JFET and its configuration

-JFET (junction gate field effect transistor) that kind of transistor that’s main difference from the BJT (bi-polar transistor) is that BJT can be considered as current control devices (dependent current source) while the JFET can be considered as voltage control device.
There are two types of JFET, the p-type JFET that consists of a middle channel of a semiconductor material having large number of positively charges carriers, while the N-type JFET that consists of a middle channel of a semiconductor material of negatively charged carriers.
Through this transistor the Electric charge passes through the channel from the source pole to the drain pole along the channel.

As shown here there are three terminals for the JFET, the Gate which controls the Electric current passes through the channel, the source which is the Source of electric charge and the Drain where the electric charge is collected.

So in this transistor as we apply some voltages at its terminals, V_GS = 0 v, V_DS = +ve voltage.

So at the channel which is N-type the electrons will be attracted to the drain which we apply a positive voltage at it, at the gate terminal which is P-type, by the applied voltages here we noticed that the p-type forms with the n-type a reverse bias which makes the depletion region larger and by increasing the drain source voltage V_DS the depletion region larges until it reaches a critical point where approximately no electric field can pass from the source to drain and that makes the resistivity of the device increase, this voltage is called the pinch-off voltage V_P, a small current can pass through the channel that us highly attracted to the drain terminal which called the saturation current I_DSS that passes through the channel when applying V_DS  ≥ V_P after exciding the pinch off voltage , the current will stay constant which will be I_DSS and its physical formula can be given by :

I_D = I_DSS (1-VGS/VP)^2

There are three types of connecting a JFET in a Circuit to do a certain function.

a.Common gate

This configuration provides a low input impedance while provides a high output impedance, although the voltage is high, but the current gain as well as the power gain are low, there is an advantage in this configuration is that the input and the output are in phase.  

b. Common drain

This configuration is known as source follower, as the source voltage follows the gate input voltage, that offers high input impedance and low output impedance, it is used as a buffer just to separate the input from the output,
The voltage gain here is one, the input voltage and the output one seems to have the same voltage, although the current gain is high, and the input and the output signals are in phase.

c.Common Source

This configuration is the most widely used as the common source circuit in general provides a medium input and output impedance, and both current and voltage gains can be described as medium, but the output signal is shifted by 180 degree (the out is the inverse of the input signal).

How the first transistor worked

The first transistor was invented at Bell Laboratories on December 16, 1947 by William Shockley (seated at Brattain's laboratory bench), John Bardeen (left) and Walter Brattain (right). This was perhaps the most important electronics event of the 20th century, as it later made possible the integrated circuit and microprocessor that are the basis of modern electronics.

Prior to the transistor the only alternative to its current regulation and switching functions (TRANSfer resISTOR) was the vacuum tube, which could only be miniaturized to a certain extent, and wasted a lot of energy in the form of heat. 
The picture on the left above shows the first point contact transistor built by Walter Brattain. It consisted of a plastic triangle lightly suspended above a germanium crystal which itself was sitting on a metal plate attached to a voltage source. A strip of gold was wrapped around the point of the triangle with a tiny gap cut into the gold at the precise point it came in contact with the germanium crystal. The germanium acted as a semiconductor so that a small electric current entering on one side of the gold strip came out the other side as a proportionately amplified current.

In this video, it is explained how the first transistor is build.

Difference between Microprocessor and Microcontroller

Microprocessor and Microcontroller are always designed for real time applications. they share many common features and at the same time they have significant differences. Both the IC’s i.e., the microprocessor and microcontroller cannot be distinguished by looking at them. They are available in different version starting from 6 pin to as high as 80 to 100 pins or even higher depending on the features.

Difference between microprocessor and microcontroller

Microprocessor is an IC which has only the CPU inside them i.e. only the processing powers such as Intel’s Pentium 1,2,3,4, core 2 duo, i3, i5 etc. These microprocessors don’t have RAM, ROM, and other peripheral on the chip. A system designer has to add them externally to make them functional. Application of microprocessor includes Desktop PC’s, Laptops, notepads etc.

But this is not the case with Microcontrollers. It has a CPU, in addition with a fixed amount of RAM, ROM and other peripherals all embedded on a single chip. At times it is also termed as a mini computer or a computer on a single chip. Today different manufacturers produce microcontrollers with a wide range of features available in different versions. Some manufacturers are ATMEL, Microchip, TI, Freescale, Philips, Motorola etc.

Microcontrollers are designed to perform specific tasks. Specific means applications where the relationship of input and output is defined. Depending on the input, some processing needs to be done and output is delivered. For example, keyboards, mouse, washing machine, digital camera , pen-drive, remote, microwave, cars, bikes, telephone, mobiles, watches, etc. Since the applications are very specific, they need small resources like RAM, ROM, I/O ports etc and hence can be embedded on a single chip. This in turn reduces the size and the cost.

Microprocessor find applications where tasks are unspecific like developing software, games, websites, photo editing, creating documents etc. In such cases the relationship between input and output is not defined. They need high amount of resources like RAM, ROM, I/O ports etc.

The clock speed of the Microprocessor is quite high as compared to the microcontroller. Whereas the microcontrollers operate from a few MHz to 30 to 50 MHz, today’s microprocessor operate above 1GHz as they perform complex tasks.

Comparing microcontroller and microprocessor in terms of cost is not justified. Undoubtedly a microcontroller is far cheaper than a microprocessor. However microcontroller cannot be used in place of microprocessor and using a microprocessor is not advised in place of a microcontroller as it makes the application quite costly. Microprocessor cannot be used stand alone. They need other peripherals like RAM, ROM, buffer, I/O ports etc and hence a system designed around a microprocessor is quite costly.