Questions tagged [biasing]

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75 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, ...
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1answer
69 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 ...
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1answer
68 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 ...
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3answers
75 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 ...
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3answers
75 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, ...
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0answers
65 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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1answer
48 views

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 ...
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0answers
53 views

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 ...
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2answers
136 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 //...
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2answers
88 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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0answers
23 views

Biasing circuit schematic clarifications

I am designing a biasing circuit using application note from AMPLEON. I have following doubts on which I need clarifications:- The switch S1 functionality in this circuit. I understood the ...
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1answer
153 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 ...
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1answer
255 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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0answers
62 views

Gate Voltage dropping under load condition

We have designed a custom board using the MABC_001_DP000L. We are Using this custom board to provide Biasing voltages to the QPA1022 Amplifier. We tested the custom board with the following set-ups:- ...
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0answers
66 views

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 ...
1
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0answers
34 views

Display port auxiliary signals biasing

I am using display port interface in my design. As per display port specification biasing circuit is implemented to auxiliary signals. Since AUXP and AUXN are LVDS signals they can be connected to 1....
1
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1answer
86 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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0answers
35 views

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 ...
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2answers
89 views

Why does current not flow through Rg?

I cannot seem to understand this. Please explain the Kvl part for this as well.
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0answers
49 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 ...
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1answer
357 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 ...
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2answers
200 views

Why can we bias MOSFET with current source?

My question is: If I have properly set VGS to prevent MOS from turning off, then if we biase a MOSFET with a constant current source, how can we conclude that it is working at saturation region? How ...
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0answers
72 views

Biasing circuit schematic - MABC-001000-DP000L [duplicate]

I am trying to design a bias controller circuit using MABC-001000-DP000L. I am unable to find the full schematic of the same. Has any one used MABC-001000-DP000L for designing bias circuit? Edit:- I ...
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1answer
105 views

Biasing of CE amplifier with emitter resistor for specific gain

I am trying to design a Common-Emitter amplifier to the following specifications: Midband voltage gain of 50 Frequency range 100Hz to 20kHz Load \$5k\Omega\$ with a coupling capacitor (not shown ...
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1answer
36 views

finding transconductance for common source amplifier

I wanted to check the transconductance formula I am using is correct when I am dealing with an amplifier that has a small signal (Vsig) and a DC signal(Vs). The schematic below is a little unclear but ...
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1answer
27 views

Can I use a buffer on my bias voltage net?

I'm a french stompbox / bass guitar pedal hobbyist, probably very bad at designing them. I've been thinking about bias voltage nets for some time, and how inefficient they sometimes are. I've studied ...
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3answers
101 views

Class C Amplifier: Calculating the base resistor

I've built a Class C amplifier for educational purposes and believe I understand the major concepts on how it works. The only piece I'm struggling with is how to calculate for the base resistor. From ...
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1answer
79 views

Troubles with mic preamp for headphones with integrated microphone

I am designing a preamp intended to interface with a microphone in common headphones (e.g. apple earpods, or sony headphones with a microphone) which will then connect to my ADC's inputs. I've ...
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1answer
113 views

Confusion on operation of bipolar differential amp (long tailed pair)

Let's say there's a basic differential amp constructed with two npn BJTs. And a current source is working as the tail. The task I have is to amplify a small AC signal of around 1mV p-p, referenced to ...
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1answer
99 views

bias a signal with DC input coupling, but without attenuation?

I want to bias the analog signal present on an MCU output pin. This signal varies between 0v and ≃3V, I need to shift it down to -/+1.5V range. Most importantly, I need to keep any DC offset ...
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0answers
35 views

Common emitter biasing

A quick question on biasing a common emitter. I am given the following circuit and asked to derive several things. I am provided with the information that the transistor is in the active region, so it ...
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2answers
70 views

AC coupling of a transistor

So we assume to have proper bias currents flowing in both of the two transistors. What is claimed by books is that a capacitive coupling will not change the bias parameters. But, we know that a ...
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2answers
180 views

Emitter current and Early effect

I know that due to Early effect in a npn transistor the effective base width reduces.However I can't understand how this will lead to an increase in emitter current. Some sources say that the charge ...
2
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1answer
58 views

How and in what chronological order did different transistor biasing circuits arise?

