# Questions tagged [biasing]

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### HV Rectifier output for APD biasing

I am trying to convert low 5V or 12V to -200V using this device. Which converts it using transformer and rectifier at the output: Can I just attach HV OUT to bias APD detectors? Or is there any ...
• 11
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### Can I bias a depletion mode FET with a diode?

I'm trying to work out how to bias a dual gate MOSFET that I'm working with. Its behavior is halfway between depletion and enhancement modes. That is, its ideal VG range is about -1.5V up to about 0....
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### How does class AB amplifier biasing work exactly? [duplicate]

Can somebody please explain in both cases the biasing method? I don't understand the following points: It's OK that we need ~0.7V for PNP and NPN base-emitter voltage, that's why a diode is used for ...
• 11
100 views

### What's the emitter voltage of a 2N2222 transistor with grounded base and a sine wave at the collector?

Consider this circuit with a sinusoidal source connected to the collector and a pulse toggling between 0 and 5 connected to the base of a 2N2222 transistor. What I imagined the output being was when ...
• 161
181 views

### Class AB BJT biasing, diodes

Every time I see such circuits, it is assumed that the voltage drop across the diodes is exactly equal to Vj * 2. But this is simply not true. The voltage between the bases of transistors is highly ...
67 views

### Simple push-pull BJT biasing

Explain me please, how biasing exactly works here? From my view, on positive half of signal, we need about 0,7V + signal voltage (let's say signal is 1V) on NPN base, relative to its emitter=relative ...
76 views

### What is the function of emitter biasing of a transistor?

I have been reading about transistor biasing to counteract inaccuracies in transistor manufacture, add stability etc. One circuit I can't see the benefit in, which is diagrammed in the datasheet for ...
• 485
154 views

### Why is the depletion layer near the emitter region narrower than the collector region?

While studying Grob's Basic Electronics chapter 28 I came across this statement, Notice in Fig. 28–2 that the EB depletion layer is narrower than the CB depletion layer. The reason for the different ...
• 111
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### Analysis of power amplifier bias circuit: does it need to be thermally bonded?

I'm in the process of building a medium power amplifier for the 20m band (14MHz) and I'm experimenting with bias circuits. The amplifier is a classic BJT push-pull arrangement with a transformer ...
• 1,530
201 views

### How does gate-source voltage forward bias the source-substrate junction of MOSFET?

In forward bias, the p-type is connected with the positive terminal and the n-type is connected with the negative terminal. The junction that I'm observing is the source-substrate junction. The source ...
• 133
43 views

### NPN BJT Operation - What does it mean for the Collector - Base junction to be reversed biased?

According to this screen grab the Collector Base junction must be "reversed biased". I seem to be confused about the meaning of that. I thought that the Collector needed to be at a higher ...
• 87
1 vote
54 views

### CMOS Transmission Gate Body Bias in 74HC4052

Page 2 of the 74HC4052 data sheet shows a diagram of a transmission gate. I'm curious about the way the body of the NMOS transistors is biased. It looks like when the t-gate is off, the body is ...
• 111
1k views

### Why is the bias input current of an op amp a constant value?

I read this text on op amp input bias current. It says: The input pins are the base pins of the transistor (or gate pins in the case of FET inputs). In order for the input transistor to operate, the ...
• 3,027
1 vote
99 views

### Node voltage increases in voltage divider

I am planning to use a voltage divider in order to measure the capacity of a group of lithium batteries; in order to minimize power consumption, I biased a common-emitter switch (Q1) with the ...
• 557
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### How do I bias two OTAs without dividing the current?

