Experiment 8 Notes V2 18 R1 365.4uA 40k Rsig 50 C1 Q2N2222A 5.373mA C2 10uF 0A VOFF = 0.00000001 V3 VAMPL = 2.5 FREQ = 10kHz 0A 05.738mA Q1 26.87uA 10uF -5.400mA Re 5.400mA 500 V R2 338.5uA 10k Rl V 5k 0A 0 3.0V 2.0V 1.0V -0.0V -1.0V -2.0V -3.0V 0s V(V3:+) 20us V(Rl:2) 40us 60us 80us 100us Time Vin = 2.499 V (Calculated) Vout = 2.462 V (Calculated) Av = 0.9849 V/V (Calculated) 120us 140us 160us 180us 200us Ic = 5.4 mA (Calculated) Since this amplifier is a common collector, the gain is 1. This circuit is also known as a unity gain amp, or a buffer amp. The values we calculated result in a design that meets the required specifications. The gain is 9.8, which is greater than the required 9.5. Output swing across load is driven to 2.4 V which is greater than the 2 V required in the specifications. Part 4 – Output Swing Clipping Limit 3.0V 2.0V 1.0V -0.0V -1.0V -2.0V -3.0V 0s V(V3:+) 20us V(Rl:2) 40us 60us 80us 100us 120us 140us 160us 180us 200us Time Clipping occurs around 2.5 V when the input is at 2.7 V as shown in Figure (INSERT FIGURE HERE). (Calculated) We used PSPICE to measure the output voltage at which our Vout begins to show distortion, meaning the maximum voltage our amplifier is able to drive the output. In both our experimental and PSPICE circuits, we were able to drive the load resistor to around 2.7V. This surpasses the specified output swing of at least 2V across a 5kOhm load resistance. Part 5 – Input Impedance V2 18 R1 40k Rsig 0 Q1 C1 Q2N2222A 7.5k 10uF C2 V VOFF = 0.00000001 V3 VAMPL = 2 FREQ = 10kHz 10uF V R2 10k Re 500 Rl V 5k 0 2.0V 1.0V 0V -1.0V -2.0V 0s V(V3:+) 20us V(Rl:2) 40us V(C1:1) 60us 80us 100us Time Resistor inserted = 7.5k (PSPICE) Input Voltage = 2 V (PSPICE) Resistor Voltage = 1 V (PSPICE) Input Impedance Calculated = 7.5 kOhms (PSPICE) 120us 140us 160us 180us 200us In experiment 6, we learned that we could essentially guess and check with various input resistors to find out what the input impedance of our circuit was. This was done by inserting an additional input resistor (Rn) with a value such that our Vn will be half the input voltage (Vin) of the original circuit. We know this because whenever a voltage is passed through 2 equivalent resistors in series, the voltage is divided in half. In Figure (INSERT FIGURE HERE), we see that our original PSPICE input voltage is 1.99V, and when a 7.5kΩ resistor is inserted, the voltage across that resistor becomes 0.99V. Therefore we can conclude that our input impedance (Zin) is approximately 7.5kΩ. This coincides with the generalization that common collector amplifiers have high input impedance, which explains why they are commonly used as the last stage in multi-stage amplifiers. Part 6 – Output Impedance V2 18 R1 40k Rsig 0 Q1 C1 Q2N2222A 500 VOFF = 0.00000001 V3 VAMPL = 100mV FREQ = 10kHz 10uF C2 10uF V V R2 10k Re 500 Rl 10 0 100mV 50mV 0V -50mV -100mV 0s V(V3:+) 20us V(Rl:2) 40us 60us 80us 100us 120us 140us 160us 180us Time Vin = 100mV (PSPICE) Open circuit Vout = 98mV (PSPICE) Resistor Inserted = 10 Ohms (PSPICE) New Vout = 50 mV (PSPICE) Output Impedance = 10 Ohms (PSPICE) As with finding input impedance, we use a similar guess and check method to find output impedance. This is done by first measuring the output voltage with an open (infinite) load 200us resistance. In PSPICE, this is done by inserting a load resistance of < 1 MegaOhm, since pspice doesn’t handle open circuits. Next, we increase the original load resistance such that the output voltage (open load) is divided in half. Above in Figure (INSERT FIGURE HERE), we can see that inserting a 10Ω resistor changes our output voltage from 98mV to 50mV. Therefore our output impedance (Zout) is approximately 10Ω.