Conclusion After Af ter conducting the experiment, the following conclusions were we re gathered. * Ampliers are very helpful in increasing a small signal, whether its voltage, current or power to become a larger signal. * A small-signal amplier only uses a small part of it load line under signal conditions. * The The volt voltag age e gain gain of smal smalll-si sign gnal al ampl ampli ier ers s is comp comput uted ed by gett gettin ing g the the uotient of the output voltage and its input voltage. * The common-base small-signal amplier is the best for amplifying voltage because it has the greatest voltage gain. * The common-emitter small-signal amplier is the second highest voltage gain amon among g the the thr three ampl ampli ier ers s and and it sh show ows s a !" !"# # degr degree ee phase hase di di$e $errence ence between the input and the output. * The common-collector small-signal amplier has the smallest voltage gain and does not show phase di$erence between the input and output signals. * A commom-collector amplier is also called and emitter-follower. emitter-follower. * %n a small-signal amplier, the base and the collector has only one function, each acts as input and output respectively while the emitter can act as an input or and output. * The transistor operates in the active region if and only if the base-emitter &unction is forward-biased and the base-collector &unction is reversed-biased, if satised, it will serve as an amplier. amplier. * %n a common-collector small-signal amplier, the collector is the common terminal to an ac signal or ground in which the base serves as the input while the emitter serves as the output. * %n a common-emitter small-signal amplier, the emitter is common terminal to an ac signal or ground in which the base serves as the input while the collector serves as the output. * %n a common-base small-signal amplier, the base is common terminal to an ac signal or ground in which the emitter serves as the input while the collector serves as the output.
* A common-emitter amplier has high voltage, current, and power gains, but it has relatively low input resistance. * A common-collector amplier has high input resistance and high current gain, but its voltage is approximately eual to !. * The common-base amplier has a high voltage gain, but it has a very low input resistance and its current gain is approximately eual to !. * 'or an ()( transistor, the base-emitter &unction is forward-biased and it is approximately eual to #.+. * 'or an ()( transistor, the base-collector &unction is reversed-biased if the collector voltage is greater than the base voltage.
nterpretation of esults The main ob&ective of xperiment ! entitled /mall /ignal Amplier is to improve the students 0nowledge of 12T ampliers. +oltage divider bias is utili3ed as the biasing of the circuits. n relation to our experiment, we ve utili3ed three circuits for ampliers, namely the common-base, commoncollector, and common-emitter. All of them have specied functionalities depending on your ob&ective in utili3ing them. “
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n the gathering of data, each amplier was analy3ed and observed under two operating conditions, 4C ad AC. n a common-base amplier we have observed the gap between the voltages drops across the collector, which is the expected output, and the emitter, which it he expected input is considerably large. 'urthermore, the voltage gain of the common base amplier was found to be the largest among the three types used. This was further proven by using the AC source which was visuali3ed using an oscilloscope. %bserving, the capacitors play an essential role in the circuit. 1y inspection, using the bypass capacitor would eliminate the parallel resistors to it which are ! and 5. n the next circuit which is the common emitter amplier, it exhibits less amplication in comparison to the common-base amplier. This is expected because of the doping concentration of every layers of the transistor. The circuit still has a large amplication. The behavior can be observed by simply
loo0ing at the voltage drops across the input terminal 6base7 and the output terminal 6collector7. 1y observing the circuit, we could see that there is no bypass capacitor used that is supposed to be connected at the collector terminal. %n the other hand, if so the circuit would be connected in such a manner, the emitter resistor would be shorted since at AC operation, all current would pass through the shorted capacitor. All in all, an amplier li0e this is usually used when amplication of the current and voltage is necessarily in balanced scales. 8astly, a common-collector amplier in comparison to the previous ampliers based on the data we have gathered produces the least gain for voltage. 1ecause of this, this type of amplier is usually used as a bu$er. %btaining the ration between the input and output voltages, we will see that it is approximately eual to one because of the reason that the values are almost the same. Concurring, this type of amplier is not ideal when you want to amplify the input voltage of the circuit. 9owever, this amplier is mainly used for amplifying current as observed in the data gathered.
/ample Computations
)art ! : Common-1ase Amplier +i ;!#+i ; ".=#+>!#
)art 5 : Common-mitter Amplier +i ;!#+i ; -!.<<+>!#
)art @ : Common-Collector Amplier +i ;!#+i ; !#!#
raphs and Curves
raph !-!. /ignal Baveforms of Common-1ase Amplier
raph !-5. /ignal Baveforms of Common-mitter Amplier
raph !-@. /ignal Baveforms of Common-Collector Amplier
