Patent Application
20070210775
This invention relates generally to power supplies and specifically to power supply integration for low-power single chip RF CMOS solutions.
Battery-operated electronics typically contain circuits that require different supply voltages. Battery voltage is typically changed to meet supply voltage requirements of a phase-locked loop with either voltage regulators or direct-current to direct-current (DC-to-DC) converters.
Voltage regulator 100 use with a battery 114 in a battery-powered device is inefficient. For example, if Vin=3.3 vdc, Vout=1.8 vdc, and Ireg<<<Iout so that Iout≈Iin, then maximum voltage regulator efficiency=54.5%. Thus, in a battery-powered device, excess energy is wasted as heat and tends to drain a battery 114 at a quick rate.
As illustrated in
Accordingly, what is needed is an invention that overcomes the shortcomings noted above.
A method and apparatus for converting and regulating DC power at high-efficiency with low noise. Power is supplied to a DC-to-DC converter, the output of which feeds a low-dropout voltage regulator. A DC-to-DC converter efficiently performs voltage conversion while a low-dropout voltage regulator rejects noise and regulates an output voltage.
Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.
In the drawings:
Embodiments of the present invention provide a method and apparatus for power supply integration for low-power single chip RF CMOS circuits.
Exemplary Structure
Referring to
A DC-to-DC converter 322 is used to convert an input DC voltage to an output DC voltage that is different from the input DC voltage. Thus, DC-to-DC converters are used to step-up or step-down a DC voltage. An output DC voltage of a DC-to-DC converter 322 may be lower than an input voltage of the DC-to-DC converter. However, an output DC voltage of a DC-to-DC converter 322 may also be higher than an input voltage of the DC-to-DC converter. In an example, a DC-to-DC converter 322 has a supplied voltage (V1) 308 in an inclusive range from 1.0 VDC through 1.6 VDC and an intermediate voltage (V2) 306 output of 1.8 VDC.
In one example, a DC-to-DC converter 322 is coupled to a ground 106. In one embodiment, a DC-to-DC converter 322 is configured to have an efficiency over seventy percent. Use of a DC-to-DC converter 322 with an efficiency of over ninety percent is preferred. In one embodiment of the invention, a DC-to-DC converter 322 is Torex part number XC9216A20CMR that is available from Torex Corporation, located at 3 Corporate Park, Suite 270; Irvine, Calif. 92606.
An output of a DC-to-DC converter 322 is coupled to an input of a low-dropout voltage regulator 304. A voltage regulator such as a low-dropout voltage regulator 304 maintains a substantially constant output voltage when the voltage regulator's input voltage varies. The output voltage of the voltage regulator is also substantially stable for variation in loads coupled to the voltage regulator's output.
Dropout voltage is a differential voltage between a voltage input to a voltage regulator, for example intermediate voltage (V2) 306, and a voltage output from the voltage regulator, for example output voltage (V3) 316. The low-dropout voltage regulator 304 has a small dropout voltage relative to a dropout voltage of a typical voltage regulator 100. A dropout voltage of a low-dropout voltage regulator 304 is less than 20% of an intermediate voltage (V2) 306 input to the low-dropout voltage regulator 304. In one example, for an input intermediate voltage (V2) 306 voltage of 2.0 VDC, a dropout voltage is approximately 0.1 VDC. In one example, a dropout voltage is equal to or less than one-hundred millivolts. The low-dropout voltage regulator 304 also has a power supply rejection ratio (PSRR) of greater than forty decibels in example embodiments of the invention. In one example, a low-dropout voltage regulator 304 is coupled to ground 106.
In the power integration system 302 shown in
The invention has many applications. In one example, an output of a low-dropout voltage regulator 304 is coupled to a circuit comprising a PLL 324. In another example, an output of a low-dropout voltage regulator 304 is coupled to a circuit comprising a noise-sensitive load. A noise-sensitive load is, for example, a load that provides degraded performance when powered by a noisy power supply. The invention may be part of a single-chip radio frequency circuit or a communication circuit. In other examples, a low-dropout voltage regulator 304 output supplies power to a memory circuit, a processor, a logic circuit, and/or other circuits.
The high-efficiency DC-to-DC converter 322, low-dropout voltage regulator 304, and PLL 324 may be comprised of complementary metal oxide semiconductors. The high-efficiency DC-to-DC converter 322, low-dropout voltage regulator 304, and PLL 324 may also be comprised of any combination of discrete and integrated components. In one example, the high-efficiency DC-to-DC converter 322, low-dropout voltage regulator 304, and PLL 324 are deposited on a common substrate. In addition to other benefits, deposition on a common substrate reduces manufacturing cost and saves space.
Exemplary Method of Operation
In step 402, an input power supply voltage is received. The input power supply voltage is typically un-regulated and is a source power supply that is desired to be converted to one or more regulated power supplies that are lower in voltage.
