The 2 oscillator circuits below are appropriate for using crystal oscillators in sequence or parallel mode: Significant-repetition-rate and substantial-ability picosecond regenerative amplifier depending on one bulk Nd:GdVO4 crystal A timing reference incorporating a single-crystal-silicon micromechanical resonator with a high quality component of larger sized than one million plus a ... https://www.hxcrystals.com/seokeywords/bulk-crystal-oscillator.html