Circuit for reducing ELF electric fields radiated from CRT devices
AssigneeApple Computer, Inc.
InventorRichard D. Cappels, Sr.
Life of this patent
Estimating the term…
Abstract
A circuit for reducing extremely low frequency (ELF) electric fields on cathode ray robe (CRT) devices comprises a power supply means, a CRT, a voltage sensing means, an amplification means, and a capacitive coupling within a feedback path to the CRT. A CRT anode voltage variation sensed by the voltage sensing means is amplified and inverted by the amplification means, producing a signal which is applied to the capacitive coupling within the feedback path. This signal modifies the impedance at the CRT anode, decreasing the voltage variation and thereby reducing ELF electric field magnitudes.
Claims16
A circuit for reducing ELF electric fields radiated from CRT devices, the circuit comprising:
- a CRT having a cathode and an anode;
- power supply means electrically coupled between the anode and the cathode for providing bias to the CRT;
- amplification means having a first input electrically coupled to the power supply means and to the anode, and an output electrically coupled to the anode, for supplying an amplified anode voltage variation signal to the anode;
- and
- a capacitor coupled between the amplification means and the anode, the coupling maintained by the capacitor for lowering the anode impedance such that the resulting anode impedance is inversely related to the product of the capacitance of the capacitor and the voltage gain of the amplification means.
A method for reducing ELF electric fields radiated from CRT devices having an anode and a cathode, wherein the CRT is biased from a power supply, the method comprising the steps of:
- applying a voltage signal from the power supply, the voltage signal applied between the anode and the cathode of the CRT;
- applying an amplified anode voltage variation signal to the anode from an amplifier electrically coupled to the power supply and the anode;
- and
- capacitively coupling the amplifier to the anode in order to lower the anode impedance by an amount inversely proportional to the product of the capacitance of the capacitor and the gain of the amplifier.
Dependencies are inferred from the claim text.