bias of a transistor
M5 is the DC_bias feedback element, with the FET used as a non-linear resistor.

The full oscillator circuit looks something like this







simulate this circuit &ndash; Schematic created using CircuitLab

Given a 1MegOhm resistor is HUGE, the designer choses a low W/L (1/10 or 1/100) ratio MOSFET, possibly a PFET inside a well to provide a cleaner environment for the PFET and thus create a lower-jitter operating point.