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# [SOLVED]HELP....BASICS OF TRANSISTORS(Any help will be appreciated!)

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#### anuragmash

##### Junior Member level 1
I understood the transistor action(emitter-base voltage acts like a gate and allows more electrons to diffuse into the collector region and the voltage applied to collector acts like a suction to **** all the electrons) but now when we have different configurations such as "Common" Emitter and "Common" Base,
1) I don't understand what is the difference between the two!!!
2) In both the cases the base-emitter region is forward biased and collector base reion is reverse biased. So what is the difference between the two??
3) How does the common terminal control the current between the other two regions?
4) What do you mean by grounding? Please help me visualize!!!!
PLEASE HELP!!!!!!!!!!!!!!!!!!!!!

Refer this

**broken link removed**

majerio

### majerio

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What you have described is the physical operation of transistors - they need base to be more positive than emitter and collector to be more positive than base (for npn). When it comes to the different configurations CB, CE, CC - these are not meant to alter that physical operation. You should probably make a distinction between physical conditions vs circuit configurations. But always the current is controlled by the Vbe, no matter what the configuration is.
Grounding or grounded terminal is the one that is connected to circuit ground or to a point that has only DC potential and no ac voltage - like for example Vcc (supply). In the CE, the emitter is grounded i.e. connected to the common point aka ground. There is an exception to that when we talk about CE with emitter degeneration. In CB, the base is connected to ac ground and in CC or emitter follower - collector is connected to the ac ground.
The difference between CE and CB for example is that the signal in CE is applied to the base - since emitter is at ac gnd it is not moving with the signal. The output signal you get from the collector. A consequence of this is that the input impedance at the base is "high" and the output impedance at the collector is high and you get voltage and current gain and the stage is inverting. In the case of CB, input is applied to the emitter since base is connected to ac ground and is not moving with the signal. Impedance at the emitter is low and so is the input impedance of the stage. The output impedance at the collector is the same as int he CE case i.e. kind of high. With CB you get no current gain, only voltage gain and it is not inverting. In CC you apply the signal at the base and get it out at the emitter. As such you have high input impedance, low output impedance, no voltage gain and the stage is not inverting.

HI ANURAGMASH

> ALTHOUGH THERE IS NO DIFFERENCE IN THE BASIC OPERATION OF TRANSISTORS IN ANY MODE i>e INTERNALLY IF YOU LEARN THE MICROELECTRONIC DETAILS.
> NOW THE ONLY DIFFERENCE COMES THAT WHAT IS APPLIED AT THE INPUT AND WHAT IS THE OUTPUT.
TREAT THE TRANSISTORS AS CURRENT CONTROLLED DEVICES ALTHOUGH THEY CAN BE CONTROLLED BY THE VOLTAGE ALSO(ACTUALLY THIS IS A DOUBT FOR
ME TOO AS WHY THEY ARE TREATED AS CURRENT CONTROLLED AND NOT VOLTAGE CONTROLLED BESIDES HISTORICAL REASONS)
OK
COMMON BASE CONFIGURATION: INPUT IS Ie (EMITTER CURRENT) AND OUTPUT IS TE Ic (COLLECTOR CURRENT) . LOOK THE CURRENT GAIN i.e ALPHA(APPROX
UNITY). IF YOU LOOK AT THE VOLTAGE GAIN, IT WILL BE QUIET HIGH say 120 for ex.
SO POWER GAIN = 120 (APPROX)

COMMON EMITTER CONFIGURATION : I/P IS Ib (BASE CURRENT) AND O/P IS Ic (COLLECTOR CURRENT). CURRENT GAIN IS BETA SAY LOW VALUES OF AROUND 20
()WORST CASE) for ex AND THE VOLTAGE GAIN SAY AROUND 50 for ex.
SO POWER GAIN = 1000

SO ONE OF THE DIFFERENCE COMES IN THE GAINS SCENARIO DEPENDING UPON WHAT IS THE I/P AND O/P. THE INTERNAL FLOW OF CARRIERS IS ESSENTIALLY THE SAME IN ALL CONFIGs AND SAME SEMICONDUCTOR PHYSICS IS APPLICABLE INSIDE THE TRANSISTOR IN ANY CONFIGs. WHENEVER WE HAVE TO USE THE TRANSISTOR IN ACTIVE MODE , WE WILL ALWAYS FWD BIAS THE EMITTER JUNCTION AND REVERSE BIAS THE COLLECTOR JUNCTION.

OF COURSE THE OTHER DIFFERENCES LIE IN THE I/P , O/P IMPEDENCES AND O/P SIGNAL POLARITY w.r.t THE I/P SIGNAL . INTERNALLY YOU HAVEN'T CHANGED ANYTHING , SO THE TRANSISTOR WILL WORK AS IT WORKS IN THE CB CONFIG. WHICH YOU MIGHT HAVE STUDIED AT FIRST. THE ONLY CHANGE YOU MAKE IS IN THE OUTER CONFIGURATION , THE I/Ps AND THE O/Ps SO THAT THE CHARACTERISTICS CURVES ARE DISSIMILAR. WE CAN USE THE SAME TRANSISTOR FOR DIFFERENT CONFIGURATIONS BY CHANGING THE OUTER CONFIG.

>I DON'T KNOW OF THIS FACT THAT THE COMMON TERMINAL CURRENT HELPS IN CONTROLLING THE OTHER TWO CURRENTS. AS FAR AS I HAVE KNOWN TILL NOW, IT'S THE DOPING PROFILES, THE GEOMETRICAL SIZES, AND V OR I SOURCES THAT ARE APPLIED TO CONTROL THE FLOW OF ANY CURRENT WITHIN THE TRANSISTOR. SINCE ALWAYS Ie=Ib + Ic . AFFECTING ANY CURRENT WOULD EFFECT THE OTHER TWO NATURALLY BUT I THINK WHAT YOU MEAN IS THAT CONTROL OF Ib. THE BASE DOIPNG OR THE EFFECTIVE BASE WIDTH CONTROL BY REVERSE BIAS CAN CONTROL Ib.

>GROUND MEANS NOTHING EXCEPT TO MAKE THE POTENTIAL ZERO AND PRACTICALLY WE DO SO BY DEPOSITING LARGE COPPER BASE WHERE GND IS REQUIRED AS GND MEANS THAT IT HAS INFINITE CHARGE CARRIERS AND HUGE METAL DEPOSITS DO HAVE electrons IN ABUNDANCE JUST LIKE THE EARTH GND HAS INFINITE CHARGE.

I hope you know that capital letters are the equivalent of shouting. You can use lower case font like the rest of us [alexan_e]

Hello Sir
I am doing my thesis on Theoretical Analysis of Mos current mode logic(MCML) by using Cadence(Tool) Virtuoso .iam not getting results of simple inverter logic in MCML in both 180nm and 90nm tech with load as resitor and load as pmos in both cases .
And one more doubt plz in gpdk 180nm and gpdk 90nm technology how much vdd should give .In my thesis iam giving vdd=2.5v I think we can give upto 5v .what is the specification of vdd how it useful to design.if minimum gives what happend and if maxum?
i am attaching my schematic and waveforms please tell me where is error.
These schematics in Cadence Virtuoso 180nm technology:
Pmos as a load in MCML(Mos current mode logic)

Resistor as a load in MCML(Mos current mode logic)

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Basics of transistors

hiiiiiiii
can any one explain Differential amplifier plzzzzzzzzz.

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