Abstract: The present invention uses two transistors instead of a sensing resistor to provide a constant current source for a load such as an array of light emitting diodes (“LEDs”). In the present invention, a bias current is applied to a branch of the circuit. The drain-to-source voltages of two transistors are matched. The voltage at the gate of both transistors is controlled based on the bias current and the drain-to-source current of the first of the two transistors. The second of the two transistors is sized such that source current of the second transistor is a multiple of the source current of the first transistor for a given gate voltage. By the techniques of this invention, the load current in a circuit is efficiently kept constant at a multiple of the input bias current.

Abstract: The techniques of the present invention relate to automatically controlling display intensity. The present invention includes a calibration step in which the display intensity settings are correlated to the ambient light intensity conditions. The present invention also includes an automatic adjustment step in which the ambient light intensity is measured and the display intensity is automatically adjusted according to a correlation defined in the calibration step.

Abstract: The present invention provides a controller for regulating current in LEDs in electronic displays. The controller uses temperature sensing diodes to detect changes in the LED ambient temperature. As the LED ambient temperature changes, the forward voltage of the temperature sensing diode decreases. A signal processor adjusts the current passing through the LEDs based on the temperature induced changes in the forward voltage of the temperature sensing diodes. The present invention can reduce costs over the present methods of regulating current in LEDs and may more easily be integrated into a single integrated circuit chip. The temperature sensing may also be implemented outside the integrated circuit chip.

Abstract: The present invention provides a controller for controlling strings of LEDs in a liquid crystal display. The hybrid controller uses both analog and digital circuit components. Error amplifiers are used to compare analog feedback signals received from the LED strings with reference signals. The results of those comparisons are converted to digital data and processed by a digital signal processor (DSP). The DSP calculates the drive voltages for the LED strings based on the deviation between the actual current flows (represented by feedback signals) and the desired current flows (represented by reference signals) through the LED strings. Analog drivers provide the drive voltages to the LED strings.

Abstract: The present invention relates to displays that use LED strings for backlighting. A lead string is provided with continuous drive voltage and the non-lead strings are provided with pulsed drive pulses. The string having the highest forward voltage is selected as the lead string. Feedback information indicative of the currents flowing through the non-lead strings is used to determine the duty cycles of the voltage pulses provided to drive the non-lead strings. The non-lead strings are controlled using pulsed drive voltages to minimize power dissipation in the circuit.