High bandwidth, high PSRR, low dropout voltage regulator
View Patent ↗A voltage regulator may include one or more features for generating high PSRR. For example, source follower devices may be included in the voltage regulator for providing current sources for the output voltage nodes. The source followers may be sensitive to power supply noise at the gate terminal. Filters are included on the gate terminals to filter the power supply noise, thus reducing the noise at the gate terminals. As another example, the voltage regulator may employ current sources on the output voltage nodes which produce current inversely proportional to the current drawn by the load. In one embodiment, the voltage regulator may include a power control circuit used to provide overvoltage protection during power up. The power control circuit provides a voltage during power up, and ceases providing the voltage after a time interval so that the circuit may operate.
1. A circuit comprising:
an operational amplifier;
a source follower transistor coupled to a power supply to provide a voltage at its source terminal, in which the source terminal has a low output impedance, the source follower transistor also having filtering to reduce noise from the power supply;
a first transistor having a gate terminal coupled to an output of the operational amplifier and also having a first terminal coupled to the source terminal of the source follower transistor and a second terminal coupled to an output node to provide an output voltage to which a load is to be coupled, in which the load is operable to draw a first current from the output node during operation; and
a second transistor coupled to the first transistor to draw a second current from the output node which is inversely proportional to the first current drawn by the load during operation to maintain a substantially constant current through the first transistor to regulate the output voltage, wherein a gate terminal of the second transistor is coupled to the output of the operational amplifier and wherein the second transistor has a third terminal coupled to the output node and a fourth terminal coupled to a supply return.
2. The circuit as recited in claim 1 wherein the second transistor is an N-type transistor.
3. The circuit as recited in claim 1 wherein the output node is coupled to an input terminal of the operational amplifier through a feedback network.