The present invention relates generally to voltage regulator circuits and, more particularly, to a voltage regulator circuit incorporated in an integrated circuit.
Many of the modern electrical devices require power at voltages different from the nominal 110V or 220V supplied by utility companies to homes, offices and factories. Transformers or voltage regulators contained within the electrical devices usually provide the necessary voltage conversions. Voltage regulators also prevent surges or spikes in line voltage during start-up when an electrical device is switched on. The surges or spikes of voltage typically cause damage or failure of electrical or electronic circuits within the device unless a voltage regulator is included to control the spikes and surges. Thus, voltage regulators are important components of electrical circuits, particularly in regard to integrated circuits that are widely used in many electrical devices.
A prior art example of an on-chip voltage regulator circuit includes an operational amplifier referenced to a reference voltage (about 1.8V) that regulates the current supplying a transistor. A bandgap generator typically generates a stable voltage reference for the operational amplifier. An internal node Vdd is regulated to a midlevel voltage by the regulator circuit while an external Vdd voltage is supplied to the pin of the chip. When the current and, as a result, the voltage at the internal Vdd changes, the operational amplifier regulates a gate voltage of the transistor to supply the required current while keeping Vdd at a reference voltage.
During normal operation, since the difference between any two terminal voltages of the transistor would not exceed the reference voltage, there would not be any reliability problems. However, during startup the device capacitive members are not fully charged and the gate or the source of the transistor will approach the supply limit. This will result in a voltage corresponding to the supply limit being imposed across the gate oxide layer of the transistor, which exceeds the breakdown limit of the gate oxide and damages the transistor.
The present invention is directed to addressing the above and other needs in connection with improving a voltage regulator circuit that selectively couples the voltage of a voltage source to a voltage regulator circuit during device power-up. The present invention is exemplified in a number of implementations and applications, some of which are summarized below.
According to one aspect of the invention, it has been discovered that by appropriately biasing the main regulatory transistor of the voltage regulator circuit at start up the integrity of the transistor will be enhanced while the circuit loop stabilizes. The voltage regulator circuit includes a first current supplying transistor circuit disposed between the voltage source and the voltage drain, the first transistor circuit being regulated by a voltage referenced control circuit selectively coupled to control a gate of the first transistor circuit. A voltage biasing control circuit coupled to the gate of the first current supplying transistor circuit is adapted to provide a voltage bias to the first transistor circuit gate during power-up when the voltage referenced control circuit is electrically decoupled from controlling the first transistor circuit gate. The voltage referenced control circuit regulates a second current supplying transistor circuit disposed between the voltage source and the voltage drain. The voltage referenced control circuit is coupled to and continuously controls a gate of the second transistor circuit to maintain a control loop for the voltage regulator circuit during power-up.
According to another aspect of the invention, a voltage regulator circuit disposed between a voltage source and a voltage drain includes a first current supplying transistor member, disposed between the voltage source and the voltage drain, that is reversibly regulated by a voltage referenced operational amplifier. A voltage divider resistor ladder member, coupled in parallel with the first current supplying transistor, includes a first and a second resistor member in series. The resistor ladder member is reversibly regulated (or switchable) by the voltage referenced operational amplifier that is coupled to the ladder member at a node between the two resistive members. A second transistor member is coupled in parallel with the first current supplying transistor member and the voltage divider resistor ladder member and is irreversibly regulated (not switchable as in xe2x80x9creversibly regulatedxe2x80x9d) by the voltage referenced operational amplifier.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description which follow more particularly exemplify these embodiments.