Differential Amplifier

*It is used as entry stage in the most of operational amplifiers; *It eliminates the need for bypass capacitors; *That is composed by 2 stages common emitter amplifiers in parallel with a common emitter resistor; *There is no lower cutoff frequency; *Vout is defined as: Vout = VC2 - VC1; *When V1 > V2: Vout > 0; *When V1 < V2: Vout < 0; *The output voltage equation is: Vout = Av(V1 - V2) Av is the voltage gain V1 is non-inverting input V2 is inverting input *When V2 = 0: Vout = Av(V1); *When V1 = 0: Vout = -Av(V2); *The voltage gain is defined as: Av = (RC/r'e) RC is the collector resistor value (RC=RC1=RC2) r'e = 25mV/IE (B-E junction resistance)