Amplifiers – With semiconductor amplifying device – Including particular power supply circuitry
Reexamination Certificate
2000-08-14
2002-04-16
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including particular power supply circuitry
C330S051000
Reexamination Certificate
active
06373340
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to power amplifiers in general, and, more particularly, to high-efficiency audio power amplifiers, especially for battery-operated applications.
BACKGROUND OF THE INVENTION
A major problem associated with power amplifiers is inefficient use of electrical energy. Especially for audio applications, and more specifically in battery-operated portable audio applications, improving the efficiency of the power amplifier has major benefits in terms of performance as well as cost.
Most of the inefficiency of power amplifiers is a result of power dissipated within the power stage. The dissipated power is a function of the difference between the supply voltage and the output voltage of the power stage. In applications such as audio, where the peak-to-RMS ratio is high (about 12 dB), the peak dictates the supply voltage, but, most of the time the output voltage is significantly lower, and thus a significant amount of power is dissipated in the power stage.
Power dissipation (typical to class-A, AB, B, C, D, and Pulse Width Modulation (PWM), and/or output-of-band noise energy (typical to class D and PWM), is the main cause of inefficiency in prior art power amplifiers, and results in excessive electrical power consumption. The heat developed in the power stage must be dissipated, and the need to provide for adequate heat removal impacts the design and performance of integrated circuit components, and requires design compromises and special engineering expertise.
Further limiting factors associated with prior art power amplifies include limitations in their dynamic range (limited by the power-supply voltage), and their inability to achieve output over the full supply voltage range (“rail-to-rail” operation). Moreover, additional major problems in the design of existing power amplifiers include non-linearity and noise.
When designing a power amplifier, these factors—efficiency, linearity, dynamic range, and freedom from noise—conflict with one another, and optimizing the design to overcome one will compromise the design's ability to overcome the others.
It is already known in the art that by employing a tracking power-supply which minimizes the difference between the power-supply voltage provided to the power stage and the required output voltage of the power stage, that the dissipated power may be minimized. The minimizing action of a track power-supply is herein denoted by the terms “track” and “tracking”, and is effected by providing a target function for determining the output of the tracking power-supply. The arguments of the target function may include the input signal to the power amplifier as well as the internal input to the power stage. There are, however, difficulties in implementing a tracking power-supply that is in itself efficient and suitable for a given application. For example, in the prior art are known tracking power-supplies which are based on switched L-C circuits. Because L-C circuits are reactive and store rather than dissipate energy, such tracking power-supplies are efficient. Unfortunately, the inductors of L-C circuits are not suitable for use with integrated circuits, and therefore such prior-art tracking power-supplies are not useful in applications involving miniaturized and/or battery-operated equipment.
There is thus a widely recognized need for, and it would be highly advantageous to have, a high-efficiency power amplifier with linear response, low noise, and with a wide dynamic range. These goals are met by the present invention.
REFERENCES
[1] EP0998795, WO9905806 “Method and apparatus for performance improvement by qualifying pulses in an oversampled, noise-shaping signal process”
[2] EP0906659, WO09749175 “Oversampled, noise-shaping, mixed-signal processor”
[3] “Relationships between Noise Shaping and Nested Differentiating Feedback Loops”, by J. Vanderkooy, and M. O. J. Hawksford,
Journal of the Audio Engineering Society,
Vol. 47, No. 12, December 1999.
TERMS AND DEFINITIONS
Tracking Power-Supply—A power-supply capable of providing a variable output voltage to suit the needs of a power amplifier. According to the present invention, an efficient tracking power-supply is implemented, having control logic controlling a network of switched capacitors. By controlling the switches, different network connections can be made, giving rise to different electrical circuits. This allows creating multiple supply voltages with high efficiency at the load terminals, and monitoring voltages through the sensor terminals.
Multi-Level Quantizer—The above tracking power-supply can be viewed as a quantizer (a “multi-level quantizer”) with multiple output levels possible during different time intervals, where the level changes during each time interval according to the voltages on the capacitors.
Network of Switched Capacitors—the network of switches and capacitors used in the tracking power-supply.
Network Connection—This is a specific set of connections, created by controlling the switches of the network of switched capacitors. This set of network connections creates an electrical circuit involving some or all of the capacitors, supplies, load terminals and sensor terminals.
Network State—The state of the network of switched capacitors at a certain time. The voltages across the capacitors define the network state.
I-Bit State—a specific case of a network state where a 1-bit state per capacitor indicates whether the voltage over it is higher or lower than some target voltage. This is useful when implementing the target capacitors selection algorithm.
Sensor—A sensor is any means of monitoring the network state while causing minimal affect. To monitor voltage over a certain capacitor, an appropriate network connection can be made by the control logic. A sensor for the 1-bit state can be the output of a comparator, comparing the voltage over the capacitor to the target voltage.
Estimated Network State—An estimated network state is a network state where some or all of the capacitor voltages are estimated rather than directly monitored.
Network Parameters—The network parameters include sufficient information about components involved in the work of switched capacitors. By way of example, this information may include electrical parameters of the load and main supplies, the capacitance of each capacitor, and the time intervals, whether absolute or relative. In certain embodiments of this invention, the control logic may need to known network parameters in order to estimates, or predict, the estimated network state when direct monitoring is not feasible. The network parameters may be supplied to the control logic, or may be measured by the control logic through the sensor, whether during initialization time, during operation, or both.
Time Interval—A period of time during which the network connection is held fixed. The duration of such time intervals may be constant or variable, depending on the application.
Load Time Interval—A time interval during which the network connection involves the tracking power-supply output terminals.
Monitoring Time Interval—A time interval during which monitoring of the network state can be performed. A monitoring time interval can overlap a load time interval.
Control Logic—Logic controlling the network of switched capacitors via the switches, in order to create a desired network connection. The main task of the control logic is to determine the best network connection involving the load at any time interval. The control logic implements a selection algorithm, and attempts to minimize the value of the target function, while conforming to some other criteria. The control logic may be implemented fully in the digital domain, while monitoring the state of the network of switched capacitors through the sensor. Alternatively, the control logic can be implemented in the analog domain. The control logic unit has one or more inputs and one or more control outputs.
Target Function—At each load time interval, there is an ideal desired output from the track power-supply.
Fitch Even Tabin & Flannery
K. S. Waves Ltd.
Nguyen Khanh Van
Pascal Robert
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