Beam current measurement

Abstract

The display apparatus comprises a picture tube (CRT) with an electron gun which generates an electron beam (BB) directed towards a display screen. The electron gun comprises a first and a second electrode (CA, G1). The electron beam (EB) originates from the first electrode (CA). The voltage between the first electrode (CA) and the second electrode ( G1) controls the intensity of the electron beam (EB). A beam current (IB) flows in the first electrode (CA) in response to the electron beam (EB). A (ICA) in the first electrode (CA) is the sum of the beam current (IB) and a current (IC) flowing through a capacitance (CWN) between the first and the second electrode (CA, G1). A compensation circuit (COM) supplies a compensation current (ICO) to the first electrode (CA) to compensate for a capacitive current (IC) through a capacitance (CIN) between the first and the second electrode (CA, G1). A beam current measurement circuit (BMC) measures the total current (IT) which is the sum of the total current in the first electrode (ICA) and the compensation current (ICO).

Dependencies are inferred from the claim text.