U.S. patent number RE42,846 [Application Number 12/968,216] was granted by the patent office on 2011-10-18 for close-loop class-d audio amplifier and control method thereof.
This patent grant is currently assigned to Monolithic Power Systems, Inc.. Invention is credited to Yunping Lang, Yuancheng Ren, Junming Zhang.
United States Patent |
RE42,846 |
Zhang , et al. |
October 18, 2011 |
**Please see images for:
( Certificate of Correction ) ** |
Close-loop class-D audio amplifier and control method thereof
Abstract
The present invention discloses a Class-D power amplifier and
control method thereof. In one embodiment, the amplifier feeds back
the signal at the output node to the inverting input of the
comparator, and provides a high frequency triangular wave signal to
the non-inverting input of the comparator. In addition, the
non-inverting input of the comparator may be coupled to an offset
voltage, while the inverting input of the comparator may be coupled
to a fixed-frequency rectangular wave signal, a feedback signal
which is derived from the output stage and an input signal. In use,
the switching frequency may be at least substantially fixed, so as
to reduce the influence on the system caused by electromagnetic
interruption (EMI). Further, the control circuit is simple, and
some devices can be integrated.
Inventors: |
Zhang; Junming (Hangzhou,
CN), Ren; Yuancheng (Hangzhou, CN), Lang;
Yunping (Hangzhou, CN) |
Assignee: |
Monolithic Power Systems, Inc.
(San Jose, CA)
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Family
ID: |
40413471 |
Appl.
No.: |
12/968,216 |
Filed: |
December 14, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
12169539 |
Jul 8, 2008 |
7728666 |
Jun 1, 2010 |
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Foreign Application Priority Data
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Aug 16, 2007 [CN] |
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2007 1 0141041 |
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Current U.S.
Class: |
330/251; 330/291;
330/207A |
Current CPC
Class: |
H03F
3/217 (20130101) |
Current International
Class: |
H03F
3/217 (20060101) |
Field of
Search: |
;330/251,207A,291 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Patricia
Attorney, Agent or Firm: Zilka-Kotab, PC
Claims
What is claimed is:
1. A close-loop class-D power amplifier, comprising: an input stage
for receiving an input signals said input stage comprising a
comparator and one of a triangular wave generator and a rectangular
wave generator, said comparator receiving said input signal and one
of a high-frequency triangular wave generated by said triangular
wave generator and a high-frequency rectangular wave generated by
said rectangular wave generator, and outputting a first signal; an
output stage coupled to said input stage for responding to said
first signal and generating a second signal; a filter coupled to an
output node of said output stage for filtering said second signal
to get an output signal; and a feedback circuit coupled between an
output node of said output stage and an input node of said input
stage, said feedback circuit shaping said second signal to get a
feedback signal, and negatively feeding back said feedback signal
to said input stage, so as to subtract said feedback signal from
said input signal; wherein said high-frequency triangular wave is
applied to a non-inverting input of said comparator, while said
input signal and said feedback signal are applied to an inverting
input of said comparator, said comparator comparing said
high-frequency triangular wave with a signal which is gained by
subtracting said feedback signal from said input signal, to get
said first signal.
2. The class-D power amplifier as claimed in claim 1, wherein a DC
offset voltage is applied to a non-inverting input of said
comparator, while said input signal, said feedback signal and said
high-frequency rectangular wave are applied to an inverting input
of said comparator, said comparator comparing said DC offset
voltage with a signal which is gained by subtracting said feedback
signal from said input signal and adding said high-frequency
rectangular wave, to get said first signal.
3. The class-D power amplifier as claimed in claim 1, wherein said
feedback circuit comprises a capacitor, a first terminal of said
capacitor coupled to said input signal, an inverting input of an
amplifier and said second signal, a second terminal of said
capacitor coupled to ground or a DC offset voltage.
4. The class-D power amplifier as claimed in claim 3, wherein said
feedback circuit further comprises a feedback resistor coupled
between said first terminal of said capacitor and said second
signal.
5. The class-D power amplifier as claimed in claim 3, wherein said
capacitor is charged/discharged by one of said high-frequency
triangular wave and said high-frequency rectangular wave, and a
charge/discharge effect on said capacitor is stronger than that of
said second signal.
