1 / 27

Chapter 8

Chapter 8. Introduction to Amplifiers. Amplifier Properties. Amplifiers have three fundamental properties: Gain Input Impedance Output Impedance. Gain. Gain – A multiplier that exists between the input and output of a circuit. There are three types of gain. Voltage gain ( A v )

queenr
Download Presentation

Chapter 8

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. Chapter 8 Introduction to Amplifiers

  2. Amplifier Properties • Amplifiers have three fundamental properties: • Gain • Input Impedance • Output Impedance

  3. Gain • Gain – A multiplier that exists between the input and output of a circuit. • There are three types of gain. • Voltage gain (Av ) • Current gain (Ai ) • Power Gain (Ap ) • Amplifiers are designed to provide one or more types of gain.

  4. Voltage Gain (Av ) • Voltage gain – The ratio of output signal voltage to input signal voltage. • Because it is the ratio of one voltage to another, voltage gain has no unit of measure.

  5. General Voltage Amplifier Model • The voltage amplifier model represents output voltage as the product of voltage gain and input signal voltage (Avvin).

  6. Amplifier Input Impedance (Zin) • Input impedance – The load that an amplifier places on its source.

  7. Output Impedance (Zout) • Output impedance – The “source impedance” that an amplifier presents to its load.

  8. The Ideal Voltage Amplifier • The ideal voltage amplifier would have: • Infinite gain (if needed) • Infinite input impedance • Zero output impedance

  9. The Current Amplifier Model • The general model of a current amplifier includes the circuit • Input impedance (Zin) • Output impedance (Zout) • Current gain (Ai )

  10. The Ideal Current Amplifier • The ideal current amplifier would have • Infinite gain (if needed) • Zero input impedance • Infinite output impedance

  11. Common-Emitter Amplifiers • The emitter is common to the input and output circuits. • The transistor emitter is returned to ac ground. • The input and output signal voltages are 180° out of phase.

  12. Common-Emitter Amplifiers • Common-emitter amplifiers typically have • High power gain (> 1000) • Midrange input impedance (Between 1 kW and 10 kW) • Midrange output impedance (Between 1 kW and 10 kW)

  13. Common-Collector Amplifiers • The collector terminal is common to the input and output circuits. • The input and output signal voltages are in phase. • Also known as an emitter follower, because the emitter (output) signal closely follows the base (input) signal.

  14. Common-Collector Amplifiers • Common-collector amplifiers typically have • Low voltage gain (< 1) • Midrange current gain • High input impedance (> 10 kW) • Low output impedance (< 1 kW)

  15. Common-Base Amplifiers • Common-base amplifiers typically have • Low current gain (< 1) • Midrange voltage gain • Low input impedance (< 1 kW) • High output impedance (> 10 kW)

  16. Amplifier Efficiency (h) • Efficiency – The percentage of the power drawn from the dc power supply that an amplifier actually delivers to its load. • The ideal amplifier would be 100% efficient. • Efficiency, as a percentage, is found as

  17. Distortion • Distortion – Any undesired change in the shape of a waveform. • Two common types of distortion are • Nonlinear distortion • Crossover distortion

  18. Class A Amplifiers • A class A amplifier has • An active device that conducts during the entire 360° of each input cycle. • An output that contains little or no distortion. • A maximum theoretical efficiency of 25%. • Class A amplifiers are typically used as small-signal (low-power) amplifiers because of their low efficiency ratings.

  19. Class B Amplifiers • A class B amplifier contains two transistors that each conduct for 180° of the input cycle. A class B amplifier has: • An output that contains little or no distortion. • A maximum theoretical efficiency of 78.5%.

  20. Class AB Amplifiers • A class AB amplifier contains two transistors that each conduct for slightly more than 180° of the input cycle. • Also referred to as a diode-biased amplifier.

  21. Class C Amplifiers • A class C amplifier has • An active device that conducts during less than 180° of each input cycle. • An output that may contain a significant amount of distortion. • A maximum theoretical efficiency of approximately 99%.

  22. Class C Amplifiers • A class C amplifier • Contains an LC circuit rather than a collector resistor. • Is a tuned amplifier (one that produces a usable output for a specific range of frequencies).

  23. Decibels (dB) • Decibel (dB) – A logarithmic unit used to express the ratio of one value to another. • Decibels make it possible to easily represent very large and very small numbers.

  24. dB Power Gain Example: Convert Ap = 1200 to dB form.

  25. dB Power Gain (Cont.) Example: Convert 25 dB to standard numeric form.

  26. dB Voltage Gain Example: Convert Av = 120 to dB form.

  27. dB Voltage Gain (Cont.) Example: Convert 12 dB to standard numeric form.

More Related