The two stages differ only in gate-drain capacitance: the second model deliberately has much larger CGDO/Cgd.
For an inverting gain Av, the input contribution of Cgd is approximately Cgd*(1-Av). With Av near -7.8, even a few picofarads can look like tens of picofarads at the input. Combined with 10 kOhm source resistance this creates a real bandwidth limit.
Plot D1 and D2 over frequency. The high-Cgd model should roll off earlier. This is the MOS version of the BJT Cmu Miller effect introduced in Chapter 03.