On the wikipedia page for BJT biasing, there are about 4 different biasing methods discussed. I can analyze and understand each one of them, however I want to know how and in what order people came up ...
2
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2answers
114 views

Bias stabilization of a transistor

The instability of Collector current(Ic) of a transistor depends on three factors viz. Icbo, Vbe & Beta. Can you explain why Vbe decreases(by 2.5 mV/°C) with increase in temperature?
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0answers
37 views

BJT conceptual doubt

I was given this problem in a problem set. I want to ask what will the voltage at Base when \$ \beta \rightarrow \infty\$. My answer to the problem - When \$ \beta \rightarrow \infty\$ then width of ...
2
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5answers
276 views

About transistor biasing and coupling capacitors in ICs

I'm trying to understand how biasing works in ICs. When using discrete transistors we are told to bias them using polarization circuits typically made of voltage dividers. Then ac signal is introduced ...
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3answers
164 views

In a class C amplifier, how does RB biases the base of transistor?

In a class C amplifier, I read that: "Resistor Rb is connected to the transistor Q1 base. A biasing resistor which connects to the base of Q1 try to pulls the base of transistor further downwards and ...
2
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2answers
742 views

Working of a transistor in a TTL inverter circuit

I was referring to TTL inverter circuit in the book Digital fundamentals by Thomas Floyd and its working principles first proposition went as follows: When input is HIGH, Base emitter of Q1 is ...
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1answer
81 views

Biasing a emitter follower darlington configuration

Below picture is a simple voltage regulator(link to simulator): The current at the op amps output is at nA region(why?), how can I increase the current at the op amps output without adding a third ...
2
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0answers
37 views

Initially on Power Control with BJTs

I've removed a voltage regulator from my circuit and replaced it with a series of BJTs. The regulator was just switching voltage. But I need the circuit (which happens to power/wake the micro) to be ...
0
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1answer
58 views

How to use a SPDT with no negative capability for audio signal routing?

I have a couple of SGM3005 chips and want to use them as switches in an audio circuit, but they don't support negative signals. The classical solution would be to bias the COM1 input, right? But, what ...
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3answers
108 views

Need Help debugging Colpitts oscillator

I've built the circuit shown in the picture on the breadboard. The simulation works as expected but when I build it i don't get any oscillations. I've measured all the DC voltages and they are as ...
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0answers
70 views

How does Q point affect gain

Let’s say I have a transistor class A amplifier circuit using a depletion mode FET. I have the load and the source resistor values already picked out to provide the right amount of gain and the source ...
0
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2answers
108 views

Differential amplifier with a current source

How to change the current source in the emitter here, so that the whole thing can be biased from a positive power supply (without the need for negative rail Vee) keeping all the other parameters more ...
0
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1answer
134 views

How to calculate cutoff frequency for a high pass filter in DC biasing circuit

I would like to DC bias an AC signal using a voltage divider as shown in the following schematic. I realise the bias point would be subject to noise from the power rails, but that is not a concern for ...
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7answers
1k views

Emitter resistor and biasing voltage

In many articles regarding transistor biasing I see a circuit like below and I don't really get what is the point of biasing like this WITHOUT emitter resistor Re? When emitter branch is connected ...
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2answers
424 views

Howland current source with voltage reference [closed]

I need a precision current pump for small ac signals(50uA) and i tried it in multisim with a howland topology. It works however i need the load to not be grounded but bound to a bias voltage. Here i ...
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1answer
87 views

Why is the effective base resistance important for the voltage divider BJT amplifier?

I came across many questions regarding the below type of biasing where they explain and analyze Rth Vth and conclude that Rth must be very small comparing to Rin. Rin is the effective resistance seen ...
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4answers
422 views

What exactly is meant by beta dependence in this fixed bias BJT scheme? [duplicate]

What I understand that, in a fixed bias BJT scheme the problem is beta dependence. Below is an example from a text: Now I read that this is not a good design. But I will still solve this by assuming ...