Patent Application
20130099764
The present disclosure is generally related to a system and method of regulating voltage.
Advances in technology have resulted in smaller and more powerful computing devices. For example, there currently exist a variety of portable personal computing devices, including wireless computing devices, such as portable wireless telephones, personal digital assistants (PDAs), and paging devices that are small, lightweight, and easily carried by users. More specifically, portable wireless telephones, such as cellular telephones and Internet Protocol (IP) telephones, can communicate voice and data packets over wireless networks. Many such wireless telephones incorporate additional devices to provide enhanced functionality for end users. For example, a wireless telephone can also include a digital still camera, a digital video camera, a digital recorder, and an audio file player. Also, such wireless telephones can process executable instructions, including software applications, such as a web browser application, that can be used to access the Internet. As such, these wireless telephones can include significant computing capabilities.
Such computing devices often use steady voltage supplies provided by voltage regulators, such as low drop-out (LDO) regulators. LDO regulators are particularly suited for use in portable electronic devices due to their small size and interoperability. LDO regulators balance stability considerations with power supply and space constraints and may be used to provide a constant output voltage.
In a particular embodiment, a voltage regulator enables frequency compensation to maintain a constant voltage level using a low input power. The frequency response of the voltage regulator may be stabilized by adjusting capacitance and transistor transconductance values to cause a zero to substantially track variations in an output pole.
In another particular embodiment, a voltage regulator includes an error amplifier, a voltage buffer responsive to the error amplifier, and a first transistor responsive to the voltage buffer and coupled to a voltage supply source. A second transistor is coupled to the voltage supply source and is further coupled to an output node. A third transistor is coupled to the first transistor and has a gate coupled to a capacitor. The capacitor is coupled to a node between the error amplifier and the voltage buffer.
In a particular embodiment, a method of regulating voltages includes receiving an unregulated voltage at a first transistor and at a second transistor. A third transistor is biased based on a bias current from the first transistor. The first transistor and the second transistor are responsive to an error voltage generated by an error amplifier that is responsive to a reference voltage and to an output node of a voltage regulator via a feedback path.
In another particular embodiment, an apparatus includes a semiconductor device that includes a first voltage island and a second voltage island. A first voltage regulator on the first voltage island is configured to power the first voltage island. A second voltage regulator on the second voltage island is configured to power the second voltage island. The first voltage regulator and the second voltage regulator each include a first transistor, a second transistor, a third transistor, and a capacitor. The capacitor has a value of less than 300 picofarads (pF).
One particular advantage provided by at least one of the disclosed embodiments includes enabling voltage regulation with a low power supply. Embodiments may also include small capacitor sizes and frequency stability compensation.
Other aspects, advantages, and features of the present disclosure will become apparent after review of the entire application, including the following sections: Brief Description of the Drawings, Detailed Description, and the Claims.
A voltage regulator may be used to automatically maintain a constant voltage level, such as to provide a steady voltage supply to portable electronic devices. The voltage regulator may operate by comparing an output voltage to a reference voltage. A detected difference may be amplified and used to reduce voltage error. A particular embodiment may adjust a frequency response by causing a zero in an open loop gain to change position according to an output pole associated with the output voltage. The zero may offset the output pole to stabilize the voltage regulator.
Referring to
A frequency within the voltage regulator 100 may be stabilized by manipulating capacitance and transistor transconductance values. The manipulated values may cause a zero to substantially track variations in an output pole towards stabilizing the voltage regulator 100 and maintaining a constant voltage. The output pole may be associated with an output node 104 of the voltage regulator 100. A pole may generally define a frequency that makes a gain of a filter transfer function infinite (e.g., a denominator of the transfer function equals zero). The zero may be associated with a circuit arrangement that includes a gain of the first transistor 110 and the third transistor 116 combined with a capacitance of the capacitor 120. A zero may generally define a frequency that makes a gain of a filter transfer function zero (e.g., a numerator of the transfer function equals zero). The gain of the first transistor 110 and the third transistor 116 and the capacitance may create a Miller effect to increase an effective capacitance. The effective capacitance may facilitate both a smaller capacitor size of the capacitor 120 and a smaller voltage supply.
The error amplifier 102 may be configured to generate an error voltage 121. The error amplifier 102 may be responsive to the feedback path 106 that is coupled to the output node 104 and that includes at least a portion of the load 123. For example, a signal associated with an output current from the output node 104 may be provided to the second input 105 of the error amplifier 102 via the feedback path 106.
