 is 6.3V rating electrolytic cap. V1 is 6VDC V2 is 2VRMS The DC voltage across C1 cap is 6V and I have 0.3V margin. Since the AC voltage at both terminal of the cap is ...
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4answers
2k views

How to keep the bias current constant in class AB output stage?

I am working on a hobby project to build a small audio amplifier. Actually the idea behind the circuit is to build a 0.5W-1W audio amplifier that can be powered from a single 9V battery and have ...
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1answer
278 views

DC biasing arrangement in this audio phase shifter circuit

The circuit is composed of four phase shift opamp stages each with a JFET used as a variable resistor. Part of the circuit I do not understand is the DC biasing arrangement. I can see that it uses a 4....
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1answer
203 views

Clipping of a negative feedback amplifier

I need help solving the following exercise from my book. I am not very knowledgeable in analyzing biasing circuits but I have understood the following: \$R_1\$ and \$R_2\$ are feedback resistors. ...
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3answers
1k views

RS485 termination: AC + failsafe + parallel + bidirectional

Knowing that I need to refine my RS485 circuitry, I've been reading. I have a series of specific questions and I hope that you'll indulge me as I describe how I attempted to follow through an ...
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3answers
1k views

Opamp input voltage divider creates wrong voltage - what could be the cause?

I'm using above 1:2 differential opamp, when 72V applied to the 30:1 voltage divider, voltage across R1 is only 1.727V instead of 2.4V, opamp output is around 3.4V. Opamp is LMC6062IN/NOPB http://...
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1answer
717 views

FET Practical DC Analysis Problems

I just finished with theory understanding of FET transistor principles, etc. Right after that I tried to make simple circuit Common-Source with FET and MOSFET the problems occurred one by another. I ...
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2answers
664 views

Strange Voltage Levels in a Multi-slave Full-duplex rs485 bus

I am working on a project using rs485 bus for communication. Here are design parameters: Bus can include 1 master and 30 slaves Configuration is full duplex using 4 wires. All slaves attached to <...
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2answers
477 views

Increase low-frequency gain of a cascode amplifier

I've been designing a noise generator (for fun) with the goal of getting a smooth frequency response between 10Hz and 10MHz. Since I don't have any "fancy" op-amps, I decided to go with a discrete ...
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2answers
317 views

Need help DC biasing an AC source

I am trying to simulate this circuit I saw here: However, when I simulate it, the "mid-point" does not behave like the blue line in the above picture. You can check the simulation here: Is the ...
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1answer
413 views

Biasing analog MEMS microphone [closed]

I am using a analog type MEMS microphone.(SMA120). Interface chip PCM2912 provi SMA100 data sheet PCM2912a data sheet PCM2912 product page not for new designs Could you kindly suggest me a proper ...
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3answers
616 views

Biasing of a circuit with two transistors BJT

I need to calculate the bias values. So far I have only written these equations, but something is missing. (\$\beta=200\$ for both transistors and \$V_{BE\,on}=0,6\,V\$) Capacitors=open circuits \$\...
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2answers
510 views

Designing an SMPS circuit on eagle (finding the right transformer and parts) 230VAC to 5VDC

I'm very new to the world of electrical design. I'm trying to create a SMPS circuit on eagle and am struggling to find the right transformer. I'm currently following this circuit (page 7): https://www....
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0answers
692 views

Solid State Output Tube Driver for a SE guitar amp

I'm learning as I go once again. Consider this output stage segment from a guitar amplifier I physically built: The LND150 is an "depletion mode" MOSFET, whereas the IRF820 is a normal "enhacement ...