Amplifiers – With semiconductor amplifying device – Including class d amplifier
Reexamination Certificate
2002-01-15
2003-04-22
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including class d amplifier
C330S20700P, C330S302000
Reexamination Certificate
active
06552610
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to amplifiers and, more particularly, to a tuned switching power amplifier.
BACKGROUND OF THE INVENTION
Amplifiers are commonly used to increase the strength of electrical signals. To increase the strength of an electrical signal, typically, the electrical signal is used to control a flow of energy from a DC power source, e.g., a battery, to produce an output signal that varies in the same way as the electrical signal but has a larger amplitude. Generally, it is desirable to efficiently amplify the electrical signal using a minimal amount of power to reduce energy costs and increase battery life, for example.
One method for efficiently amplifying electrical signals is disclosed in U.S. Pat. No. 3,919,656 to Sokal et al., entitled High-Efficiency Tuned Switching Power Amplifier, incorporated fully herein by reference. Additionally, U.S. Pat. No. 3,919,656 contains a detailed discussion of power amplifiers.
FIG. 1
is a circuit diagram of a tuned switching power amplifier
100
as disclosed in U.S. Pat. No. 3,919,656. The amplifier
100
includes a switch
102
responsive to an input signal from a signal source
104
, a DC power source
106
, and a load network
108
to create a transient response across the switch
102
and pass an amplified version of the input signal to a load
110
. In operation, the switch
102
controls the flow of current from the DC power source
106
based on the input signal to generate an output signal at the load
110
having a greater amplitude than the input signal at the same frequency. The operating frequency of the amplifier
100
is its fundamental frequency.
In the amplifier
100
, power may be wasted by the switch
102
in the form of heat when current is flowing through the switch
102
at the same time there is a voltage drop across the switch
102
. Accordingly, to increase efficiency, the amplifier
100
is designed to: a) minimize the voltage across the switch
102
when appreciable current flows through it; b) minimize the current flowing through the switch
102
when appreciable voltage exists across it; and c) minimize the duration of simultaneous appreciable voltage across the switch
102
and current through the switch
102
.
The load network
108
functions to produce a transient response across the switch
102
that satisfies the above design conditions. The load network
108
includes a current feed choke
112
, a bypass capacitor
114
, a parallel capacitor
116
, a frequency filter
118
, and a series inductor
120
. The current feed choke
112
may be a quarter-wave transmission line (TL), i.e., a TL having an electrical length of 90° in reference to the fundamental frequency, with negligibly small inductive susceptance for supplying essentially a constant current during the operation of the amplifier
100
. If the inductive susceptance of the current feed choke
112
is not negligibly small, the capacitance of the parallel capacitor
116
is increased, thereby increasing the susceptance of a path containing the parallel capacitor
116
and effectively removing the current feed choke
112
from the amplifier
100
at the fundamental frequency. The frequency filter
118
includes a capacitor
122
and an inductor
124
, and is designed so that only signals at the fundamental frequency are allowed to pass through the frequency filter
118
, i.e., the frequency filter
118
is tuned to the fundamental frequency.
FIG. 2
illustrates the impedance as seen by the switch
102
at the fundamental frequency. At the fundamental frequency, the current feed choke
112
acts as an infinite impedance and the frequency filter
118
acts as a short. Therefore, the resultant impedance seen by the switch
102
can be represented by the parallel capacitor
116
, the series inductor
120
, and the impedance of the load
110
. Accordingly, the parallel capacitor
116
and the series inductor
120
are the primary elements for producing a desired transient response across the switch
102
.
Often, the size of an amplifier
100
is an important criteria depending on the application for which the amplifier
100
will be used. If an amplifier
100
having a small form factor is desired, a current feed choke
112
implemented using a TL with an electrical length of 90° may inhibit a reduction in the size of the amplifier. In addition, the series inductor
120
may adversely contribute to the size of the amplifier
100
and in conjunction with the parallel capacitor
116
may produce an undesirable impedance transformation at the output of the amplifier
100
. Accordingly, there is a need for an efficient tuned switching power amplifier having less series inductance and a parallel TL with an electrical length of less than 90°. The present invention fulfills this need among others.
SUMMARY OF THE INVENTION
The present invention provides for a switching tuned power amplifier apparatus and method that overcomes the aforementioned problems by placing a parallel capacitor and a parallel TL having an electrical length of less than 90° across a switch within the amplifier. The parallel capacitor and parallel TL create a transient response across the switch that minimizes current and voltage existing across the switch simultaneously. By using a capacitor and a TL having an electrical length of less than 90° in parallel across the switch, efficient tuned switching power amplifiers having smaller form factors and desirable impedance transformation can be realized.
One aspect of the present invention is a switching amplifier apparatus for amplifying an input signal having a fundamental frequency to develop an output signal with the same frequency at a load. The amplifier includes a switch having a control for receiving the input signal, the switch responsive to the input signal to turn the switch on and off, the switch further having first and second terminals, the first and second terminals having a low impedance therebetween when the switch is on and having a high impedance therebetween when the switch is off, a load network coupled to the switch to deliver the output signal to the load, the load network including a TL of a determined length coupled between the first and second terminals to develop a parallel inductance across the switch and a parallel capacitor coupled between the first and second terminals to develop a parallel capacitance across the switch, a DC power source for supplying DC power to the TL, the parallel capacitor, and the switch. The TL and the parallel capacitor create a transient response across the switch that insures that, as the switch transitions from on to off, the voltage across the first and second terminals remains low until the current through the first and second terminals is substantially zero, and, prior to the switch's transition from off to on, the voltage across the first and second terminals and the voltage time derivative are substantially zero.
Another aspect of the invention is a method for amplifying an input signal having a fundamental frequency to develop an output signal with the same frequency at a load. The method includes applying the input signal to a switch responsive thereto, developing parallel inductance across the switch with a TL of a determined length, developing parallel capacitance across the switch, supplying DC voltage to the switch, the parallel inductance, and the parallel capacitance, wherein the parallel inductance and capacitance develop a transient response across the switch to insure the voltage across the switch remains low, as the switch transitions from on to off, until the current through the switch is substantially zero, and the voltage across the switch and the voltage time derivative are substantially zero prior to the switch's transition from off to on.
REFERENCES:
patent: 3919656 (1975-11-01), Sokal et al.
patent: 5434540 (1995-07-01), Yamamoto et al.
patent: 6181208 (2001-01-01), King et al.
patent: 6236274 (2001-05-01), Liu
V. B. Kozyrev, “Single-Ended Switching-Mode Tuned Power Amplifier with Filtering Circuit” (in Russ
Grebennikov Andrei Viktorovich
Jaeger Herbert
Choe Henry
MVA.com Eurotec, B.V.
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