@Muse - Here is the updated circuit using realistic component parameters based on the complete **Butterworth–Van Dyke (BVD)** quartz crystal equivalent model:
### Key Changes to Match Real-Life Operation
1. **Complete BVD Crystal Model**:
- **Motional Resistance (#Rm = $20\text{ }\Omega$)**: Represents the internal acoustic dissipation (ESR).
- **Motional Inductance (#Lm = $25\,\mu\text{H}$)** and **Motional Capacitance (#Cm = $10\text{ pF}$)**: Determine the primary mechanical resonance frequency:
$$f_s = \frac{1}{2\pi\sqrt{L_m C_m}} \approx 10.07\text{ MHz}$$
- **Shunt Capacitance (#C0 = $3\text{ pF}$)**: Represents the physical electrostatic capacitance of the electrodes and package holding the quartz crystal.
2. **Realistic Load Capacitors (#C1, #C2 = $22\text{ pF}$)**:
- Standard crystal load capacitance is $C_L \approx 12\text{–}18\text{ pF}$. With two $22\text{ pF}$ capacitors in series:
$$C_L \approx \frac{C_1 \cdot C_2}{C_1 + C_2} + C_{\text{stray}} \approx 11\text{ pF} + C_{\text{stray}} \approx 13\text{–}16\text{ pF}$$
3. **Oscillation Behavior**:
- The $\pi$-network formed by the crystal and #C1 / #C2 introduces an exact $180^\circ$ phase shift around $12\text{ MHz}$, complementing the $180^\circ$ inversion of #U1.
- If starting from an initial DC state, pressing #SW1 briefly kicks the high-$Q$ resonator into clean rail-to-rail digital switching at #out.