The voltage buffer 108 may be responsive to the error amplifier 102. For example, the voltage buffer 108 may generate a buffered output in response to receiving the error voltage 121 from the error amplifier 102.
The first transistor 110 may be responsive to the output of the voltage buffer 108 and therefore to the error voltage 121 generated by the error amplifier 102. The source of the first transistor 110 may receive an unregulated voltage from the voltage supply source VIN 128. According to a particular embodiment, the voltage regulator 100 may be configured to operate when the voltage supply source VIN 128 is less than one volt, as well as at higher voltage levels.
According to a particular embodiment, the first transistor 110 may be configured to mirror the second transistor 114. Hence, a current output of the first transistor 110 may vary according to a current output of the second transistor 114. The first transistor 110 may be configured to generate a bias current 134 that is provided to the drain 115 of the third transistor 116.
The source of the second transistor 114 may receive the unregulated voltage from the voltage supply source VIN 128. The drain of the second transistor 114 may be coupled to the output node 104. The second transistor 114 may be a power transistor that is responsive to the error voltage 121 generated by the error amplifier 102 via the voltage buffer 108. According to a particular embodiment, the second transistor 114 may be a thin-oxide transistor to conserve space. The second transistor 114 may be smaller than the first transistor 110 and the third transistor 116.
The drain of the second transistor 114 may be coupled to the load 123 (the load 123 comprising one or more load devices 124, 126) via the output node 104. According to a particular embodiment, the load 123 is resistor divider, and the first load device 124 has twice the resistance of the second load device 126. Other embodiments may stabilize frequency under other load conditions.
The drain 115 of the third transistor 116 may be coupled to a drain of the first transistor 110 to receive the bias current 134. The source of the third transistor 116 may also be coupled to a gate of the third transistor 116 via a connection 125. The third transistor 116 may be configured to form a diode configuration directing current flow from the gate of the third transistor 116 to the capacitor 120. The first transistor 110 and the third transistor 116 may form a gain stage 131. The gain stage 131 may include a gain based on a transconductance (gm) of the first transistor 110 divided by the transconductance of the third transistor 116 (Gain=gm110/gm116). According to a particular embodiment, the third transistor 116 may have a large length 130 and a small width 132 (where the length 130 and the width 132 correspond to channel dimensions). The third transistor 116 may be coupled to a ground node 118.
A loop gain of the voltage regulator 100 may include a product of a gain and a feedback factor of a feedback loop that includes the error amplifier 102, the output node 104, the feedback path 106, the voltage buffer 108, the first transistor 110, the second transistor 114, and the load 123. The loop gain may further include the output pole associated with the output node 104. The loop gain of the voltage regulator 100 may also include the zero associated with the capacitor 120 and the gain stage 131. In response to a change in the output current at the output node 104, a frequency value associated with the zero may change (e.g., in response to a larger output current). The zero may be adjusted to track or substantially track the output pole associated with the output node 104 to stabilize the voltage regulator 100.
According to a particular embodiment, the capacitor 120 may be a compensation capacitor used in combination with the third transistor 116 to adjust the zero. The zero may be adjusted to offset the output pole associated with the output node 104. The capacitor 120 may be coupled to the node 122 that is located between the error amplifier 102 and the voltage buffer 108. The gain stage 131 and the capacitor 120 may form a Miller capacitor. The Miller capacitor may increase an equivalent capacitance at the output of the error amplifier 102 and proximate to the node 122. The equivalent capacitance may equal the gain multiplied by the capacitance of the capacitor 120. The associated Miller effect may enable a large capacitance despite using a small capacitor. For example, the capacitor 120 may have a value of less than 300 picofarads (pF).
The Miller effect may further create a dominant pole, or lowest frequency pole, near the node 122. The dominant pole may be equal to the inverse of the product of the equivalent capacitance multiplied by an output resistance present at the output node 104. The dominant pole may at least partially cancel out a high frequency pole located near the output of the voltage buffer 108.
The Miller effect provided by the gain stage 131 and the capacitor 120 may further create the zero near the node 122. The zero may equal the inverse of the product of the capacitance of the capacitor 120 and a resistance of the third transistor 116. Put another way, the zero may equal the gain of the third transistor 116 divided by the capacitance of the capacitor 120. In so doing, the zero may track the remaining output pole to stabilize the voltage regulator 100.
