The 2 oscillator circuits below are appropriate for making use of crystal oscillators in series or parallel manner: Large-repetition-price and high-ability picosecond regenerative amplifier determined by just one bulk Nd:GdVO4 crystal A timing reference incorporating only one-crystal-silicon micromechanical resonator with a high quality component of bigger than one million in https://www.hxcrystals.com/seokeywords/bulk-crystal-oscillator.html