Q.Draw the circuit diagram of crystal oscillator. Draw the electrical equivalent circuit of a crystal.

A crystal oscillator uses a piezoelectric quartz crystal as the frequency-determining element in the feedback path of a transistor amplifier; the crystal's AC equivalent is a series R–L–$C_s$ branch in parallel with the mounting capacitance $C_m$. …

[!TLDR]

A crystal oscillator is a transistor oscillator whose tank is replaced by a quartz crystal; the crystal behaves electrically as a series R–L–$C_s$ branch in parallel with a mounting capacitance $C_m$, fixing the frequency at $f_s = \dfrac{1}{2\pi\sqrt{LC_s}}$.

In the BJT crystal oscillator (Figure 6.4.4), $R_1$, $R_2$ and $R_E$ provide the DC bias, $C_E$ is the bypass capacitor and $C_C$ the coupling capacitor, and RFC is the radio-frequency choke that isolates the DC supply from the collector oscillations. The crystal is connected as a series element in the feedback path from the collector to the base and is excited in its series-resonant mode; a capacitive voltage divider $C_1$–$C_2$ completes the feedback. The transistor gives $180^\circ$ and the capacitor divider a further $180^\circ$, so the total loop phase shift is $360^\circ$.

The AC electrical equivalent circuit of the crystal (Figure 6.4.2) has two parallel branches between the two terminals: a series branch consisting of a resistance R, an inductance L and a capacitance $C_s$ (L represents the crystal's mass, $C_s$ its elasticity and R its mechanical friction), and, in parallel with this branch, the mounting capacitance $C_m$ (formed by the two metal electrodes with the crystal slab as dielectric). …