Appeal No. 2000-0142 Page 2
Application No. 08/705,569
BACKGROUND
The invention at issue in this appeal relates to a
ballast circuit for operating a discharge lamp. A
conventional voltage/current converter integrated circuit
(“IC”), which is used in such a ballast circuit, includes an
external reference resistor connected thereto. An external
bridge circuit generates a high-amplitude, high-frequency
voltage. A parasitic capacitance couples the voltage as a
high-frequency interference signal, which is superimposed on a
voltage developed across the reference resistor. Because the
reference resistor is part of a current amplifier of the
voltage/current converter and is coupled to a current source
of the converter, the current amplifier and the current source
are mutually interrelated. The interrelation produce a high-
frequency interference signal that impedes operation of the
IC.
The appellants’ ballast circuit includes a differential
amplifier. One input of the differential amplifier is
connected to a reference voltage; the other input, to a
reference resistor. A current generator supplies a first
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