Govt. Exams
Entrance Exams
For non-inverting amplifier: Acl = 1 + (Rf/Rin) = 1 + (90/10) = 1 + 9 = 10
Voltage gain Av = -gm × Rc, where gm is transconductance and Rc is collector resistance. Increasing Rc directly increases voltage gain.
Ideal op-amp assumptions include infinite input impedance (no current drawn at inputs), zero output impedance, and infinite open-loop gain.
LM741 has a GBW product of approximately 1 MHz, which is why it's limited to low-frequency applications. Modern op-amps have higher GBW.
Time constant τ = RC = 10×10³ × 100×10⁻⁹ = 10×10⁻⁴ = 1×10⁻³ s = 1 ms.
In the active region, IC = β × IB where β is the DC current gain (typically 50-300 for silicon BJTs).
The voltage gain of a voltage follower is Av ≈ 1 (or slightly less due to emitter resistance effects). It is used for impedance matching.
CMRR (dB) = 20 log(CMRR linear). Therefore, 80 = 20 log(CMRR), giving CMRR = 10^4 = 10,000.
The input impedance of a CE amplifier is Zin ≈ β × re, where β is current gain and re is emitter resistance (≈ VT/IE).
In saturation, the transistor acts almost like a closed switch with minimal voltage drop across it, resulting in very low output impedance.
