A Differential Two-Pin Crystal Oscillator—Concept, Analysis, and Implementation

This brief presents the concept, analysis, design, and measurement results of a differential integrated crystal oscillator (XTO). The XTO requires only two package pins and is connected parallel to the crystal and to the load capacitor, but the amount of negative oscillator resistance RoscRoscis defined as the negative real part of the impedance (Z2 in Fig. 1) seen by the series resonance circuit inside the crystal: Rosc=-Re(Z2). is similar to that of three-pin XTOs such as Pierce or Colpitts. The basic idea is to use three small integrated capacitors and two differential transconductance stages to construct an impedance similar to that of Pierce or Colpitts XTOs