Method and system for sequential calibration of matched current sources

Abstract

The present invention discloses a system and a method for sequential calibration of matched current sources. The system involves LED strings and programmable current source circuits (CSC). An LED current flows through each LED string. Each LED current is controlled by an associated programmable CSC. In one embodiment, the CSCs form a chain. A first CSC uses a reference current for calibration, and thereafter supplies the reference current to the next CSC. When the next CSC detects the reference current, it uses the reference current for calibration. CSCs are calibrated one by one down the chain. In a second embodiment, each CSC can receive the reference current from a common conductor. If the common conductor is detected to be available, then the CSC uses the reference current for calibration. When the conductor is in use, the other CSCs detect the conductor as unavailable and do not attempt to self-calibrate. The CSCs use the reference current one by one, but in an order that changes over time.

Description

technical field [0001] The present invention relates generally to scaling current through a plurality of current sources, and more particularly to scaling current through strings of white light emitting diodes (WLEDs) for backlighting displays. Background technique [0002] New developments in WLED (White Light Emitting Diode) technology have resulted in cost-effective large-array WLEDs for backlighting applications in LCD screens for notebook computers, personal digital assistants, and flat-panel televisions. There are applications requiring hundreds of WLEDs today and thousands of WLEDs may be employed in future applications. [0003] These large arrays often consist of parallel connections of series strings of WLEDs. For example a typical array might have 12 parallel strings, with each string having ten WLEDs in series for a total of one hundred and twenty WLEDs. [0004] figure 1 (Prior Art) is a schematic diagram of an LCD display 1 employing 12 strings of WLEDs for ...

AI Technical Summary

Problems solved by technology

The problem is that the current reference of one integrated circuit 13 may not match the current reference of another integrated circuit 15 used in the same large array

The circuit of Figure 7 has some problems because the voltage drop along the ground line 34 of a large LCD display will effectively change the reference voltage that each integrated circuit "sees" as a person moves along the ground line 34 from integrated circuit to integrated circuit

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