The third transistor 116 may receive the bias current 134 from the first transistor 110. An increase in the bias current 134 may increase transconductance associated with the third transistor 116. Conversely, a decrease in the bias current 134 may decrease the transconductance associated with the third transistor 116. When a current load at the output node 104 causes the output pole to change positions, the transconductance associated with the third transistor 116 may be adjusted in response. For example, if a large current load at the output node 104 causes the output pole to change positions, the transconductance associated with the third transistor 116 may decrease. The decrease in the transconductance may cause a zero in the loop gain of the voltage regulator 100 to change position similarly and according to the output pole. The zero may offset the output pole to stabilize the voltage regulator 100.
The first voltage regulator 205 may be the same as the voltage regulator 100 of
A first transistor 210 may be coupled to an output of the voltage buffer 208. The first transistor 210 may be coupled to a voltage supply source VIN 260 and to a second transistor 214. The first transistor 210 may be configured to mirror the second transistor 214. The second transistor 214 may be coupled to the voltage supply source VIN 260, the output voltage VOUT 262, and the load 222.
A third transistor 216 may be coupled to a drain of the first transistor 210 and may be coupled to have a diode configuration. The first transistor 210 and the third transistor 216 may form a gain stage. A gate of the third transistor 216 may be coupled to a capacitor 220. According to a particular embodiment, the capacitor 220 may have a value of less than 300 pF. The third transistor 216 and the capacitor 220 may affect a zero that may be adjusted to track an output pole associated with the output voltage VOUT 262 to stabilize the first voltage regulator 205.
The second voltage regulator 207 may be the same as the first voltage regulator 205 and the voltage regulator 100 of
A first transistor 240 may be coupled to an output of the voltage buffer 238. The first transistor 240 may be coupled to a voltage supply source VIN 264 and to a second transistor 253. The first transistor 240 may be configured to mirror the second transistor 253. The second transistor 253 may be coupled to the voltage supply source VIN 264, the output voltage \lour 266, and the load 252. In a particular embodiment, the VIN 260 may be the same as the VIN 264, and the VOUT 262 may be the same as the VOUT 266. In another particular embodiment, the VIN 260 may be different than the VIN 264, the VOUT 262 may be different than the VOUT 266, or any combination thereof.
A third transistor 246 may be coupled to a drain of the first transistor 240 and may be coupled to have a diode configuration. The first transistor 240 and the third transistor 246 may form a gain stage. A gate of the third transistor 246 may be coupled to a capacitor 250. According to a particular embodiment, the capacitor 250 may have a value of less than 300 pF. The third transistor 246 and the capacitor 250 may affect a zero that may be adjusted to track an output pole associated with the output voltage VOUT 266 to stabilize the second voltage regulator 207.
At 302, an unregulated voltage may be received at a first transistor and at a second transistor. In a particular embodiment, the second transistor is a thin-oxide transistor. For example, the unregulated voltage from the voltage supply source VIN 128 of
A third transistor may be biased based on a bias current from the first transistor, at 304. The first transistor and the second transistor are responsive to an error voltage generated by an error amplifier that is responsive to a reference voltage and to an output node of a voltage regulator via a feedback path. The third transistor may comprise a diode configuration. For instance, the third transistor 116 of
A transconductance associated with the third transistor may be increased in response to an increase in the bias current, at 306. For example, the transconductance associated with the third transistor 116 of
In response to a change in an output current, a zero associated with the third transistor and with a capacitor may track an output pole associated with the output node, at 308. The capacitor may be coupled to the error amplifier and the third transistor. For instance, a zero associated with the third transistor 116 and the capacitor 120 of
Referring to
In conjunction with the described embodiments, an apparatus is disclosed that includes a means for amplifying an error, such as the error amplifier 102 of
In conjunction with the described embodiments, method of regulating voltage is disclosed that includes a step for receiving an unregulated voltage at a first transistor and at a second transistor and a step for biasing a third transistor based on a bias current from the first transistor. The first transistor and the second transistor may be responsive to an error voltage generated by an error amplifier that is responsive to a reference voltage and to an output node of a voltage regulator via a feedback path.
