The two oscillator circuits down below are appropriate for applying crystal oscillators in sequence or parallel manner: Substantial-repetition-rate and large-ability picosecond regenerative amplifier according to one bulk Nd:GdVO4 crystal A timing reference incorporating only one-crystal-silicon micromechanical resonator with a high quality issue of larger sized than one million as well https://www.hxcrystals.com/seokeywords/bulk-crystal-oscillator.html