Surface electric potential sensor drive and induction noise cancellation circuit
First Claim
1. A surface potential sensor, comprising:
- a chopper portion for cutting electric lines of force radiated from a component to be measured, said chopper portion cutting the electric lines of force at a know frequency;
a detection electrode for detecting said cut electric lines of force and for outputting an A.C. voltage signal;
a pre-amplifier circuit connected to said detection electrode for amplifying the A.C. voltage signal and outputting an amplified A.C. voltage signal;
a drive circuit for applying a drive signal to a drive electrode of said chopper portion to oscillate said chopper portion; and
induction noise removing means for removing induction noise imparted by the drive signal from the amplified A.C. signal, said induction noise removing means comprising a differential amplifier circuit for amplifying a difference between the amplified A.C. voltage signal and the drive signal, and outputting an amplified difference signal.
1 Assignment
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Accused Products
Abstract
Surface potential is detected with high precision by removing induction noise generated by a drive circuit and transmitted to a detection electrode. Induction noise imparted by a drive circuit to an A.C. voltage signal is cancelled out by supplying an output of a pre-amplifier for amplifying the A.C. voltage signal derived from a detection electrode and an output of the drive circuit for applying a drive signal to a chopper portion to a differential amplifier and differentially amplifying them. Particularly, an attenuator for making a level of the amplified A.C. voltage signal substantially coincident with a level of a signal from the drive circuit and an inverter/amplifier for making phase deviation coincident are provided in an output portion of the pre-amplifier circuit.
17 Citations
16 Claims
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1. A surface potential sensor, comprising:
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a chopper portion for cutting electric lines of force radiated from a component to be measured, said chopper portion cutting the electric lines of force at a know frequency; a detection electrode for detecting said cut electric lines of force and for outputting an A.C. voltage signal; a pre-amplifier circuit connected to said detection electrode for amplifying the A.C. voltage signal and outputting an amplified A.C. voltage signal; a drive circuit for applying a drive signal to a drive electrode of said chopper portion to oscillate said chopper portion; and induction noise removing means for removing induction noise imparted by the drive signal from the amplified A.C. signal, said induction noise removing means comprising a differential amplifier circuit for amplifying a difference between the amplified A.C. voltage signal and the drive signal, and outputting an amplified difference signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A surface potential sensor, comprising:
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a detection electrode for receiving electric lines of force emitted from a component to be measured and outputting an A.C. voltage signal; a reed vibrator connected to said detection electrode through an insulator and vibrating in parallel to the electric lines of force; a pre-amplifier circuit connected to said detection electrode for amplifying the A.C. voltage signal and sending an amplified A.C. voltage signal; a drive circuit for vibrating said reed vibrator by applying a drive signal to a drive electrode of said reed vibrator; and induction noise removing means for removing induction noise imparted to the A.C. voltage signal by the drive signal, said induction noise removing means comprising a differential amplifier circuit receiving the amplified A.C. voltage signal and the drive signal as it inputs, amplifying a difference between said signals, and outputting an amplified difference signal. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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Specification