The foregoing disclosed devices and functionalities may be designed and configured into computer files (e.g. RTL, GDSII, GERBER, etc.) stored on computer readable media. Some or all such files may be provided to fabrication handlers who fabricate devices based on such files. Resulting products include semiconductor wafers that are then cut into semiconductor die and packaged into a semiconductor chip. The chips are then employed in devices described above.
Physical device information 502 is received in the manufacturing process 500, such as at a research computer 506. The physical device information 502 may include design information representing at least one physical property of a semiconductor device, such as the voltage regulator 100 of
In a particular embodiment, the library file 512 includes at least one data file including transformed design information. For example, the library file 512 may include a library of semiconductor devices including the voltage regulator 100 of
The library file 512 may be used in conjunction with the EDA tool 520 at a design computer 514 including a processor 516, such as one or more processing cores, coupled, to a memory 518. The EDA tool 520 may be stored as processor executable instructions at the memory 518 to enable a user of the design computer 514 to design a circuit using the voltage regulator 100 of
The design computer 514 may be configured to transform the design information, including the circuit design information 522 to comply with a file format. To illustrate, file formation may include a database binary file format representing planar geometric shapes, text labels, and other information about a circuit layout in a hierarchical format, such as a Graphic Data System (GDSII) file format. The design computer 514 may be configured to generate a data file including the transformed design information, such as a GDSII file 526 that includes information describing the voltage regulator 100 of
The GDSII file 526 may be received at a fabrication process 528 to manufacture the voltage regulator 100 of
The die 536 may be provided to a packaging process 538 where the die 536 is incorporated into a representative package 540. For example, the package 540 may include the single die 536 or multiple dies, such as a system-in-package (SiP) arrangement. The package 540 may be configured to conform to one or more standards or specifications, such as Joint Electron Device Engineering Council (JEDEC) standards.
Information regarding the package 540 may be distributed to various product designers, such as via a component library stored at a computer 546. The computer 546 may include a processor 548, such as one or more processing cores, coupled to a memory 510. A printed circuit board (PCB) tool may be stored as processor executable instructions at the memory 550 to process PCB design information 542 received from a user of the computer 546 via a user interface 544. The PCB design information 542 may include physical positioning information of a packaged semiconductor device on a circuit board, the packaged semiconductor device corresponding to the package 540 including the voltage regulator 100 of
The computer 546 may be configured to transform the PCB design information 542 to generate a data file, such as a GERBER file 552 with data that includes physical positioning information of a packaged semiconductor device on a circuit board, as well as layout of electrical connections such as traces and vias, where the packaged semiconductor device corresponds to the package 540 including the voltage regulator 100 of
The GERBER file 552 may be received at a board assembly process 554 and used to create PCBs, such as a representative PCB 556, manufactured in accordance with the design information stored within the GERBER file 552. For example, the GERBER file 552 may be uploaded to one or more machines for performing various steps of a PCB production process. The PCB 556 may be populated with electronic components including the package 540 to form a represented printed circuit assembly (PCA) 558.
The PCA 558 may be received at a product manufacture process 560 and integrated into one or more electronic devices, such as a first representative electronic device 562 and a second representative electronic device 564. As an illustrative, non-limiting example, the first representative electronic device 562, the second representative electronic device 564, or both, may be selected from the group of a set top box, a music player, a video player, an entertainment unit, a navigation device, a communications device, a personal digital assistant (PDA), a fixed location data unit, and a computer. As another illustrative, non-limiting example, one or more of the electronic devices 562 and 564 may be remote units such as mobile phones, hand-held personal communication systems (PCS) units, portable data units such as personal data assistants, global positioning system (GPS) enabled devices, navigation devices, fixed location data units such as meter reading equipment, or other devices that store or retrieve data or computer instructions, or a combination thereof. Although one or more of
Thus, the voltage regulator 100 of
Those of skill would further appreciate that the various illustrative logical blocks, configurations, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. Various illustrative components, blocks, configurations, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disk, a removable disk, a compact disc read-only memory (CD-ROM), or a other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an application-specific integrated circuit (ASIC). The ASIC may reside in a computing device or a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a computing device or user terminal.
The previous description of the disclosed embodiments is provided to enable a person skilled in the art to make or use the disclosed embodiments. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the principles defined herein may be applied to other embodiments without departing from the scope of the disclosure. Thus, the present disclosure is not intended to be limited, to the embodiments shown herein but is to be accorded, the widest scope possible consistent with the principles and novel features as defined by the following claims.