I'm trying to achieve automatic gain control in an audio circuit, which requires me to use both diode pins of each amplifier available on the LM13700 chip. The diode pins accept a current (Idiode), ...
1 vote
140 views

### Common Source MOSFET Amplifier Biasing

While reviewing simple transistor amplifier biasing techniques I came across this paragraph in Microelectronic Circuits by Sedra & Smith. Here too we show the $i_D–v_{GS}$ characteristics for ...
• 13
141 views

### Why doesn't this non-inverting amplifier work with a biased signal in a real circuit?

I have a signal with amplitude of 200 mV biased to 4.5 V. I would like to amplify that signal (AC only, no DC gain) after biasing with a single supply op amp. I have tried a non-inverting op amp ...
• 91
58 views

### I have a carvin v3m 50watt tube amp head, red plating/bias help

The amp has 4 el84 tubes and 4 12ax7 pre amp tubes, the amp lost about half of its volume and the power tubes are red plating, is there any thing other than the tubes that I should be looking out for ...
1 vote
62 views

### Trouble analyzing biasing circuit

I'm having trouble analyzing this biasing circuit. It's supposed to shift Vin up by 1.4 V, and everything works when I simulate it, but I can't get anything out of the manual analysis. I know that ...
• 13
223 views

### How does a Zener diode and NPN BJT control circuit provide current limit or thermal shutdown via an NPN Darlington pass transistor?

Background Application: 1995 Ford Ranger Manual Control Blend Door Actuator This 1 page pdf guide shows the block level function of a manual blend door actuator (my component is from a Ford Ranger.) ...
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### Forward bias or reverse bias

What do we take, the flow direction of electronic current or conventional current through a diode if forward bias?
73 views

### Non-Inverting OpAmp Bias not acting as expected- UPDATE

I have been experimenting with an opamp as a noninverting amplifier for a Piezoelectric vibration sensor 0-1Khz expected. I am only interested in the positive portion of the signal as an average hence ...
72 views

### Need a design for simple switching circuit

I am trying to build a simple switching circuit using a transistor. I have a 6V source that I need to switch using a 2.7v "signal". So if signal output is at 2.7v, I need transistor to be ...
63 views

### BJTs dangerously getting hotter as drawn current accumulating

I already ask a few questions on this project (so i won't explain everything again as it would be too long). I basically have a high power opamp (OPA462) to which i feed a signal (but i offset it ...
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56 views

### Where should I connect the V_REF1 & V_REF2 if I want to implement this two stage operational amplifier to a bandgap reference?

This is just a very elementary question for you. But for me it is new. I have found this subthreshold op-amp which is a work by Engineers, Sumukh Nitundil, Nihal Singh, R. Balaji, Pankaj Arora. I want ...
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163 views

### How are the PNP transistors biased in this microphone circuit?

If I am not wrong, the biasing voltage to turn on an NPN transistor is emitter voltage + 0.7 volts. Similarly, the PNP biasing voltage is emitter voltage - 0.7 volts. Can someone explain how the two ...
64 views

### opamp with single power supply

I'm trying to build a 'panner' to mix two audio signals, basically a dry/wet potentiometer for an audio effect. It works as intended when I use a dual power supply like this: But stops working when I ...
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61 views

### What are the qualities that you look for in a 2nd stage LNA?

We are building a multi-stage LNA for a TR module we are building in the 144MHz and 440MHz range. The 1st stage LNA has to be the most sensitive---but what is important to consider when choosing a 2nd ...
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### How would you filter the DC input suitable for use to bias/power an LNA?

We are building a transmit/receive module for the 144MHz and 440MHz bands. As I understand, a good LNA can provide poor performance if the environment or the bias voltage is too noisy. What are the ...
• 798
1 vote
301 views

### Why we use Dual supply Emitter Bias in Transistor

As i am studying about DC Biasing of transistor, i am just able to fully understand only Base Bias after that i am stuck at Emitter Bias which is also called Dual Supply Emitter bias where we apply ...
96 views

### Darlington biasing design error in a commercial frequency counter oven control circuit?

I am repairing a commercial frequency counter (brand to remain anonymous) that had the crystal oven visibly overheat. There is a small PCB in the oven that holds the crystals, the oscillator circuit, ...
75 views

