A ring oscillator working in the GHz range is divided to give an observable output frequency in the 20 MHz range.
Top-Level Complete Mixed-Signal Functionality Verification in Verilog
PEX Sims Verifying Performance
A supply current of 1-2 mA when enable is high indicates that the ring oscillator is functional. The final output can be observed in the 20 MHz range. Test/debug mode verifies the divider functionality at low frequency. The ring oscillator can be disabled by on-chip signals (ena = low).
Oscilloscope (100 MHz), power supply, function generator (10 MHz, digital).