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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Amplifier Biasing [duplicate]

So I have amplifier circuit that is biased using a sine wave and a DC offset on the NPN and PNP see this question. Wouldn't biasing the circuit at 1v short out the circuit as VBE~07V? Here is a copy ...
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770 views

Bias DC signal from op amp

I've built a DC signal mixer that doesn't quite work as expected. The supply voltage is 9V, virtual ground at 4.5V and the mixer uses a TL074 quad op amp. While the input voltage is 0-9V, the output ...
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3answers
683 views

Small Signal RF Amplifer Limitations

Question: I am designing the following common emitter amplifier. This is designed with a BC547B transistor. My design is as follows: Vcc = 15V, IC = 30ma, VRe = 2.5 V, VRc = 5V, VCE = 7.5V. HfE = ...
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1answer
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Transistor biasing [closed]

I have learnt loads about biasing a transistor, but I never managed to understand them. They talk about DC load line, Class A, B, C and various types of biasing. What are they all about and where can ...
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1answer
4k views

What is the purpose of a resistor to self bias a MOSFET?

If there is no voltage drop across \$R_G\$ as I have been taught. What is the purpose of it?
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How to amplify electret microphone to range from 0-5V with bias of 2.5V?

I'm new to op amps and have tried many circuits but don't get the results I expect. I know I must do some math but I get so confused. I thought my question is really simple but it turns out it's not. ...
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3answers
2k views

Best way to go about biasing a Class B audio amplifier?

I am trying to bias the class be audio amplifier in the provided pdf. None of the resistor values are correct so the bjts are unbiased. What is the best way to go about starting to bias this? Circuit:...
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1answer
30k views

Q-Point of a circuit

In a BJT or MOSFET circuit we have this curve: What is that q-point? From my research I have the following information: The operating point of a device, also known as bias point or quiescent point ...
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3answers
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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}\$ ...
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1answer
992 views

Is Rg, calculated in the linked PDF calculating the pulldowm/pullup resistor for a MOSFET gate?

I stumbled upon the following paper while looking for ways to calculate a specific value for the pullup/pulldown resistor for the gate of a MOSFET. I see several calculations for Rg. Is that the ...
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1answer
1k views

How does the addition of a bias-t circuit affect the impedance of a transmission line?

I've got a GPS circuit where the antenna is connected directly to the GPS receiver via a coplanar waveguide designed for an impedance of 50ohms. Unfortunately, I neglected to add the bias-t circuit ...
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1answer
390 views

What EMC considerations need to be made with RF bias-t with 3-4A of current consumption?

After getting a great answer on how to couple a signal on to a DC line, I wonder what EMC considerations that has to be done with using a bias-T circuit used for communications with a ~130kHz QPSK ...
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2answers
3k views

Removing DC wander in the offset of a DC-biased audio signal

I'm trying to read an audio signal from an Android phone as a serial input to an MSP430G2553, adapting this design to use the MSP430's onboard comparator module instead of an LM324. The Android code ...
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1answer
1k views

Why amplifiers (RC coupled) are based on voltage divider bias?

What actually determines the type of bias to be used for different practical applications. Also I do not get the point of using capacitors (coupling) for emitter current and high input resistance. If ...
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1answer
2k views

Bias tee with very small low cut-off frequency

I need to measure the noise spectrum of a diode under certain bias. The noise frequency I am interested is in the range of several Hz to tens or hundreds of kHz. I am thinking of using a bias tee ...
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1answer
849 views

Bias analysis in a dual BJT circuit with feedback

I am building an Wooly Mammoth audio circuit, and I am really interested in finding how and why it works. You can check out and simulate the whole thing here. I must say I haven't been able to get ...
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2answers
309 views

Do Fixed Bias BJT 's have a cut in voltage?

I am doing a DC analysis of a Fixed bias BJT and am trying to calculate its collector current. So far I have these following values. I am using a MMUN2211LT1 bias resistor transistor network. My ...
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5answers
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Pull-up resistor over a microphone

What is the reason of that 1 kilo ohm connected to the microphone? Why always too high resistors are used? I couldn't find any explanation. How do we calculate these values?
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1answer
4k views

Is there any way to feed a signal (line-in) into a mobile phone?

My first post here, so please point out if I say anything silly. I'm working on an audio application for mobile phones. At this point in time I'm trying to measure audio latency of a mobile device by ...
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2answers
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Driving hard drive voice coil actuator with PWM

I have been trying to control a voice coil actuator with PWM input, but i have the following problems and would like you to correct or point me in new directions. I have an arduino which outputs PWM ...
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1answer
53k views

What's input bias current in opamps?

Is it the current you have to drive in the input to get a specific, defined voltage at the output? And don't the currents cancel each other when applied to both inputs?
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DC biasing audio signal

I have seen a few different ways of adding DC bias to an audio signal. I have simulated them and they all give me similar results, but I cant Figure out is why choose A over B or C. My audio source ...
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1answer
4k views

Simple Biasing Circuit

I'd like to formally understand this simple biasing circuit: Let V+ be the supply voltage, Vi be the input voltage at the seemingly unconnected terminal of the capacitor, and let Vo be the output ...
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1answer
2k views

Transistor with emitter resistor calculation

I can't seem to get over this but this seems to be the basics in electronics. I have an NPN darlington transistor TIP122 and have built to simple test circuit around it with Rb = 150 ohm, Rc = 80 ohm ...
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6answers
29k views

What is the purpose of a bias resistor?

Could someone explain what "bias" is. And why do some devices need an external bias resistor?