A Simple Operational Amplifier ** Circuit Description ** * power supplies Vcc 4 0 DC +15V Vee 5 0 DC -15V * differential-mode signal level Vd 101 0 DC 0V Rd 101 0 1 EV+ 1 100 101 0 +0.5 EV- 2 100 101 0 -0.5 * common-mode signal level Vcm 100 0 DC 0V * 1st stage R1 4 7 20k R2 4 8 20k Q1 7 1 6 npn_transistor Q2 8 2 6 npn_transistor Q3 6 9 5 npn_transistor * 2nd stage R3 4 11 3k Q4 4 7 10 npn_transistor Q5 11 8 10 npn_transistor Q6 10 9 5 npn_transistor 4 * 3rd or output stage R4 4 12 2.3k Q7 13 11 12 pnp_transistor R5 13 5 15.7k Q8 4 13 3 npn_transistor R6 3 5 3k * biasing stage Rb 0 9 28.6k Q9 9 9 5 npn_transistor * transistor model statements .model npn_transistor npn ( Is=18fA Bf=100 VAf=100V ) .model pnp_transistor pnp ( Is=18fA Bf=100 VAf=100V ) ** Analysis Requests ** * compute DC operating point using the following initial guesses .OP .NODESET V(3)=0V V(6)=-0.7V V(7)=+10V V(8)=+10V V(9)=-14.3V V(10)=+9.3V + V(11)=+12V V(12)=+12.7V V(13)=+0.7V * compute large-signal differential-input transfer characteristics of amplifier .DC Vd -15V +15V 100mV ** Output Requests ** .PLOT DC V(3) .probe .end