# Patent

## Title
Voltage regulator for high performance RF systems

## Abstract

A voltage regulator for a radio frequency circuit including a master regulator circuit, a first slave regulator circuit, and a first radio frequency subcircuit. The master regulator circuit is configured to i) receive a reference voltage signal and a feedback signal and ii) output a control voltage signal based on the reference voltage signal and the feedback signal. The first slave regulator circuit is configured to i) receive the control voltage signal and ii) output a first regulated supply voltage signal based on the control voltage signal. The first radio frequency subcircuit is configured to receive the first regulated supply voltage signal. The control voltage signal corresponds to a desired supply voltage for the first radio frequency subcircuit.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 11/715,027 filed on Mar. 7, 2007, which is a continuation of U.S. patent application Ser. No. 10/747,522 filed on Dec. 29, 2003 (now U.S. Pat. No. 7,190,936, dated Mar. 13, 2007), which application claims the benefit of U.S. Provisional Application No. 60/470,620, filed on May 15, 2003. The disclosures of the above applications are incorporated herein by reference.


FIELD OF THE INVENTION
The present invention relates to voltage regulators, and more particularly to voltage regulators for high performance radio frequency (RF) systems.
BACKGROUND OF THE INVENTION
Circuits in high performance radio frequency (RF) systems such as but not limited to wireless communications devices often require a regulated supply voltage. Voltage regulators are typically used to regulate the supply voltage. In some RF systems, more than one voltage regulator may be required. In other applications with spatial limitations, multiple circuits may share the same voltage regulator. For example, a voltage-controlled oscillator (VCO) circuit and a mixer circuit may share the same regulated supply. In this configuration, noise from the mixer circuit often appears at the output of the VCO circuit and vice-versa.
Referring now to FIG. 1, an exemplary voltage regulator 10 includes an operational amplifier (opamp) 12 and a PMOS transistor 14. An inverting input of the opamp 12 receives a reference voltage signal 16 and a non-inverting input of the opamp 12 receives a feedback signal 18. The opamp 12 generates an output voltage signal 20 that is based on a difference between the reference voltage signal 16 and the feedback signal 18.
The output voltage signal 20 is input to a gate of the PMOS transistor 14. A source of the PMOS transistor 14 is connected to a supply voltage 22. A drain of the PMOS transistor 14 is connected to the non-inverting input of the opamp 12 to provide the feedback signal 18. The voltage regulator 10 outputs a regulated signal 26 to an RF subcircuit 28 of a RF system 30. When supplying a single RF subcircuit 28, the regulated signal 26 is stable and constant. When a single voltage regulator supplies more than one RF subcircuit, noise or crosstalk from one of the RF sub-circuits may appear in the output of the other RF sub-circuit.
Referring now to FIG. 2, separate voltage regulators may be used for each subcircuit to eliminate the noise. The RF circuit 30 includes n RF subcircuits 28-1, . . . , 28-n that require voltage regulation. Voltage regulators 10-1, . . . , 10-n are provided for each RF subcircuit 28-1, . . . , 28-n, respectively. The voltage regulators 10-1, . . . , 10-n include opamps 12-1, . . . , 12-n, and transistors 14-1, . . . , 14n, respectively. Feedback signals 18-1, . . . , 18-n are generated as described above. When multiple voltage regulators 10-1, . . . , 10n are used, the spatial requirements and current dissipation of the RF system 30 increase.
SUMMARY OF THE INVENTION
A voltage regulator according to the present invention includes a master regulator circuit that receives a reference signal, that generates a master bias signal and that includes a transistor having a first gain. A first slave regulator circuit includes a first transistor having a second gain that is substantially equal to unity gain, a control terminal that receives the master bias signal from the master regulator circuit, a first terminal and a second terminal that outputs a first regulated output signal. A second slave regulator circuit includes a second transistor having a third gain that is substantially equal to unity gain, a control terminal that receives the master bias signal from the master regulator circuit, a first terminal, and a second terminal that outputs a second regulated output signal.
In other features, the master regulator circuit includes an opamp having a non-inverting input that receives the reference signal, an inverting input and an output. The output of the opamp generates the master bias signal, which is output to a control terminal of the transistor.
In yet other features, the master regulator circuit includes a current source. A second terminal of the transistor communicates with the current source and the inverting input of the opamp. The transistor includes a first terminal. The first terminals of the transistor, the first transistor and the second transistor are biased by a first voltage potential.
In still other features, the transistor, the first transistor and the second transistor are NMOS transistors. The first gain is greater than unity gain.
