Ring oscillators using invertors and diff amp

Hi,


Can anyone tell me the difference between the ring oscillators using odd number of invertors and ring oscillator built using differentiel amplifiers.


Which one is better in what circumstances.

Thanks in advance.

Prakash.

Technically speaking, it is easier to match the aspect ratio of PMOS and NMOS in CMOS inverters used in ring oscillator. Matching aspect ratio is necessary to make sure the rise time and fall time is correct. Matching aspect ratio in a differential amplifier is an entirely different level of difficulty because you also have to tune the differential current.

For digital circuits, ring oscillator using CMOS inverters are used because of CMOS inverter is ratioless and it benefits from device scaling. It drives capacitive load that is good for low-power but medium-speed application.

For RF-analog, diff amp based ring oscillator is used but less common these days because of the shift in current trend moving towards low-power and ultra-low power.