### Common base bias reduces input impedance

When biasing the common base as shown I was expecting the input impedance to be (1/gm1 + R3/Beta)//(R1//Rpi2). So we with Beta of 100, and biasing current of 250 uA I was expecting the impedance to be ...
73 views

### Schematic modification

I am trying to design a PCB for the biasing circuit. I found this application note from integratech. As you can see in the application note, it has input detection circuit and SPST circuitry. I need ...
90 views

### Which voltage is lower, 0V or -1V for connecting a MOSFET's source terminal?

In an NMOS transistor the source should always be connected to the lowest voltage. Does this mean that if the source was originally grounded, but then the drain was connected to -1V that the source ...
112 views

### Biasing an inverting Op-Amp using a voltage regulator

When biasing an inverting op-amp input using a voltage regulator (say, L7805), at the non-inverting pin, can we use the same regulator to power other ICs or should we only use it on the op-amp? Also, ...
856 views

### Low-voltage cascode current mirror biasing circuit

On the left is a low voltage cascode current mirror and on the right is a circuit whose left branch generates $V_b$ for the mirror. Razavi (Design of Analog CMOS Integrated Circuits 2nd edition, ...
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### Linear increase of collector current in CE mode of a BJT

Why is there first, a linear increase in the collector current in the output characteristics of an NPN BJT in CE configuration if we increase the Vce(collector-emitter) and then the current remains ...
• 137
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### Why can we bias mosfet with current source

I know that we can get desired DC current by supplying certain VGS asccording to the equation I=(1/2)*K(VGS-VT)^2. But the scheme shown in the picture does it in a reversed way. It is establishing a ...
• 151
258 views

### AC load line of a BJT

I have not understood what the AC load line for a BJT is and while drawing the AC load line for a BJT, the collector emitter voltage VCE and the collector current IC are related as, IC = -VCE / (RC //...
248 views

### confusion regarding bias voltage of a transistor

"this dc voltage is known as bias voltage and it's ...regardless of the polarity of the signal source" now I have this question : **1.**Do i manually need to choose bias voltage so that so ...
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1 vote
190 views

### Gate voltage range - Biasing circuit

I am looking for Biasing circuits which can provide gate voltage in the range of -4V to -0.5V. In the application note of AMPLEON AN-11130, there is a table mentioning the specifications of the ...
1 vote
533 views

### Where do input bias currents flow and what voltage drops do they create?

I have asked this question (and answered it below) mainly as a continuation of the question, How does the compensation resistor in an inverting amplifier compensate for the input bias current?... but ...
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### Output Stage Stability

I've been reading over amplifier output stage design and hoped someone might be able to advise if my circuit has any fundamental flaws - or if there are any tweaks I should make that would bring ...
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1 vote
94 views

### Single supply amplifier biasing

I'm trying to understand this circuit. I can see that BW1 is a low pass filter and BW3 removes any DC from the output signal, but what does BW2 do? If it is acting as a filter, is it a high pass ...
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### op amp input biasing question: why wouldn't an input sensor draw current and get fried?

First post here, thank you in advance for all responses! In a nutshell, my question is, if you bias the input of an op amp, why doesn't current then flow from your biasing mechanism into whatever ...
119 views

### Why does current not flow through Rg?

I cannot seem to understand this. Please explain the Kvl part for this as well.
158 views

### Power amplifier - Drain voltage should be pulsed?

I am trying to bias the power amplifier QPA1022. I am planning to bias this amplifier by fixed gate voltage and pulsed drain voltage.For this I am using MABC-001000-DP000L for the same. I am unable to ...
467 views

### Biasing circuit - Voltage follower circuit

I am using MABC-001000-DP000L, which is and Bias controller/sequencer. I am using this for Providing gate voltage and drain voltage to the power amplifier. In the datasheet, it is mentioned that the ...