In still other features, a Radio Frequency (RF) circuit includes the voltage regulator, a first RF subcircuit that receives the first regulated output signal, and a second RF subcircuit that receives the second regulated output signal. The RF circuit is a wireless communications device.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1 is a schematic of an exemplary voltage regulator according to the prior art;
FIG. 2 is a schematic of an RF circuit with multiple RF subcircuits and voltage regulators with feedback circuits according to the prior art;
FIG. 3 is a functional block diagram of a voltage regulator with a master and multiple slave regulator circuits according to the present invention;
FIG. 4 is an electric schematic of the voltage regulator of FIG. 3; and
FIG. 5 is a functional block diagram of the voltage regulator of FIG. 3 implemented in an RF transceiver of a wireless communications device.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements.
Referring now to FIG. 3, a voltage regulator 40 includes a master regulator circuit 44 and one or more slave regulator circuits 46-1, 46-2, . . . , and 46-m (collectively identified as slave regulator circuits 46). The master regulator circuit 44 receives a reference voltage signal 48 and generates a master bias signal 50, as will be described below. The slave regulator circuits 46 receive the master bias signal 50 from the master regulator circuit 44. The slave regulator circuits 46 output a regulated signal 54 based on the master bias signal 50. RF subcircuits 56-1, 56-2, . . . , and 56-m (collectively identified as RF subcircuits 56) receive the regulated signal 54. Because the desired supply voltage for the RF subcircuit 56 is sensed and adjusted at the master regulator circuit 44, the slave regulator circuits 46 operate as level shifters and unity gain buffers and have feedback. The slave regulator circuits 46 have a second gain that is substantially equal to unity gain. As used herein, the term substantially equally to unity gain means a gain that is greater than 0.5 and less than 2.
Referring now to FIG. 4, the master regulator circuit 44 includes an opamp 60, a first NMOS transistor 62, and a current source 64. The reference voltage signal 48 communicates with a non-inverting input 66 of the opamp 60. The opamp 60 outputs the master bias signal 50, which biases a gate terminal 70 of the first NMOS transistor 62. A drain terminal 72 of the first NMOS transistor 62 communicates with a supply voltage 74. A source terminal 78 of the first NMOS transistor 62 communicates with an inverting input 68 of the opamp 60 to provide a feedback signal 52 and with the current source 64, which is referenced to a ground potential 80.
The master bias signal 50 is regulated based on a difference between the reference voltage signal 48 and the feedback signal 52. The master bias signal 50 is output to slave regulator circuits 82-1, 82-2, . . . , 82-m. The slave regulator circuits 82-1, 82-2, . . . , 82-m include second NMOS transistors 84-1, 84-2, . . . , 84-m. The slave regulator circuits 82-1, 82-2, . . . , 82-m provide a regulated signal to RF subcircuits 86-1, 86-2, . . . , 86-m of the RF system 30. The master bias signal 50 biases gates 88-1, 88-2, . . . , 88-m of the second NMOS transistors 84-1, 84-2, . . . , 84-m. Drain terminals 90-1, 90-2, . . . , 90-N of the second NMOS transistors 84-1, 84-2, . . . , 84-m communicate with a supply voltage 74-1, 74-2, . . . , 74-m. Source terminals 92-1, 92-2, . . . , 92-m of the second NMOS transistors 84-1, 84-2, . . . , 84-m output a regulated supply voltage signal 94-1, 94-2, . . . , 94-m to the RF subcircuits 86-1, 86-2, . . . , 86-m. In this arrangement, the second NMOS transistors 84-1, 84-2, . . . , 84-m act as source followers.
The regulated supply voltage 94-1, 94-2, . . . , 94-m is based on a difference between the reference voltage signal 48 and the feedback signal 52, which is generated in the master regulator circuit 44. Because the second NMOS transistors 84-1, 84-2, . . . , 84-m have substantially unity gain, the slave regulator circuits 82-1, 82-2, . . . , 82-m act as unity gain buffers for the master control voltage signal 50. In conventional regulator circuits shown in FIGS. 1 and 2, a small change in the output signal 20 can significantly impact the regulated signal 26 that is input to the circuit blocks 28 because the PMOS transistor 14 does not have unity gain.
Referring now to FIG. 5, the master regulator 44 and slave regulators 46-1, 46-2, . . . , 46-m can be used in wireless communication devices. In one implementation, a wireless communications device 100 is connected to a host device 102 such as but not limited to a desktop computer, a personal digital assistant (PDA), a laptop computer, a gaming console, an access point and the like. The wireless communications device 100 further includes a medium access control (MAC) device 104 and an RF transceiver 108. The master regulator 44 and slave regulators 46-1, 46-2, . . . , and 46-m supply regulated outputs to RF subcircuits 110-1, 110-2, . . . , and 110-m of the RF transceiver 108. In one implementation, the wireless communications device is compliant with at least one of IEEE 802.11, 802.11a, 802.11g, 802.11n, and/or 802.16, which are hereby incorporated by reference in their entirety, although other existing and future wireless standards may be used.
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.

