Monday, September 29, 2014

The Most imp part of Satellite Receivers “Common Source Amplifier”

As we all know the satellite receiver is the most imp part of Wireless Communication system, but we usually not thinks too much about the internal part functioning. In this blog I have covered one of its most imp parts (Common Source Amplifier) theoretical or technical background.  

Satellite communication Block diagram with common source amplifier
A common-source amplifier is one of three basic single-stage field-effect transistor (FET) amplifier topologies, typically used as a voltage or transconductance amplifier. The easiest way to tell if a FET is common source, common drain, or common gate is to examine where the signal enters and leaves. The remaining terminal is what is known as "common". In this example, the signal enters the gate, and exits the drain. The only terminal remaining is the source. This is a common-source FET circuit.

Common Source Amplifier
Small Signal model of common source Amplifier

The common-source (CS) amplifier may be viewed as a transconductance amplifier or as a voltage amplifier.As a transconductance amplifier, the input voltage is seen as modulating the current going to the load. As a voltage amplifier, input voltage modulates the amount of current flowing through the FET, changing the voltage across the output resistance according to Ohm's law. However, the FET device's output resistance typically is not high enough for a reasonable transconductance amplifier (ideally infinite), nor low enough for a decent voltage amplifier (ideally zero). Another major drawback is the amplifier's limited high-frequency response. Therefore, in practice the output often is routed through either a voltage follower (common-drain or CD stage), or a current follower (common-gate or CG stage), to obtain more favorable output and frequency characteristics. The CS–CG combination is called a cascode amplifier.

Common source amplifier characteristics

        Amplifier Characteristics

         Voltage gain
·         Medium

        Current gain
·         Medium

         Power gain
·         High

                Input / output phase relationship
·         180°

         Input resistance
·         Medium**

         Output resistance
·         Medium

  Tags : Common source amplifier      SPICE Training       HPSICE           PSPICE      Analog VLSI Design

Author - Amresh Kumar Singh
(Trainee Engineer at Silicon Mentor)