In step 404, an input power supply voltage is efficiently converted to an intermediate voltage. In an example, the input power supply voltage is a higher magnitude voltage than the intermediate voltage. In another example, a power supply 302 provides power to an input of the DC-to-DC converter 322. For example, a power supply 302 may be a 3.3 VDC battery. The DC-to-DC converter 322 converts the supplied voltage (V1) 308 and supplied current (I1) 310 to an intermediate voltage (V2) 306 and intermediate current (I2) 312. The intermediate voltage (V2) 306, for example, is smaller in magnitude than the supplied voltage (V1) 308. Excess energy is shunted to ground 106 by the DC-to-DC converter 322 in the form of IDCDC 314. The efficiency of the DC-to-DC converter 322 is defined as the (V2 306·I2 312)/(V1 308·I1 310). The DC-to-DC converter 322 efficiency should be greater than eighty percent and is preferably greater than ninety percent. The output of the DC-to-DC converter 322 provides an input to the low-dropout voltage regulator 304.
In step 406, the low-dropout voltage regulator 304 regulates the output voltage (V3) 316 at the output of the low-dropout voltage regulator 304 and shunts excess energy to ground 106 in the form of a voltage regulator current (Ivr) 318. The output voltage (V3) 316 is derived from the intermediate voltage (V2) 306. For example, if the low-dropout voltage regulator 304 input intermediate voltage (V2) 306 is 1.85 volts DC or greater, then the low-dropout voltage regulator 304 output voltage (V3) 316 is a regulated voltage output of approximately 1.8 volts DC.
While regulating in step 406, a low-dropout voltage regulator 304 also simultaneously rejects noise present at the low-dropout voltage regulator 304 input. Part of this noise is typically present as a result of DC-to-DC converter 322 operation. For example, a low-dropout voltage regulator 304 rejects eight decibels of noise. Preferably, the low-dropout voltage regulator 304 should have a power supply rejection ratio (PSRR) of greater than thirty decibels. More preferably, a low-dropout voltage regulator 304 has a PSRR of greater than forty decibels. The low-dropout voltage regulator 304 should also reject at least five decibels of noise below 30 KHz. Preferably, a low-dropout voltage regulator 304 that rejects at least five decibels of noise below 30 KHz is used to power a PLL 324, with loop bandwidth>100 Khz to increase the response time and reduce the size of the PLL 324. Thus, the low-dropout voltage regulator 304 supplies power with a minimum amount of low frequency noise.
In an example, the low-dropout voltage regulator 304 rejects noise below a sensitive frequency of a load. The sensitive frequency of a load is a threshold frequency of noise present in the load's power supply above or below which the load's performance becomes degraded.
The low-dropout voltage regulator 304 is of a low-dropout voltage design to provide high efficiency. Use of a low-dropout voltage regulator 304 with a dropout voltage of less than one-hundred millivolts is preferred. Ideally, (V3) 316 should equal (V2) 306. The low-dropout voltage regulator 304 operates with high efficiency in part because the difference between voltage regulator input intermediate voltage (V2) 306 and output voltage (V3) 316 is small. With a large input to output voltage differential, for example when V2 306>>V3 316, a low-dropout voltage regulator 304 typically achieves low efficiency. By using a very small input to output voltage differential, a low-dropout voltage regulator 304 can achieve an efficiency greater than at least ninety percent.
Thus, the overall efficiency of the combination of the DC-to-DC converter 322 and the low-dropout voltage regulator 304 is high because both the DC-to-DC converter 322 and the low-dropout voltage regulator 304 operate very efficiently. The combination of the DC-to-DC converter 322 and the low-dropout voltage regulator 304 also simultaneously produce a low-noise output. When low-dropout voltage regulator output current is denoted by (I3) 320, the combined efficiency is given by: Efficiency=(V3 316·I3 320)/(V1 308·I1 310)=((V3 316·I3 320)/(V2 306·I2 312))·((V2 306·I2 312)/(V1 308·I1 310)). For example, if V1=3.3 vdc, V3=1.8 vdc, V2=1.85 vdc, Ireg<<<Iout, and DC-to-DC converter 322 efficiency is 85%, then a combined efficiency of (97%)·(85%)=82.4% can be achieved. Thus, the combined efficiency in this example is an improvement over the 54.5% efficiency of the voltage regulator 100 used alone as shown in
In another embodiment shown in
Power from the low-dropout voltage regulator 304 can be supplied to many different types of loads including but not limited to PLLs 324, oscillators, memory circuits, processors, audio codecs, and other circuits. Other applications include but are not limited to powering transmitters, receivers, transceivers, and telecommunication headsets.
Conclusion
Example embodiments of the methods, systems, and components of the present invention have been described herein. As noted elsewhere, these example embodiments have been described for illustrative purposes only, and are not limiting. Other embodiments are possible and are covered by the invention. Such other embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
It is to be appreciated that the Detailed Description section, and not the Summary or Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus are not intended to limit the present invention and the appended claims in any way.
