Analog electronics[EC0342] Question Bank Answers Part A UNIT-I ANALYSIS AND DESIGN OF SMALL SIGNAL LOW FREQUENCY BJT AMPLIFIERS 1).What is the main applications of CC amplifier and why? [2M, May 2016] CC - common collector commonly used as unity gain buffer and sometimes called emitter follower. It provides high input impedance, low output impedance and high bandwidth. Perfect for driving heavy loads.The drawback is no gain; gain is close to but less than one. Therefore, it is typically used in conjunction with an amplifier and not instead of an amplifier. CC is also used as a voltage translation stage . 2).What are the conditions for approximate h - parameter model? [3M, May 2016] Simplified common emitter hybrid model h-parameter In most practical cases it is appropriate to obtain approximate values of A V , A i etc rather than calculating exact values. How the circuit can be modified without greatly reducing the accuracy. figure shows the CE amplifier equivalent circuit in terms of h-parameters Since 1 / hoe in parallel with RL is approximately equal to RL if 1 / hoe >> RL then hoe may be neglected. Under these conditions. Ic = hfe IB . hre vc = hre Ic RL = hre hfe Ib RL .
Since h fe.h re » 0.01, this voltage may be neglected in comparison with h ic Ib drop across h ie provided RL is not very large. If load resistance RL is small than hoe and hre can be neglected. Output impedence seems to be infinite. When Vs = 0, and an external voltage is applied at the output we fined Ib = 0, I C = 0. True value depends upon RS and lies between 40 K and 80K. 3).What is base spreading resistance? [2M, May 2016] base spreading resistance a BJT is normally operated in FR mode, that is the base-emitter junction is forward biased and base-collector junction is reverse biased. In a bipolar junction transistor, the resistance in series with the base region due the body or mass of the region, as opposed to that associated with a junction. to 4).What is the high pass capacitor and why it is connected in CE amplifier? [3M, May 2016] For the bypass capacitor, A considerable reason for including the bypass caps is to provide an AC ground. This happens because , the AC signal will pass through the Capacitor Ce and bypass the resistor , making the apparent resistance zero. Consider the Voltage gain equation derived using KVL & Ohms law. If Re=0 , Them the gain becomes -gm*Rc , which is actually larger than the previous gain. Also the DC biasing isn't affected, due to presence of Re.
This reason is very much appealing and seems to be perfect. Bypass capacitors , passes all the high frequency noise which is prevalent in the circuit due to floating DC levels . Thus it provides ground to the high frequency noise present in the circuit .So Bypass capacitor , also helps to remove Noise ! 5). State and explain Miller’s theorem? [2M, May 2015] The introduction of an impedance that connects amplifier input and output ports adds a great deal of complexity in the analysis process. One technique that often helps reduce the complexity in some circuits is the use of Miller's theorem. Miller's theorem applies to the process of creating equivalent circuits. This general circuit theorem is particularly useful in the high-frequency analysis of certain transistor amplifiers at high frequencies. 6).How are amplifiers are classified on their duration of transistor conduction? [3M, May 2015] Amplifiers are classified on their duration of transistor conduction Class A, Class B, Class AB, Class D. 7). Write the significance of gain and bandwidth product of an amplifier? [2M, May 2015]
It is informative to calculate the product of the magnitude of the midband gain and the bandwidth to obtain the gain-bandwidth product, or GBW: Where