Dialog Semiconductor Gmbh

Carlo Eberhard Peschke

Andreas Adler

Methods and systems to achieve linear and exponential control over a current to drive color LEDs have been achieved. Current digital-to-analog converters (IDAC) comprising each an exponential current digital-to analog converter and a linear IDAC, being cascaded to each other are used for a linear and an exponential control of a current driving a set of color LEDs, preferably RGB LEDs. The linear part of the IDAC, which is converting the mantissa of a floating-point number is used to control the color composition of the color LEDs. The exponential part of the IDAC, which is converting the exponent of the floating-point number is used to control the brightness of the color LEDs. While fading from one color to a next color a linear color change is required. The exponential part of the IDAC is used to dim the LEDs from bright to dark and vice versa. In order to get the visual perception of a linear dimming an exponential current change is required.

Combined exponential/linear RGB LED I-sink digital-to-analog converter

A high voltage digital output driver with dynamically biased cascode transistors is disclosed. The cascode transistors are dynamically self-biased via capacitors from the output voltage. The dynamic self-biasing doesn't require any switching means. The output-voltage can be increased by adding additional self-biased cascode transistors. The static current consumption in low-state for each individual driver on a same chip is minimal because only one resistor string consuming static current is required for all similar output drivers.

High voltage digital driver with dynamically biased cascode transistors

A charge pump circuit with a regulated charge current where the amount of current flowing into the flying capacitor depends on the magnitude of the output voltage error, using an OTA to convert the output voltage error into a current. Thus the flying capacitor is not charged when the output load is very low or when the output voltage error is minimal. Voltage overshoots are reduced by a stop circuit which forces pulse skipping and which inhibits the charging of the flying capacitor. Current limiting devices further limit the charge current into the flying capacitor. Full short-circuit protection is provided in one preferred embodiment by current limiting the driver stage of the charge pump circuit. Except for pulse skipping, the charge pump runs at a constant frequency supplied by a clock.

Voltage regulated charge pump with regulated charge current into the flying capacitor

Circuits and methods to convert a digital floating-point number into an analog current have been achieved. The conversion is performed directly by using an exponential current digital-to-analog converter (DAC) and a cascaded linear current digital-to-analog converter (DAC). The exponential current DAC is converting exponentially the exponent of the floating-point number, its output current is biasing the linear DAC, which is converting the mantissa of the floating-point number. The output current of the linear current DAC is correlates linearly with the value of the floating-point number. This technique is commutative, this means the sequence of the linear and the exponential converter can be interchanged. In this case the linear converter provides a biasing current to the exponential converter. The sign bit can be considered by converting the direction of the output current of the converter. This floating-point number conversion can handle a very high dynamic range and requires a minimum of chip space.

Floating point IDAC

A method for regulating the battery charge current with improved loop stability is achieved. Key element of this invention is a digital low pass filter within the feedback loop of the regulator, which is built by an up/down counter, a digital-to-analog-converter and a variable frequency oscillator. To achieve regulating loop stability in state-of-the-art analog designs, the dominant pole has to be selected at a sufficiently low frequency, which causes the regulator to be too slow for pulsed charge currents. The disclosed invention replaces the analog feedback circuit with a digital low pass filter arrangement. It achieves stability by being able to choose the low pass filter time constant longer than the supply-voltage-pulse-width with reduced circuit complexity and less electronic circuit resources. Furthermore, the timing characteristics can be varied during normal operation by modifying the oscillator frequency and by presetting the up/down counter to defined values. The circuit is capable of regulating a charge current from a pulsed power supply, such as a rectified sine wave power supply without capacitor and can provide a pulse-width-modulated charge current. The circuit makes sure that the maximum peak current of the battery isn't exceeded by sampling only when there is sufficient supply voltage.

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Kirchheim/Teck-Nabern, Germany

Carlo Eberhard Peschke