Voltage regulator having error and transconductance amplifiers to define multiple poles

摘要

A voltage regulator and method of voltage regulation utilizes an error amplifier and a transconductance amplifier together with a voltage reference, startup circuit and output load. The use of the transconductance amplifier allows the use of an arrangement of two poles and a zero such that the composite gain roll-off has a generally constant slope. One of the poles utilized in this stability scheme is the outer pole formed by the resistive-like load and its filter capacitor. Another pole and zero are generated in the error amplifier circuit. To decouple the noisy input supply voltage, sensitive parts of the circuit are powered by the regulated output voltage. A start circuit is provided to start up the output and voltage reference when no output voltage is present. The transconductance amplifier block has special characteristics which allow it to work to relatively high frequency, above the gain bandwidth product of the control loop. It is driven by a fully differential push-pull, class AB amplifier. The transconductance amplifier utilizes a current mirror approach to current sensing in the output device which utilizes cascode techniques for more accurate current sensing in the current mirror.