Low Phase Noise RF Oscillators Based on Thin-Film Lithium Niobate Acoustic Delay Lines

Abstract

An RF oscillator has been demonstrated using a wideband SH₀ mode lithium niobate acoustic delay line (ADL). The design space of the ADL-based oscillators is theoretically investigated using the classical linear time-invariant (LTI) phase noise model. The analysis reveals that the key to low phase noise is low insertion loss (IL), large delay (τ_G), and high carrier frequency ( f_o). Two SH₀ ADL oscillators based on a single SH₀ ADL ( f_o = 157 MHz, IL = 3.2 dB, τ_G = 270ns) but with different loop amplifiers have been measured, showing low phase noise of -114 dBc/Hz and -127 dBc/Hz at 10-kHz offset with a carrier power level of -8 dBm and 0.5 dBm, respectively. These oscillators not only have surpassed other Lamb wave delay oscillators but also compete favorably with surface acoustic wave (SAW) delay line oscillators in performance. [2019-0223].