US 6,982,689 B2 | ||
Light-emitting element drive apparatus | ||
Tsukasa Hoshi, Sendai (Japan); and Hiroshi Sakamoto, Tokyo (Japan) | ||
Assigned to Freescale Semiconductor, INC, Austin, Tex. (US) | ||
Filed on May 22, 2003, as Appl. No. 10/443,376. | ||
Claims priority of application No. 2002-151263 (JP), filed on May 24, 2002. | ||
Prior Publication US 2003/0218585 A1, Nov. 27, 2003 | ||
Int. Cl. G09G 3/34 (2006.01) |
U.S. Cl. 345—84 | 7 Claims |
1. A light-emitting element drive apparatus, comprising;
a drive current generation circuit for outputting a drive current to a light-emitting element, the drive current causing the
light-emitting element to emit light with a predetermined optical output based on a data signal;
a sensing light-receiving element for receiving light from the light-emitting element and outputting a sense signal that corresponds
to the optical output thereof;
a first filter for smoothing the sense signal;
a first comparison circuit for comparing the smoothed sense signal from the first filter and a pre-determined setup signal;
a control circuit for generating, based on a comparison result of the first comparison circuit, a control signal that causes
the drive current generation circuit to output the drive current such that the light-emitting element produces the predetermined
optical output;
a setup signal generation circuit that waveform-shapes the setup signal so that the setup signal has the same ripple component
as the smoothed sense signal, and outputs the waveform shaped setup signal to the first comparison circuit in synchronization
with the smoothed sense signal;
a level adjustment circuit for receiving the setup signal from the setup signal generation circuit and attenuating the setup
signal to a pre-determined level to generate a light-emitting element degradation setup signal; and
a second comparison circuit for comparing the light-emitting element degradation setup signal and the smoothed sense signal
from the first filter to determine whether the light-emitting element has degraded.
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