Question 22.6: Estimate the f3dB of the diff-amp in Ex. 22.5 if it drives a......
Estimate the f_{3dB} of the diff-amp in Ex. 22.5 if it drives a load capacitance of 1 pF. Verify your hand calculations with SPICE.
Step-by-Step
The resistance on the output node is r_{o2}||r_{o4}=111\,k\Omega; therefore, since this is the high-impedance node, we can estimate the circuit’s 3-dB frequency in the circuit as
f_{3d B}=\frac{1}{2\pi\cdot 111k\cdot1\ p F}=1.4\ M H zThe simulation results are seen in Fig. 22.14.
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