Control circuitry for quartz crystal deposition monitor
First Claim
1. Monitoring circuit for monitoring at least one resonant frequency of a piezoelectric crystal on which a film of material is being vacuum deposited to control a source of vapors of said material;
- the monitoring circuit comprising;
a) controllable frequency generating means for generating a drive signal at a frequency, independent of the crystal resonance frequency, selected within a band of RF frequencies that includes the at least one resonant frequency of said piezoelectric crystal;
b) a duplexing circuit having an input coupled to said frequency generating means to receive said drive signal therefrom, a crystal terminal coupled to said crystal and supplying the drive signal to said crystal and receiving a response signal reflected back from the crystal, and an output terminal at which said response signal appears, the response signal having the frequency of said drive signal but a phase that depends on the proximity of the drive signal frequency to a resonant frequency of said crystal;
c) phase detector means supplied with said drive signal and said response signal and having a phase output signal whose value indicates the relative phase of the drive and response signals, from a negative level through zero to a positive level; and
d) controller means coupled to said frequency generating means and said phase detector means for controllably changing the frequency of said drive signal and monitoring the frequency at which said phase detector signal indicates a zero level to identify the frequency of each of said one or more resonances.
2 Assignments
0 Petitions
Accused Products
Abstract
A monitoring circuit monitors a piezoelectric crystal for changes in its resonant frequency as a film of material is vacuum deposited on it, e.g. to control a source of vapors of the material. A controllable frequency generator generates a drive signal of a accurately known frequency and phase within a band of RF frequencies that includes the resonant frequency of the crystal. The RF signal is applied through a duplexing circuit to the crystal, and a response signal is applied through the duplexing circuit to a signal amplifier and limiter circuit to a phase detector. The phase detector is also supplied with the RF drive signal, and has a phase output signal which is zero when the crystal is at resonance, and is negative or positive when the applied RF signal is below or above resonance, respectively. A micro-controller can be employed for controllably sweeping the frequency of the drive signal and then monitoring the frequencies at which the phase detector signal indicates zero, to identify the frequency of each of the one or more resonances. A cable compensation control circuit can also be coupled to the duplexing circuit for balancing the reactance of the conductive paths associated with the crystal. This can include a voltage controlled capacitance and a portion of a transformer within the duplexing circuit.
46 Citations
7 Claims
-
1. Monitoring circuit for monitoring at least one resonant frequency of a piezoelectric crystal on which a film of material is being vacuum deposited to control a source of vapors of said material;
- the monitoring circuit comprising;
a) controllable frequency generating means for generating a drive signal at a frequency, independent of the crystal resonance frequency, selected within a band of RF frequencies that includes the at least one resonant frequency of said piezoelectric crystal; b) a duplexing circuit having an input coupled to said frequency generating means to receive said drive signal therefrom, a crystal terminal coupled to said crystal and supplying the drive signal to said crystal and receiving a response signal reflected back from the crystal, and an output terminal at which said response signal appears, the response signal having the frequency of said drive signal but a phase that depends on the proximity of the drive signal frequency to a resonant frequency of said crystal; c) phase detector means supplied with said drive signal and said response signal and having a phase output signal whose value indicates the relative phase of the drive and response signals, from a negative level through zero to a positive level; and d) controller means coupled to said frequency generating means and said phase detector means for controllably changing the frequency of said drive signal and monitoring the frequency at which said phase detector signal indicates a zero level to identify the frequency of each of said one or more resonances. - View Dependent Claims (2, 3, 4, 5, 6, 7)
- the monitoring circuit comprising;
Specification