EE599-020AudioSignalsandSystems

1、EE599-020Audio Signals and SystemsAmplifiersKevin D. DonohueElectrical and Computer EngineeringUniversity of Kentucky1Related Web SitesThe understanding and design of amplifiers are primarily the domain of electrical engineers and technicians. Web sites below related to the design and characterizati

2、on of amplifiers:2Preamplifier Amplify small signals to intermediate levels while maintaining good SNR and fidelity. Sometimes performing compression (nonlinear / logarithmic transfer characteristic to prevent hard clipping). Intermediate Stage Amplifier Amplify and process intermediate level signal

3、s with good SNR for mixing, equalization, compression, expansion, and other signal processing effects. Power Amplifier Amplifies high SNR intermediate level signals to high power levels for driving electro-acoustic transducers.Amplifier Usage in Audio3Efficiency Output power over Input power (includ

4、ing that of the power supply). Distortion Total harmonic distortion (THD). For sinusoidal signal inputs, THD is the ratio of power at harmonic frequencies (excluding the fundamental) of the output signal over the total output signal power.Fidelity Flatness of frequency response characterized by freq

5、uency range and transfer function variation in that range. Amplifier Performance 4Class A - Low distortion, bad efficiency. Output stage with single transistor requires DC biased output (10-20% efficiency).Class B - Crossover distortion, good efficiency. Output stage has 2 transistors so bias curren

6、t is zero (80% efficient).Class AB Reduced crossover distortion, good efficiency. Output stage has 2 transistors with biasing to push signal out of crossover distortion range. Class D Moderate distortion, high efficiency, operates in switch mode. Good for battery driven applications.Amplifier Classe

7、s5Given the transfer characteristic for a class B amplifier below, compute the THD for a 3 volt input sinusoid. Example VinVout0.6v-0.6v7v3v-7v-3v6Given the transfer characteristic for a class AB amplifier below, compute the THD for a 3 volt input sinusoid. Example VinVout7v3v-7v-3v1.75v-1.75v7Compr

8、ession: In order to improve the dynamic range of a system without overdriving the amplifiers (or other elements in the system) resulting in hard clipping, a softer clip can be applied to more gradually compress the signal amplitude as it approaches the saturation limits of the system.Compressorswher

9、e is between 0 (hard clipping) and 1 (no compression).8Expansion: In order to improve the dynamic range of a system by reducing low level signal inputs, a lesser gain can be applied to the signal components below a certain threshold and a normal linear gain can be applied to signal levels above the threshold.Expanderswhere is between 1 (no attenuation) and (complete attenuation - behaves as a gate).9ExamplePlot the tr