A 48-MHz Differential Crystal Oscillator With 168-fs Jitter in 28-nm CMOS

A 168-fs rms jitter, 48-MHz differential crystal oscillator based on a new active inductor biasing circuit achieves differential operation with low noise, power, and area overhead. This architecture has two significant advantages compared to the single-ended crystal oscillators that are normally used: 1) this circuit rejects power supply noise and interference which leads to lower jitter and 2) the crystal oscillator-induced spurious tones are smaller and therefore less detrimental to sensitive blocks (e.g., LNA) in RF radios. This paper theoretically analyzes the differential crystal oscillator and provides detailed design considerations. A prototype requires half the power and 80% less area than previously reported differential crystal oscillators. Implemented in a 28-nm LP CMOS process, it draws 1.5 mA from a 1-V supply and occupies 0.013 mm2.