High bandwidth, high PSRR, low dropout voltage regulator

• US 7,132,880 B2
• Filed: 06/07/2005
• Issued: 11/07/2006
• Est. Priority Date: 02/02/2001
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Ingino, Joseph M. Jr.
• Primary Examiner(s): TRA, ANH QUAN
• Application Number:
  US11/146,448
• Publication Number:
  US 20050225380A1
• Time in Patent Office: 518 Days
• Field of Search: 327/538, 327540-541, 327/543, 323/280, 323/281, 323/316
• US Class Current: 327/541
• CPC Class Codes: G05F 1/575 characterised by the feedback circuit
• CPC Class Codes: G05F 3/262 using field-effect transistors only
• CPC Class Codes: G05F 3/30 Regulators using the difference between the base-emitter voltages of two bipolar transistors operating at different current densities G05F3/26 takes precedence
• CPC Class Codes: H03K 17/223 in field-effect transistor switches
• CPC Class Codes: H03K 3/0315 Ring oscillators
• CPC Class Codes: H03L 7/0896 the current generators being controlled by differential up-down pulses
• CPC Class Codes: H03L 7/0898 the source or sink current values being variable H03L7/0896 takes precedence
• CPC Class Codes: H03L 7/093 using special filtering or amplification characteristics in the loop H03L7/087 - H03L7/091 take precedence
• CPC Class Codes: H03L 7/0995 the oscillator comprising a ring oscillator
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence
• CPC Class Codes: Y10S 323/901 Starting circuits

Abstract

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.

Claims

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.