## Claims

1. A voltage regulator for a radio frequency circuit, the voltage regulator comprising:
a master regulator circuit configured to i) receive a reference voltage signal and a feedback signal and ii) output a control voltage signal based on the reference voltage signal and the feedback signal;
a first slave regulator circuit configured to i) receive the control voltage signal and ii) output a first regulated supply voltage signal based on the control voltage signal; and
a first radio frequency subcircuit configured to receive the first regulated supply voltage signal, wherein the control voltage signal corresponds to a desired supply voltage for the first radio frequency subcircuit.

2. The voltage regulator of claim 1, further comprising:
a second slave regulator circuit configured to i) receive the control voltage signal and ii) output a second regulated supply voltage signal based on the control voltage signal; and
a second radio frequency subcircuit configured to receive the second regulated supply voltage signal, wherein the control voltage signal corresponds to a desired supply voltage for the second radio frequency subcircuit.

3. The voltage regulator of claim 1, wherein:
the master regulator circuit has a first gain; and
the first slave regulator circuit has a second gain that is different than the first gain.

4. The voltage regulator of claim 1, wherein a gain of the first slave regulator circuit is substantially equal to unity gain.

5. The voltage regulator of claim 1, wherein the first regulated supply voltage signal corresponds to a difference between the reference voltage signal and the feedback signal.

6. The voltage regulator of claim 1, wherein:
the master regulator circuit includes a first transistor having a first gain; and
the first slave regulator circuit includes a second transistor having a second gain that is different than the first gain.

7. The voltage regulator of claim 1, wherein:
the master regulator circuit includes a first transistor; and
the first slave regulator circuit includes a second transistor configured as a source follower.

8. The voltage regulator of claim 1, wherein:
the master regulator circuit includes a first transistor;
the first slave regulator circuit includes a second transistor; and
the control voltage signal biases a gate of the second transistor.

9. The voltage regulator of claim 1, wherein the master regulator circuit includes an operational amplifier configured to i) receive the reference voltage signal and the feedback signal and ii) output the control voltage signal.

10. A method of operating voltage regulator for a radio frequency circuit, the method comprising:
using a master regulator circuit, i) receiving a reference voltage signal and a feedback signal and ii) outputting a control voltage signal based on the reference voltage signal and the feedback signal;
using a first slave regulator circuit, i) receiving the control voltage signal and ii) outputting a first regulated supply voltage signal based on the control voltage signal; and
using a first radio frequency subcircuit, receiving the first regulated supply voltage signal, wherein the control voltage signal corresponds to a desired supply voltage for the first radio frequency subcircuit.

11. The method of claim 10, further comprising:
using a second slave regulator circuit, i) receiving the control voltage signal and ii) outputting a second regulated supply voltage signal based on the control voltage signal; and
using a second radio frequency subcircuit, receiving the second regulated supply voltage signal, wherein the control voltage signal corresponds to a desired supply voltage for the second radio frequency subcircuit.

12. The method of claim 10, further comprising:
configuring the master regulator circuit to have a first gain; and
configuring the first slave regulator circuit to have a second gain that is different than the first gain.

13. The method of claim 10, further comprising configuring a gain of the first slave regulator circuit to be substantially equal to unity gain.

14. The method of claim 10, wherein the first regulated supply voltage signal corresponds to a difference between the reference voltage signal and the feedback signal.

15. The method of claim 10, wherein:
the master regulator circuit includes a first transistor having a first gain; and
the first slave regulator circuit includes a second transistor having a second gain that is different than the first gain.

16. The method of claim 10, wherein:
the master regulator circuit includes a first transistor; and
the first slave regulator circuit includes a second transistor configured as a source follower.

17. The method of claim 10, wherein:
the master regulator circuit includes a first transistor;
the first slave regulator circuit includes a second transistor; and
the method further comprises biasing a gate of the second transistor with the control voltage signal.

18. The method of claim 10, further comprising:
receiving the reference voltage signal and the feedback signal at an operational amplifier of the master regulator circuit; and
outputting the control voltage signal using the operational amplifier.