1 / 24

Common Base and Common Collector Amplifiers

Common Base and Common Collector Amplifiers. Reminder: BJT Small Signal Model. B. C. i c. i b. r .  i b. i e. E. Amplifier. Definition of input and output voltage and current directions. i in. i out. v in. v out. Common Base Amplifiers.

Download Presentation

Common Base and Common Collector Amplifiers

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. Common Base and Common Collector Amplifiers

  2. Reminder: BJT Small Signal Model B C ic ib r ib ie E

  3. Amplifier Definition of input and output voltage and current directions iin iout vin vout

  4. Common Base Amplifiers • Uses the same stabilised bias scheme as CE configuration.

  5. Common Base Amplifiers • Uses the same stabilised bias scheme as CE configuration. • The base is grounded for a.c. signals using a large capacitor. • Signal input at the emitter (between the emitter and the common base) • Signal output at the collector (between the collector and the common base)

  6. +VCC RE GND Common Base Amplifiers R1 RC RL vout R2 CB vin

  7. We will ignore the a.c. coupled load RL vout vin +VCC RE GND Common Base Amplifiers R1 RC R2 CB

  8. CB Amplifier, a.c. equivalent. iin E C ic= iout ie ib vout vin RC RE r ib B

  9. Common Base Amplifier

  10. Common Base Amplifier

  11. Input impedance to transistor Common Base Amplifier

  12. Common Base Amplifier iin E C ic= iout ie ib vout vin RC vin RE r ib B

  13. Input impedance to stage (whole amplifier) Common Base Amplifier

  14. Common Base Amplifier iin E C ic= iout ie ib vout vin RC RE r ib B

  15. Common Collector Amplifier • Signal input between base and common collector. • Signal output between emitter and common collector.

  16. Common Collector Amplifier VCC R1 R2 vin RE vout

  17. ib io B r RS ib RE vs C CC Amplifier, a.c. equivalent circuit ie E RB = R1//R2 vin vout

  18. Common Collector Amplifier

  19. Common Collector Amplifier • Transistor input impedance =

  20. Common Collector Amplifier

  21. Common Collector Amplifier

  22. To find the output impedance we note that: Hence Common Collector Amplifier

  23. Common Collector Amplifier • The voltage gain is slightly less than unity. • The CC circuit is sometimes known as an emitter follower since the output voltage at the emitter follows the input voltage at the base.

  24. Common Collector Amplifier • The prime function of this circuit is to connect a high resistance source to a low resistance load (“a buffer amplifier”). • Since voltage gain is approximately one this is achievable as the current gain is high.

More Related