Lab 2-A: Bias Stability

Your task is to study the effect that transistor parameters have obtaining a robust circuit design. A robust circuit design is relatively not sensitive to the specific value of transistor parameters, especially the ones which vary widely (like β, I_S, and variations with temperature).

This study includes circuit analysis and examining the mathematical properties of the resulting equations, and building example circuits and measuring how the resulting bias conditions change when replacing the transistor.

Obtain 10 NPN transistors of the same model (2N3904). Use the LCR-T4 semiconductor + LCR tester to measure each transistor’s forward β_F and the V_BE at the measurement conditions. Use small pliers to handle the transistors to avoid heating them with your fingers in order to make the measurements more consistent. Remember that, for example, V_BE changes by -2 mV / °C.

Use the tester’s short manual LCR-T4_semiconductor-tester_short.pdf on Google Drive to help compute the base current for each transistor under the measurement conditions. Note: the voltage between the + and - nodes is set to 5.0 V by a voltage regulator and the two low-value resistors are 680 Ω instead of the 700 Ω in Figure 1.1 (a) and (b).

Use this Google Sheet to record your data. Each group should use a different 100’s position digit for the transistor IDs (the N in the integer Nxx).