Capacitor trimming system in a quartz-crystal oscillator

A trimming system for a quartz-crystal oscillator comprising:

• (a) an oscillation circuit including a quartz-crystal piece, a trimmer capacitor coupled to said quartz-crystal piece for adjusting the oscillating frequency of the quartz-crystal piece, and a semiconductor electronic circuit coupled to said quartz-crystal piece for operating said quartz-crystal piece;
• (b) said trimmer capacitor having at least a fixed outer trimming electrode, a common inner electrode fixed parallel to said trimming electrode and dielectric body sandwiched between said two electrodes, at least said trimming electrode being exposed for enabling the trimming of the area of the trimming electrode, said trimming electrode having a coarse adjustment portion parallel and aligned with said common electrode and a fine adjustment portion positioned in the same plane as the coarse adjustment portion but outside of said common electrode,
• (c) a signal detector coupled acoustically with said quartz-crystal piece for providing an electrical signal relating to the oscillation of said quartz-crystal piece,
• (d) a counter means connected to the output of said signal detector through an amplifier for measuring the oscillating frequency of said quartz-crystal piece,
• (e) a reference frequency oscillator for providing the desired reference frequency,
• (f) a comparator coupled to said counter and said reference frequency oscillator, for comparing the frequency of said quartz-crystal oscillator measured by said counter means with the output frequency of said reference frequency oscillator,
• (g) a trimming unit operably coupled to said trimmer capacitor, for trimming the area of said trimming electrode of said trimmer capacitor,
• (h) a memory means coupled to said counter means for storing the frequency f.sub.1 measured by said counter means in the preceding trimming step,
• (i) a calculation means coupled to said memory means, for providing the difference f.sub.3 between the twice (2f.sub.2) of the frequency measured by said counter means at the present step and the output (f.sub.1) of said memory means,
• (j) a second comparator coupled to said calculation means and said reference frequency oscillator, for comparing the output (f.sub.3) of said calculation means with the output frequency (f.sub.0) of the reference frequency oscillator, and providing a trigger signal when f.sub.3 is equal to or larger than f.sub.0, and
• (k) a trimming unit control operably coupled to said trimming unit, for controlling the operation of said trimming unit according to the output of said comparator, said trimming unit control being arranged to control the trimming unit so that the coarse adjustment portion of said trimming electrode is initially trimmed and when said second comparator provides the trigger signal thereto, the fine adjustment portion of said trimming electrode is trimmed until the oscillation frequency of said quartz-crystal piece reaches the reference frequency.