Analysis of CE amplifier

Voltage gain:

To find voltage gain, consider an unloaded CE amplifier. The ac equivalent circuit is shown in the figure 1. The transistor can be replaced by its collector equivalent model that is a current source and emitter diode which offers AC resistance r'e.

Figure 1

The input voltage appears across the emitter diode.

Hence emitter current i_e = V_in / r'_e.

Since, collector current approximately equals emitter current and i_C  = i_e and v_out = - i_e R_C  (The minus sign is used here to indicate phase the inversion)

Further vout = - (V_in R_C) / r'_e

Therefore voltage gain A = v_out / v_in = -R_C / r'_e

The AC source driving an amplifier has to supply alternating current to amplifier. The input impedance of the amplifier determines how much current the amplifier takes from the AC source.

In the normal frequency range of an amplifier, where all the capacitors look like AC shorts and other reactance are negligible, the AC input impedance can be defined as

z_in= v_in/ i_in

Here v_in, i_in are peak to peak values or RMS values

The impedance looking directly into the base can be symbolized z_in (base) and can be given by

Z _in(base) = v_in / i_b ,

Since,v _in = i_e r'_e

» b_i b r'_e

z_in (base) = b r'_e.

From AC equivalent circuit, the input impedance z_in is parallel combination of R₁ , R₂ and b r'_e.

Z_in = R₁ || R₂ || b r'_e

The Thevenin voltage appearing at the output is

v_out = A v_in

The Thevenin impedance is parallel combination of the R_C and internal impedance of the current source. The collector current source is the ideal source; thus it has an infinite internal impedance.

z_out = R_C.

Simplified AC equivalent circuit is shown in the figure 2.

Figure 2

Email based Electronics Devices and circuits assignment help - homework help at Expertsmind

Are you searching Electronics Engineering assignment help expert for help with Voltage gain questions?  Voltage gain topic is not easier to learn without any external help?  We at www.expertsmind.com offers free lecture notes for Electronics Devices and circuits assignment help and Electronics Devices and circuits homework help. Live tutors are available 24x7 hours for helping students in their Voltage gain related problems. We provide step by step Voltage gain question's answers with 100% plagiarism free content. We prepare quality content and notes for Voltage gain topic under Electronics Devices and circuits theory and study material. These are avail for subscribed users and they can get advantages anytime.

Why Expertsmind for assignment help

1. Higher degree holder and experienced experts network
2. Punctuality and responsibility of work
3. Quality solution with 100% plagiarism free answers
4. Time on Delivery
5. Privacy of information and details
6. Excellence in solving electronics engineering questions in excels and word format.
7. Best tutoring assistance 24x7 hours