Coded data generation or conversion – Analog to or from digital conversion – Differential encoder and/or decoder
Reexamination Certificate
2002-12-09
2004-07-13
Jeanglaude, Jean Bruner (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Differential encoder and/or decoder
C341S144000, C341S155000
Reexamination Certificate
active
06762704
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to the field of signal processing, and, more specifically, to a system and method for modulating an input signal with multiple digital signal modulators.
2. Description of the Related Art
Analog and digital modulators are utilized to convert analog and digital input signals into drive signals. For example, the modulators convert an input signal into discrete pulses using well-known pulse width modulation techniques. The pulses are used as drive signals. The drive signals are utilized to drive output current to a load. In an acoustic application, voice signals may be modulated to drive a load, such as audio speakers.
Power converters may be used to convert direct current (DC) to alternating current (AC) to be used as an AC power supply, or as battery chargers/dischargers, motor controls, etc. Power converters may also be used as amplifiers, both for entertainment (sound amplification) and industrial uses. Many conventional pulse width modulated (PWM) converters use a pair of switches to connect a load alternatively to DC power supplies of opposite polarity. A modulator alternately opens and closes the switches to produce a width modulated output signal that is subsequently filtered by a low pass filter before being transmitted to the load. Care must be taken to assure that both switches are not turned “on” at the same time to prevent drawing transient “shoot-through” current. Several means are used to limit or prevent such shoot-through current. For example, Current limiting inductors may be employed or “underlap” circuits may be used to create small controlled time gaps between the conduction times of the switches. Opening and closing the switches creates a generally undesirable “ripple” frequency on an output waveform generated by the conventional modulator.
Opposed current converters (“OCCs”) address the problem of ripple frequency generation. U.S. Pat. No. 5,657,219 entitled “Opposed Current Power Converter” by Gerald R. Stanley (referred to herein as the “Stanley Patent”) discloses an example of an OCC. Stanley and Bradshaw,
Precision DC
-
to
-
AC Power Conversion by Optimization of the Output Current Waveform—The Half bridge Revisited
, IEEE Transactions on Power Electronics, Vol. 14, No. 2, Mar. 1999 provide additional discussion. Opposed current converters (“OCCs”), which include amplifiers referred to as class-I amplifiers, opposed current amplifiers, balanced current amplifiers, and opposed current interleaved amplifiers, are particularly useful in audio applications due to their high efficiency and high signal to noise ratios in frequency bandwidths of interest.
Referring to
FIG. 1
, the Stanley Patent discloses a power converter circuit
100
, which is also sometimes referred to as an opposed current amplifier stage and is one embodiment of an OCC. Power converter circuit
100
receives two input drive signals S
p
′ and S
n
′. Signals S
p
′ and S
n
′ are square-waves with pulse-widths that are determined by modulating an input signal.
Power converter circuit
100
has four states of operation in the continuous current mode. Signals S
p
′ and S
n
′ determine the states of operation by respectively controlling the conductivity of switches
102
and
104
. Switches
102
and
104
conduct during the interval when S
p
′ and S
n
′ are both HIGH causing the main output inductor currents Ip and In to increase at a rate of approximately V/L, in which L=Lp=Ln and V is the magnitude of each supply voltage (Vsupply). When S
p
′ and S
n
′ are both HIGH, the magnetization of inductors Lp and Ln are increased. When S
p
′ and S
n
′ are both LOW, switches
102
and
104
become nonconductive, the inductor voltages are reversed, the diodes
108
and
110
conduct, and the inductor current magnitudes ramp down at the same rate. When S
p
′ and S
n
′ are both LOW, the magnetization of inductors Lp and Ln are decreased. When S
p
′ is LOW and S
n
′ is HIGH, switch
104
and diode
110
conduct resulting in negative output current (Iout) into output node
106
. When S
p
′ is HIGH and S
n
′ is LOW, switch
102
and diode
108
conduct resulting in positive output current Iout from node
106
.
Table 1 summarizes the four continuous current mode states of operation for power converter circuit
100
with reference to signals S
p
′ and S
n
′. Table 1 uses “HIGH” and “LOW” to represent the states of signals S
p
′ and S
n
′. In the embodiment of
FIG. 1
, a HIGH signal causes switches
102
and
104
to conduct, and a LOW signal causes switches
102
and
104
to open.
TABLE 1
Power Converter Circuit
S
p
′
S
n
′
100 Current Mode States
LOW
LOW
Demagnetizing
LOW
HIGH
Negative Output Current
HIGH
LOW
Positive Output Current
HIGH
HIGH
Magnetizing
Referring to
FIG. 2A
, the Stanley Patent describes an analog modulator
200
utilized to produce signals S
p
′ and S
n
′ for driving power converter circuit
100
. Analog modulator
200
utilizes an error amplifier
202
to generate an error signal
204
from an input signal
206
, representing a desired level at output node
106
of power converter circuit
100
, and a feedback signal
208
taken from output node
106
. Inverter
218
inverts error signal
204
to generate inverse error signal
216
. Comparators
210
and
214
generate respective signals S
p
′ and S
n
′ by comparing a triangle waveform
212
with respective error signal
204
and inverse error signal
216
. S
p
′ is HIGH when the magnitude of triangle waveform
212
exceeds error signal
204
, and S
p
′ is LOW when the magnitude of error signal
204
exceeds triangle waveform
212
. Likewise, S
n
′ is HIGH when the magnitude of triangle waveform
212
exceeds inverse error signal
216
, and S
n
′ is LOW when the magnitude of inverse error signal
214
exceeds triangle waveform
212
.
For example, the triangle waveform
212
is also biased to address cross-over distortion during the switching of switches
102
and
104
. Triangle waveform generator
220
generates triangle waveform
212
from a square wave input signal
222
. The direct current (DC) level of the triangle waveform
212
is adjusted by adding or subtracting bias signal
224
from triangle waveform
212
. The bias is normally adjusted such that, at input signal equal zero, both switches are on slightly more than 50% of the time, and an idle current exists in the inductors Ln and Lp, which keeps the diodes
108
and
110
clamped during the de-magnetization phase.
Referring to
FIG. 2B
, U.S. Pat. No. 6,373,336, entitled
Method of Attenuating Zero Crossing Distortion and Noise in an Amplifier, an Amplifier and Uses of the Method and the Amplifier
, inventors Niels Anderskouv and Lars Risbo, (referred to herein as the “Anderskouv-Risbo Patent”) describes an example of using dual pulse width modulators, PWM A and B, to drive respective half bridge amplifiers A and B connected to load
258
. A signal source
252
provides an input signal to inverting block
254
and noninverting block
256
. PWM A provides one output signal to drive the switches of Half bridge A, and PWM B provides one output signal to drive the switches of Half bridge B. The Anderskouv-Risbo Patent introduces a delay element &Dgr;T into the signal path between PWM B and half bridge B to prevent simultaneous switching of switches on the half bridges A and B and, thus, attenuate cross-over distortion. The Anderskouv-Risbo Patent does not teach providing appropriate signals to drive switches separately within a half bridge amplifier such as power converter circuit
100
. In contrast, the Stanley patent teaches switching techniques for use within a half bridge. Two copies of the Stanley circuit could be used for creating a full bridge circuit.
For example, the Stanley Patent, the Anderskouv-Risbo Patent, and others do not address the application of digital signal
Andersen Jack B.
Melanson John L.
Chambers Kent B.
Cirrus Logic Inc.
Hamilton & Terrile LLP
Jeanglaude Jean Bruner
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