The two oscillator circuits under are well suited for utilizing crystal oscillators in series or parallel method: Significant-repetition-fee and high-electrical power picosecond regenerative amplifier dependant on just one bulk Nd:GdVO4 crystal A timing reference incorporating only one-crystal-silicon micromechanical resonator with a quality issue of larger sized than one million plus https://www.hxcrystals.com/seokeywords/bulk-crystal-oscillator.html