Current control circuit

Details Current control circuit Current control circuit

1988-12-02

1990-02-20

Tarcza, Thomas H.

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Cathode-ray deflections circuits

315387, H01J 2958, H01J 2970

Patent

active

049029401

ABSTRACT:
A current control circuit is provided for a stigmator lens of an electron or ion beam machine. The stigmator lens consists of two magnetic quadrupole lenses, each of which has two pairs of coils. Current monitoring resistors R10,R11,R12 and R13 are connected in series with the individual coils L1,L2,L3 and L4 of the quadrupole and a resistor R3 is connected to monitor the sum of currents in the pairs of coils. Voltage signals from the resistors are used to close feedback loops which drive currents into the individual coils so that the sum of currents in a pair of coils is held constant at a value set by an adjustable astigmatism control and so that the ratio of the currents in a pair of coils is held constant at a value set by an adjustable beam centering control. Coil currents are stabilized in spite of coil resistance changes due to Joule heating by the currents. Computer control of astigmatism and centering is facilitated since only signal voltages are required as inputs to the circuit.

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