6. The class-D power amplifier as claimed in claim 1, wherein: said
output stage comprises: a drive circuit coupled to said comparator;
and a half-bridge switch circuit coupled to said drive circuit,
said half-bridge switch circuit being turned on alternately
according to drive signals generated by said drive circuit to
generate said second signal.
7. The class-D power amplifier as claimed in claim 1, wherein: said
output stage comprises: a drive circuit coupled to said comparator;
and two half-bridge switch circuits coupled to said drive circuit,
said two half-bridge switch circuits being turned on alternately
according to drive signals generated by said drive circuit to
generate two of said second signals and to feed back one of the two
said second signals.
8. The class-D power amplifier as claimed in claim 1, wherein: said
input stage comprises two of said comparator; and said output stage
comprises: a drive circuit coupled to the two of said comparator
separately; and two half-bridge switch circuits coupled to said
drive circuit separately, said two half-bridge switch circuits
being turned on alternately according to drive signals generated by
said drive circuit to generate two of said second signals, and to
feed back the two of said second signals to corresponding ones of
the two of said comparator.
9. A control method for a close-loop Class-D power amplifier,
comprising: receiving an input signal and one of a high-frequency
triangular wave generated by a triangular wave generator and a
high-frequency rectangular wave generated by a rectangular wave
generator; outputting a first signal; responding to said first
signal to generate a second signal; filtering said second signal to
generate an output signal; shaping said second signal to get a
feedback signal; and feeding back said feedback signal to an input
terminal which receives said input signal, so as to subtract said
feedback signal from said input signals wherein said high-frequency
triangular wave is applied to a non-inverting input of a
comparator, while said input signal and said feedback signal are
applied to an inverting input of said comparator, said comparator
comparing said high-frequency triangular wave with a signal which
is gained by subtracting said feedback signal from said input
signal, to get said first signal.
10. The method as claimed in claim 9, wherein a DC offset voltage
is applied to a non-inverting input of a comparator, while said
input signal, said feedback signal and said high-frequency
rectangular wave are applied to an inverting input of said
comparator, said comparator comparing said DC offset voltage with a
signal which is gained by subtracting said feedback signal from
said input signal and adding said high-frequency rectangular wave,
to get said first signal.
11. The method as claimed in claim 9, wherein a feedback circuit
comprises a capacitor, a first terminal of said capacitor coupled
to said input signal, an inverting input of an amplifier and said
second signal, a second terminal of said capacitor coupled to
ground or a DC offset voltage.
12. The method as claimed in claim 11, wherein said feedback
circuit further comprises a feedback resistor coupled between said
first terminal of said capacitor and said second signal.
13. The method as claimed in claim 11, wherein said capacitor is
charged/discharged by one of said high-frequency triangular wave
and said high-frequency rectangular wave, and a charge/discharge
effect on said capacitor is stronger than that of said second
signal.
14. The method as claimed in claim 9, wherein: an input stage
comprises a comparator; a drive circuit is coupled to said
comparator; and a half-bridge switch circuit is coupled to said
drive circuit, said half-bridge switch circuit being turned on
alternately according to drive signals generated by said drive
circuit to generate said second signal.
15. The method as claimed in claim 9, wherein: an input stage
comprises two comparators; a drive circuit is coupled to said
comparators; and two half-bridge switch circuits are coupled to
said drive circuit, said two half-bridge switch circuits being
turned on alternately according to drive signals generated by said
drive circuit to generate two of said second signal, and to feed
back one of the two said second signals.
16. The method as claimed in claim 9, wherein: an input stage
comprises two comparators; and an output stage comprises: a drive
circuit coupled to said two comparators separately; and two
half-bridge switch circuits coupled to said drive circuit
separately, said two half-bridge switch circuits being turned on
alternately according to drive signals generated by said drive
circuit to generate two of said second signal, and to feed back the
two of said second signal to corresponding ones of said two
comparators.
Description
RELATED APPLICATION DATA
This application claims the benefit of the filing date of .[.CN
application Serial.]. .Iadd.Chinese Patent Application .Iaddend.No.
