1 / 20

SEMICONDUCTORS

SEMICONDUCTORS. Transistor Amplifiers. SEMICONDUCTORS.

gwidon
Download Presentation

SEMICONDUCTORS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. SEMICONDUCTORS Transistor Amplifiers

  2. SEMICONDUCTORS • In the diagram below the battery is a variable voltage source and the voltage on the emitter side is designated as VEE, the voltage on the collector side is designated as VCC, and the transistor symbol is used with the designated letter Q. • These are standard labeling conventions.

  3. SEMICONDUCTORS • Given the formula IE = IB + IC which we covered in a previous lesson, then when IE doubles so too does IB+ IC, this happens because the three currents are proportional. • In order for a transistor to amplify a signal it must take the input signal and produce an output signal that is greater in strength or amplitude.

  4. SEMICONDUCTORS • The transistor can not do this if it is connected as shown. • In this configuration IE = IB + IC there is no amplification

  5. SEMICONDUCTORS • If we add a load resistor between the collector and the positive side of the collector battery (VCC ) we can produce a specific voltage drop. • We have also separated the negative terminal of VEEfrom the emitter.

  6. SEMICONDUCTORS • We are now providing an input voltage between the emitter and the emitter voltage source. • If a small voltage is applied to the input terminals it will increase the value of VEE, which will cause IE and Ic to increase and will also cause the voltage drop across RL to increase.

  7. SEMICONDUCTORS • If the input voltage is reversed so it opposes VEE, then the value of VEE is reduced and both IE and Ic will decrease. • This will cause the voltage drop RL to decrease, but the output voltage change will be much greater than the input change.

  8. SEMICONDUCTORS • This is because the output voltage is developed across a high output load resistance RL and the input voltage is applied to the low resistance offered by emitter junction. • A very low input voltage can control the value of IE and IC, IC is forced through a higher resistance and produces a higher output voltage.

  9. SEMICONDUCTORS • There are three different circuit configurations for transistors to provide amplification. • The common base circuit • The common emitter circuit • The common collector circuit

  10. SEMICONDUCTORS • In each one of these circuits one of the three leads is used as a common lead which is typically connected to ground. • The circuits are then referred to as grounded base, grounded emitter and grounded collector circuits. • In each of these configurations the emitter junction is always forward biased while the collector junction is reverse biased.

  11. SEMICONDUCTORS • In the common base circuit the transistor’s base region is used as a common reference point and the emitter and collector serve as the input and the output connections.

  12. SEMICONDUCTORS • The common base circuit provides voltage amplification, and offers low input resistance and high output resistance. • This circuit produces a slightly less output current than the input current but more output power (P=IxE).

  13. SEMICONDUCTORS • In the common emitter circuit the voltage is applied to the base and referenced to the emitter and the output is developed across the collector and the emitter.

  14. SEMICONDUCTORS • The emitter junction of each transistor is still forward biased and the collector junction is still reverse biased.

  15. SEMICONDUCTORS • The forward biased voltage VBB is now applied to the base instead of the emitter. • The forward biased voltage VCC controls the base current IB instead of the emitter current IE.

  16. SEMICONDUCTORS • The common emitter circuit provides a higher output for given input. • The common emitter circuit is the only circuit that provides voltage, current and power amplification. • The common emitter circuit configuration is the only circuit capable of 180 degree phase shift between the input and output signals.

  17. SEMICONDUCTORS • In the common collector circuit the collector is the reference point and the base is the input and the emitter is the output.

  18. SEMICONDUCTORS • In the common collector circuit the input signal is applied between the base and the collector and the output voltage is developed across the load which is connected between the emitter and collector regions.

  19. SEMICONDUCTORS • The emitter current IE flowing through the load is much greater than the base current IB, this provides an increase in current between the input and output terminals. • The output voltage at the emitter tends to track or follow the input voltage applied to the base. • For this reason the common collector circuit is often called an emitter follower.

  20. SEMICONDUCTORS • The common collector circuit is not useful as a voltage amplifier, it has a high input resistance with a low output resistance. • The common collector circuit serves as an impedance matching transformer and is sometimes referred to as an isolation circuit or buffer circuit.

More Related