Abstract:
The unique properties of a monolithic crystal filter are turned to account in a low-frequency crystal oscillator system. Each of two different relatively high-frequency signals is generated by a respective crystal controlled oscillator. The oscillators share a common crystal wafer to which each is connected by a respective pair of electrodes. The relatively low beat frequency signal or difference frequency of the oscillators is extracted by a third set of electrodes mounted on the crystal between the electrode pairs connected to the oscillators.
Abstract:
Three or more resonator-forming electrode pairs and a crystal wafer on which they are mounted, form a multiresonator crystal filter with respective inductors connected to two of the pairs. The electrode pairs have masses such as to tune the frequency exhibited by the unconnected resonator to a frequency fp. The inductors tune the interelectrode capacitances of the connected resonators to the frequency fp. The masses of electrodes in the connected resonators tune the mechanical resonance of the crystal between the electrodes to the frequency fp. The electrode spacings in view of their masses are such as to achieve predetermined couplings between resonators.
Abstract:
Multiresonator monolithic crystal structures are coupled to each other at predetermined coupling coefficients K by means of coupling capacitors that shunt the respective structure''s resonators to be coupled. The total capacitance coupling the resonators has a value CC C1/K where C1 is the equivalent motional capacitance of the resonators. The capacitor-coupled resonators, when uncoupled, exhibit frequencies f0 1-K, where f0 is the filter''s midband frequency.