Using a computer simulation, verify the results of Example 10.9 (Textbook). V+ II. EXAMPLE 10.9 Objective: Compare the o

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Using A Computer Simulation Verify The Results Of Example 10 9 Textbook V Ii Example 10 9 Objective Compare The O 1 (118.65 KiB) Viewed 57 times

Using a computer simulation, verify the results of Example 10.9 (Textbook). V+ II. EXAMPLE 10.9 Objective: Compare the output resistance of the cascode MOSFET current source to that of the two-transistor current source. Consider the two-transistor current source in Figure 10.17 and the cascode current source in Figure 10.18. Assume IREF = 10 = 100 μA in both circuits, λ = 0.01 V-1 for all transistors, and gm = 0.5 mA/V. Solution: The output resistance of the two-transistor current source is, from Equa- tion (10.48(b)), 1 1 To = =1MΩ λ/REF (0.01) (0.10) For the cascode circuit, we have ro2 = 104 = 1 MS. Therefore, the output resistance of the cascode circuit is, from Equation (10.57), R₁ = 104 +102(1 + 8m³04) = 1 + (1)[1 + (0.5 × 10-³)(10%)] or R = 502 ΜΩ Comment: The output resistance of the cascode current source is substantially larger than that of the basic two-transistor circuit. Since dlo ∞ 1/R₁, the load current in the cascode circuit is more stable against variations in output voltage. Design Pointer: Achieving the output resistance of 502 M$ assumes the transistors are ideal. In fact, small leakage currents will begin to be a factor in actual output resistance values, so a value of 502 MS2 may not be achieved in reality. REF M3 M₁ VGS3 M₂ VGSI ID2 = 10 + VGS2 V- Figure 10.17 MOSFET current source