1. Field of the Invention
The present invention relates to a low-voltage current reference, and more particularly, a low-voltage current reference providing a current being substantially constant with temperature.
2. Description of the Prior Art
Prior power references—current references and voltage references, for example—are subject to variances with temperature, affecting the performance of the circuits being powered by them. Many timers and other high-accuracy circuits and chips, however, require current references that are insensitive to fluctuations in temperature.
A bandgap reference is a common analog circuit used as a stable voltage reference for low-voltage circuits. In normal practice, as shown in
There are, however, a number of problems and inconveniences from the above. The bandgaps 120 and 140 take up significant real estate on a circuit, and consume considerable power themselves. Additionally, each of the above bandgaps 120 and 140 requires a start circuit (115 and 110, respectively) to ensure they operate properly and in a timely fashion. These start circuits 115 and 110 occupy circuitry real estate and also consume power. From these issues, then, it becomes clear there remains room for improvement in the arena of temperature-insensitive current sources.
It is therefore an objective of the present invention to solve the aforementioned problems, and to provide a low-voltage current reference providing a current being constant with temperature while reducing the power and circuit area consumed by the low-voltage current reference.
In one embodiment of the present invention, a low-voltage current reference providing a current being substantially constant with temperature comprises a low voltage bandgap, a start circuit coupled to the low voltage bandgap, and a current summer coupled to the low voltage bandgap and to the start circuit. The low voltage bandgap is for providing a constant voltage reference to be applied across a resistor, and the start circuit is for starting the low voltage bandgap from a non-start mode and for providing a proportional to absolute temperature (PTAT) current reference. The current summer is for providing a constant current reference according to the CTAT current (e.g., Icmnres) and the PTAT current reference (e.g., Iptat).
In another embodiment of the present invention, a method for providing a low-voltage current reference being substantially constant with temperature comprises providing a constant voltage reference utilizing a low voltage bandgap, starting the low voltage bandgap from a non-start mode and providing a PTAT current reference by utilizing a start circuit coupled to the low voltage bandgap, and generating a constant current reference according to the constant voltage reference and the PTAT current reference by utilizing a current summer coupled to the low voltage bandgap and to the start circuit.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by advantageous embodiments of the present invention, which include certain circuits and schematics of the components described within the disclosure of the present invention.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and descriptions of the present invention will be described hereinafter which form the subject of the claims of the present invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.
Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” The terms “coupled” and “couples” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
As mentioned, an objective of the present invention is to provide a low-voltage current reference providing a current being substantially constant with temperature, while reducing the power and circuit area consumed by the low-voltage current reference.
Please refer to
The low voltage current reference 200 of
Of particular note in
Although the schematic diagram in
Turning to the start circuit,
Please note that the schematic diagram in
With a voltage input from the first voltage node Va as the negative input to the second op amp opamp2 and the positive feedback loop provided from the second voltage node Vd, the start circuit 210 generates an output PTAT current Iptat (also shown in
By employing the above embodiments, or other variations that would be clear to a person skilled in the art after reading the above disclosure, the present invention generates a constant with temperature current reference Iconst utilizing a single start circuit 210, one low voltage bandgap 220, and a current summer 230. By removing the necessity of a (second) PTAT current bandgap 140 and a second start circuit 115, the required circuit and layout real estate is reduced. The present invention also enjoys the benefits of greatly reduced power consumption and lower circuit complexity, while retaining high performance and accuracy.
Please refer to
Step 510: Generate a constant voltage reference utilizing a low voltage bandgap.
Step 520: Start the low voltage bandgap from a non-start mode utilizing a start circuit.
Step 530: Generate a proportional to absolute temperature (PTAT) current reference utilizing the start circuit.
Step 540: Generate a constant current reference according to the constant voltage reference applied across a resistor (i.e., Icmnres) and the PTAT current reference (i.e., Iptat) utilizing a current summer.
As shown in
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, many of the processes discussed above can be implemented in different methodologies and replaced by other processes, or a combination thereof.
For example, in one embodiment of a method according to the present invention, another step is included for selecting values of at least the first resistor R3 and the first diode Q1 connected in series in the low voltage bandgap 220 (for example), such that the current flowing through the first resistor R3 and the first diode Q1 is an internal PTAT current, the first internal PTAT current Iptat_internal1.
In yet another embodiment, a further step (not shown) involves matching a second internal PTAT current Iptat_internal2 within the start circuit 210 to the first internal PTAT current Iptat_internal1 by selecting values of at least the second resistor Rd and the second diode Qd connected in series in the start circuit 210, where one end of the second resistor Rd is connected to the second diode Qd and the other end of the second resistor Rd is coupled to a second voltage node (Vd in
It should be noted that although the embodiments of the present invention have been mentioned in use for high-accuracy circuits and chips, the application to high-accuracy or sensitive electronic circuits is not a limitation of the scope of this invention. The present invention can be applied to any electronic circuits and such applications and embodiments also obey the spirit of and should be considered with the scope of the present invention.
After reviewing this first embodiment of the present invention, other applications and implementations will be obvious to those skilled in the art, and should be included within the scope of the present invention. Similar applications encompassed and alluded to by the present invention for reducing the number of components (such as the start circuit 115 and the PTAT current bandgap 140) should also be considered inside the scope of the present invention.
Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.
Number | Name | Date | Kind |
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6191646 | Shin | Feb 2001 | B1 |
20060279270 | Chen et al. | Dec 2006 | A1 |
20080018319 | Chang et al. | Jan 2008 | A1 |
Number | Date | Country | |
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20090261801 A1 | Oct 2009 | US |