3EJ4- Lab 1_Quraiz2

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Electronic Devices and Circuits II – 3EJ4 Lab #1 - Device Characterization and Biasing Circuits Zuhaib Quraishi - Quraiz2 – 400306494 Date Submitted :22/09/2023

Part 1: DC Characterization of an NPN-BJT 2N3904 Q1. (7 Points) Based on the simulated data in Steps 1.2-1.4, use the bias condition giving the closest IC value to the desired collector current, find out: (Line 72 on Excel file Sheet: “Steps 1.2-1.4”) (1) What are the simulated VBEon in volts and the base current IB in μA? VBEon : 0.621V IB = 8.79 μA (2) What is the β = IC/IB value at this IC? β = 1030 / 8.79 β = 117 (3) What is the early voltage |VA| in volts? y=1E-06x + 0.001 |VA| = the x-intercept of the line 0=1E-06x + 0.001 x = |VA| = 1000 V (4) What is the output resistance r o in kΩ? Output resistance (ro) = 976 kΩ (5) What is the transconductance g m in mS? Transconductance (gm) = 41.0 mS (6) What is the input resistance rπ in kΩ? Input resistance (rπ) = 2.845 kΩ Q2. (8 Points) Based on the measured data in Step 1.8, use the same bias condition found in Q1 (or the first reliable data if that bias condition is an outlier), find out: (Line 72 on Excel file Sheet: “Steps 1.8”) (1) How much is the measured collector current IC in mA? IC = 1.70 mA (2) What are the measured V BEon in volts and the base current IB in μA? VBEon : 0.673V IB = 8.27 μA (3) What is the β = IC/IB value at this IC? β = 1700 / 8.27 β = 206 (4) What is the early voltage |VA| in volts? |VA| = 170 V

(5) What is the output resistance r o in kΩ? Output resistance (ro) = 100 kΩ (6) What is the transconductance gm in mS? Transconductance (gm) = 68.0mS (7) What is the input resistance rπ in kΩ? Input resistance (rπ) = 3.024 kΩ Part 2: DC Characterization of a PNP-BJT 2N3906 Q3. (7 Points) Based on the simulated data in Steps 2.2-2.4, use the bias condition giving the closest IC value to the desired collector current, find out: (Line 81 on Excel file Sheet: “Steps 2.2-2.4”) (1) What are the simulated V EBon in volts and the base current IB in μA? VBEon : 0.660V IB = 8.4 μA (2) What is the β = IC/IB value at this IC? β = 123 (3) What is the early voltage |VA| in volts? |VA| = 143 V (4) What is the output resistance r o in kΩ? ro = 139 kΩ (5) What is the transconductance g m in mS? gm = 41.2mS (6) What is the input resistance rπ in kΩ? rπ = 2.976 kΩ Q4. (8 Points) Based on the measured data in Step 2.8, use the same bias condition found in Q3 (or the first reliable data if that bias condition is an outlier), find out: (Line 81 on Excel file Sheet: “Steps 2.8”) (1) How much is the measured collector current IC in mA? IC = 1.99mA (2) What are the measured V EBon in volts and the base current IB in μA? VBEon : 0.681V IB = 8.19 μA

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(3) What is the β = IC/IB value at this IC? β = 243 (4) What is the early voltage |VA| in volts? |VA| = 27 (5) What is the output resistance r o in kΩ? ro = 13.6kΩ (6) What is the transconductance gm in mS? gm = 79.6 mS (7) What is the input resistance rπ in kΩ? rπ = 3.053 kΩ Part 3: Design of a Current Source/Sink Q5. (10 Points) Express the base current IB as a function of VBB, RBB, VBEon, R3 , VEE, and β.

Q6. (10 Points) Comparing the IB expressions obtained in Q5 and in (3), what is the difference between these two equations? For a change ∆VEE in the power supply V EE, derive equations for the resulting change in the base current ∆IB using the IB expressions obtained in Q5 and in (3). Show that the emitter resistor R3 reduces the change in the base current ∆IB as a result of the change ∆VEE in the power supply VEE. The obtained equation in Q5 and the given equation (3) in the lab report are very similar. However, the derived expression has an additional term in the denominator of R3(β + 1). This difference is due to the difference in the R3 value. In the lab report, R3 is set to zero, eliminating that term, but in Q5, R3 displays the behaviour of a feedback resistor. This causes a change in the voltage values as there is a drop across R3, and VE no longer equals VEE.

Q7. (15 Points) Inserting the feedback R3 at the emitter of the BJT not only stabilizes the IB but also improves (or increases) the output resistance Ro of the current sink shown in Fig. 6/Fig. 7 (i.e., I o is Page 12 more stable when there is a change in VCE). Using a π- model for the BJT, prove that the output resistance of the current sink is:

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Q8. (10 Points) Inserting the feedback R3 at the emitter of the BJT improves the stabilization of the Q- point at the cost of increased Vo, min. What is the Vo, min of the constant current sink when R3 ≠ 0? Q9. (15 Points) For VEE = -5V, if we want to design a current sink with Io = 1.0 mA and Vo, min = -2 V using the NPN-BJT 2N3094 characterized in Q1, what is the resistance value for R3? To reduce the DC power consumption of R1 and R2, we usually choose large resistance values (in tens or hundreds of kΩ) for R1 and R2. Suppose we choose R2 = 100 kΩ, calculate R1 in kΩ. Verify the Io vs. VCC characteristics of the design by sweeping VCC from -5V to 5V with a 0.05V step and post the waveform of the simulated Io vs. VCC characteristics using the command “Window -> Copy to Clipboard” in the PSpice simulator window.

The collector current (IC) increases as the VCC increases. This IC value increases until it plateaus at approximately 1mA at a VCC value of -2V.

Q10. (10 Points) When designing the constant current sink shown in Fig. 6, we assume that |VCE| ≥ 0.3V and Q1 works in the active region. Based on the resistance values obtained in Q9, sweep VCC in Fig. 6 from -5 V to +5 V with a 0.05 V step and measure VE and IC to determine the |VCE| required for Q1 to work in the active region.

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