A small-area low-mismatch multi-channel constant current LED driver
This paper proposes a new structure of LED(Light-emitting diode) driver for obtaining a low mismatch output current between different channels and even reduces the chip area. It's fabricated with TSMC 0.35µm DDD process. The chip contains 16 channels and the maximum/minimum output current is 3mA/45mA, respectively. The value of each channel's output current is the same and controlled by a programmable 6-bits digital input signals. The circuit uses constant gate voltage of the power MOS working in the linear region whose (Vgs — Vth) is 10 to 50 times of Vds. The advantage is no DAC(Digital-to-Analog Converter) and no complex gate voltage generating circuit. Simple gate voltage generating circuit can also adapt to a wide range of external resistance changes. Because of the lower mismatch caused by threshold voltage mismatch, it can achieve a highly matched output current. The chip has only ±1.1% mismatch between different channels. The area of each channel's power MOS is only 200µm× 100µm. The area of analog part including current bias, bandgap reference, current mirror, and other control circuits is only 400µm×200µm.