Silanna Asia Pte Ltd

Mediatek Singapore Pte. Ltd.

Plx Technology, Inc.

Rawinder Dharmalinggam

Tiong Lim

Kok Soon Yeo

Kais Badami

Chinq-Shiun Chiu

Wee Liang Lien

Kanan Saurabh

Ten Voon Wong

An improved power converter produces power through a power switch in response to an activation signal that has an on-time and a switching frequency. An on-time signal has a constant on-time and controls the on-time of the activation signal. An error signal indicates that the switching frequency is not equal to a reference frequency. A step up signal and a step down signal are based on the error signal. A count signal is increased in response to the step up signal and decreased in response to the step down signal. An on-time pulse has a duration that is related to a value of the count signal. The on-time pulse controls the constant on-time of the on-time signal and maintains the switching frequency at about the reference frequency.

Constant on-time converter with frequency control

During a first mode of operation, a zero current detect (ZCD) signal is asserted in response to detecting a zero current condition at a switch node of a power converter. The power converter enters a light load mode of operation when the ZCD signal is asserted between a beginning point and a trigger point of a period of a PWM signal. A compensator voltage is generated based on a feedback voltage indicative of an output voltage. The compensator voltage is compared to a threshold voltage that represents a limit for the compensator voltage during the light load mode of operation determined over a range of the output voltage. The power converter exits the light load mode back to the first mode of operation in response to the compensator voltage being beyond the threshold voltage.

Light load mode entry or exit for power converter

A voltage controlled oscillator and a load cell circuit usable in VCO are provided. The VCO features an internal compensation for process, voltage and temperature using a replica of half of the oscillating stage. The load cell circuit comprises a bias transistor to drain a predetermined current from the oscillating stage, a control transistor to vary resistance offered by it responsive to a control voltage applied and a resistor adapted to provide a clamp resistance.

Circuit for voltage controlled oscillator

A variable gain amplifying circuit comprises two stages, a first stage and a second stage with a common voltage-to-current converter. Each stage comprises two BJTs, two voltage controlled current sources, a variable resistor with a variable resistance, and the common voltage-to-current converter. The two BJTs construct a differential amplifier for amplifying a pair of differential signals. The variable resistor with the variable resistance is connected between the emitters of the two BJTs wherein the variable resistance of the variable resistor is represented as R. The variable resistance Ris controlled by a control voltage V. The two voltage controlled current sources are respectively connected between the corresponding emitter of BJTs and ground. The currents respectively through the voltage controlled current sources are equal to each other and represented as I. The current Iis controlled by the common voltage-to-current converter according the control voltage V. The variable resistance Rand the current Iof the voltage controlled current sources can be varied simultaneously by the control voltage Vso as to rapidly adjust the gain of the variable gain amplifying circuit.

Variable gain amplifying circuit

A tuning circuit for tuning an active filter includes a resistor-capacitor circuit comprising a variable capacitor and a resistor equivalent to a first resistor and a second resistor serially connected to the first resistor, a voltage generator for providing a constant reference voltage to the first resistor, a current replicating unit for replicating a current based on the constant reference voltage, a comparator for comparing a charging voltage as the current is charging a variable capacitor with the constant reference voltage, a counter for counting a number of cycles of a clock signal until the charging voltage reaches the constant reference voltage, a adjustment unit for calibrating a capacitance of the variable capacitor based on the number of cycles of a clock signal and a target count value associated with a predetermined RC time constant.

Growing community of inventors

Singapore, Singapore

Rawinder Dharmalinggam