AMPLIFIERS

AMPLIFIERS

1. Operational amplifiers

   • HIstory
     • 1930: first idea of Harry Black
       • 1941: first patent of Bell labs
     • U.S. army used it to calculate gun crews to hit a target
   • Uses
     • Past
       • Basic mathematical operations in analog computers
     • Present
       • Most of the electronic equipment such as : filters, AD/DA converters, comparators
   • Electronic features
     • -High input impedence -High open-loop gain -Low output impedence
     • Integrated circuits
       • -Two input pins (non inverting/inverting) -One output pin -Two supply pins -Two offset regulation pins
   • Benefits
     • -Low cost -Versatile -HIgh performance

2. Different types of amplifiers

   • Differential
     • Amplify the difference between two voltages
     • Used in circuits with negative feedback in one input
   • Linear
     • Output is proportional to the input but it delivers more power into a load
     • The output must be a faithful reproduction of the input
   • Audio
     • Require low level input
     • Amplify low power audio signal
     • Used in loud speakers

3. What are amplifiers?

   • Electronic device that increases the voltage, current or power of a signal
   • Main characteristics
     • Gain
       • It's the increase in signal power and it's expressed in decibel
     • Efficiency
       • Measure of how much power the system needs
     • Bandwidth
       • Range of frequencies in which the amplifiers work fine
     • Cascade application
       • Used when 1 amplifier is not enough to give good performance. So 2 or more amplifiers are connected together to create a singular big gain
   • Classifications
     • Power amplifiers made with bipolar transistor
     • Weak-signal amplifier made with FET
   • Noise and distortion
     • Undesirable signal that can degrade the desired signal
     • To avoid this problem it's commonly used the negative feedback