M1 in the shown circuit is saturated with $g_m=0.01$ S. Ignore internal parasitic capacitances and set channel-length modulation to zero. The small-signal input pole frequency in kHz is ________.
The low-frequency common-source gain is $-g_mR_D=-10$. Miller multiplication makes the input capacitance approximately $50(1-(-10))=550$ pF. With 5 kΩ source resistance this gives $f_p\approx1/[2\pi(5000)(550\mathrm{\ pF})]=57.87$ kHz.
An exact two-node calculation with the sole feedback capacitor gives time constant $C(R_S+R_D+g_mR_SR_D)=2.8$ μs, or **56.84 kHz**. Both agree with the official interval 56–63 kHz; the latter includes the output-node loading exactly.
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