Self-Loaded Ring Oscillator
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
Ring oscillators are used for process monitor applications and as indicators of technology performance. Typically, a loop of an odd-number (N) of NAND or NOR gates is used, the period (T) of oscillation observed, and the average stage delay calculated from the equation: td = T/2N. The self-loaded ring oscillator increases sensitivity to various performance-related parameters and requires less layout area. The figure shows a particular configuration of the self-loaded ring oscillator utilizing five stages (a, b, c, d, e). This configuration of fan-in = fan-out = 3 NANDs (or NORs) can be extended to any odd-number, depending on the stage delay to be resolved. Additional node capacitance can be added. The concept of forward fan-out can also be extended to include more inputs.