Generally we think of Amplifiers as audio amplifiers in the radios, CD players and stereo’s we use around the home. In this amplifiers summary section we looked at the amplifier circuit based on a single bipolar transistor as shown below, but there are several different kinds of transistor amplifier circuits that we could use.
Typical Single Stage Amplifier Circuit
Amplifiers Summary of Small Signal Amplifiers
- Small Signal Amplifiers are also known as Voltage Amplifiers.
- Voltage Amplifiers have 3 main properties, Input Resistance, Output Resistance and Gain.
- The Gain of a small signal amplifier is the amount by which the amplifier “Amplifies” the input signal.
- Gain is a ratio of output divided by input, therefore it has no units but is given the symbol (A) with the most common types of transistor gain being, Voltage Gain (Av), Current Gain (Ai) and Power Gain (Ap)
- The power Gain of the amplifier can also be expressed in Decibels or simply dB.
- In order to amplify all of the input signal distortion free in a Class A type amplifier, DC Base Biasing is required.
- DC Bias sets the Q-point of the amplifier half way along the load line.
- This DC Base biasing means that the amplifier consumes power even if there is no input signal present.
- The transistor amplifier is non-linear and an incorrect bias setting will produce large amounts of distortion to the output waveform.
- Too large an input signal will produce large amounts of distortion due to clipping, which is also a form of amplitude distortion.
- Incorrect positioning of the Q-point on the load line will produce either Saturation Clipping or Cut-off Clipping.
- The Common Emitter Amplifier configuration is the most common form of all the general purpose voltage amplifier circuit using a Bipolar Junction Transistor.
- The Common Source Amplifier configuration is the most common form of all the general purpose voltage amplifier circuit using a Junction Field Effect Transistor.
BJT Amplifier to JFET Amplifier Comparison
Parameter |
Common Emitter
Amplifier |
Common Source
Amplifier |
Voltage Gain, ( AV ) |
Medium/High |
Medium/High |
Current Gain, ( Ai ) |
High |
Very High |
Power Gain, ( AP ) |
High |
Very High |
Input Resistance, ( Rin ) |
Medium |
Very High |
Output Resistance, ( Rout ) |
Medium/High |
Medium/High |
Phase Shift |
180o |
180o |
Amplifiers Summary of Large Signal Amplifiers
- Large Signal Amplifiers are also known as Power Amplifiers.
- Power Amplifiers can be sub-divided into different Classes, for example:
- Class A Amplifiers – where the output device conducts for all of the input cycle.
- Class B Amplifiers – where the output device conducts for only 50% of the input cycle.
- Class AB Amplifiers – where the output device conducts for more than 50% but less than 100% of the input cycle.
- An ideal Power Amplifier would deliver 100% of the available DC power to the load.
- Class A amplifiers are the most common form of power amplifier but only have an efficiency rating of less than 40%.
- Class B amplifiers are more efficient than Class A amplifiers at around 70% but produce high amounts of distortion.
- Class B amplifiers consume very little power when there is no input signal present.
- By using the “Push-pull” output stage configuration, distortion can be greatly reduced.
- However, simple push-pull Class B Power amplifiers can produce high levels of Crossover Distortion due to their cut-off point biasing.
- Pre-biasing resistors or diodes will help eliminate this crossover distortion.
- Class B Power Amplifiers can be made using Transformers or Complementary Transistors in its output stage.
An input 220v ac to a transistor, and 100dc input base, how much would be emitter, is only DC applied to base?
GRAZIE OTTIMO INSEGNAMENTO
Hello, good morning.
I’m looking for a tutorial like this, but about “Class C Amplifiers BJT and FET Transistors”.
Could you help me, please ?
Thanks
i would like the circuit and wiring diagram for a 3volt disc cell , three transistor amp for electret to headphone amp. thank you
Dear I want to amplify 10mv to 60 mv signal in 0-5v signal… Can I do it with above mentioned circuit? Plz reply me.
Thanks
No
Helpful to understand circuit s
For speakerphone which amplifier circuit is suggested.
I got better information from your website
It helps
Another great page, thank you. (The link from this page to the next one is currently skipping chapters 9, 10 and 11. (I have just reported a similar problem in the 7th page where the link to the next one skips the 8th page, I’m not going to bother you again on similar details.)
i need more information about ampliers
Brother pls make this website as Android App it ll b helpful fr us to learn easy through an app
my amp power stop whenever I switch it on it can be on for just two seconds.
It is very helpful t understand about Amplifiers and our knowledge level is inc. about study
Really helpfull when no books r there with us…nd also understadable…
I hope to learn more with your assistance.
thanks.was very helpful
This tutorials are very effective and understandable by anytype of students.. Also please try to add more problems regarding the topics.