.[.200710140141.2.]. .Iadd.200710141041.2 .Iaddend.filed on Aug.
16, 2007 and incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates generally to a Class-D power
amplifiers and particularly to a close-loop fixed-frequency Class-D
power amplifier and control method thereof.
DESCRIPTION OF RELATED ART
There are many different kinds of power amplifiers, such as
Class-A, Class-B, Class-AB, Class-D, etc. The Class-D power
amplifier is different from other amplifiers for it is a
switch-mode or pulse width modulation (PWM) power amplifier. In
such Class-D power amplifier, devices are either absolutely on, or
absolutely off, which highly reduces the power loss of the output
devices. An audio signal is used to modulate the PWM carrier signal
which drives the output power stage to get a high-frequency PWM
rectangular wave, and then the amplifier outputs the audio signal
to the load through a low-pass filter. At present, much attention
is paid to improve the power density and reduce the cost when the
Class-D power amplifier is designed. From the view of the circuit
structure the Class-D audio amplifier can be seen as a conventional
inverter which generates an amplified audio signal from a DC power
supply input according to a reference audio signal. Therefore, all
conventional close-loop feedback control methods can be used in
Class-D audio amplifiers such as instantaneous voltage mode
feedback control or voltage & current double feedback loops
control, etc. A typical device used in these control methods is an
error amplifier. So the circuit structures are not only complicated
but also high cost. The analog adaptive modulation (AAM) technology
which is owned by Monolithic Power Systems.RTM. (MPS.RTM.), Inc. is
a relatively simple method to realize the close-loop control of the
Class-D power amplifier.
As shown in FIG. 1, resistors R1 and R2 form a voltage divider in
the AAM structure. The voltage divider provides the non-inverting
input of the comparator Pin with an offset which equals to 1/2Vcc.
The comparator has an internal hysteresis loop. The comparator
compares the input signal at node B with 1/2Vcc.+-.dV, wherein dV
represents the hysteresis voltage of the comparator. The output PWM
wave of the comparator controls the transisitors M1 and M2 to be
turned on alternately through the drive circuit. The source of the
transistor M1 is coupled to the output node C, while the source of
the transistor M2 is grounded. The drain of the transistor M1 is
couple to the supply Vcc, while the drain of transistor M2 is
coupled to the output node C. The transistors M1 and M2 act as
switches, which constitute a part of the output stage of the
Class-D power amplifier circuit, so as to generate a rectangular
wave at the output node C when the output stage is used in switch
mode. The SW signal at the output node C is restored to an
amplified audio signal through a filter circuit composed of the
inductor L and capacitor C1, and the blocking capacitor C2, and
then delivered to the load (for example, a loudspeaker). Meanwhile,
the SW signal charges/discharges the capacitor Cint through the
resistor Rf to realize the adaptive control.
As shown in FIG. 2, when the output PWM rectangular wave at the
output node C is high, the capacitor Cint is charged and the
voltage at Nin (node B) increases until it reaches the upper limit
of the hysteresis loop. Then the high side transistor M1 is turned
off and the low side transistor M2 is turned on, which induces the
output PWM rectangular wave to be low. When the output PWM
rectangular wave at the output node C is low, the Cint is
discharged until the voltage at Nin decreases to lower limit of the
hysteresis loop. Then the low side transistor M2 is turned off and
the high side transistor M1 is turned on, which induces the output
PWM rectangular wave to be high. Such process is repeated to
generate the high-frequency PWM rectangular wave at node C which
will be filtered by the filter to get an amplified output audio
signal. The feedback circuit feeds back the signal at the node C to
the inverting input of the comparator to control the output audio
signal to follow the input audio signal, and realize a certain gain
amplification. The AAM technology allows a flexible gain set and
can achieve good audio performance both in single ended (SE) and
bridge tied load (BTL) structure. However, the switching frequency
varies heavily during the operation and some electromagenetic
interruption (EMI) problems may occur because the wide frequency
spectrum may drop into the audio band (FM/AM) and decrease the
sensitivity of FM/AM or disturb the video signal sometimes which
restricts the use of this technology on occasion of vehicle
electronics audio broadcast and so on.
Thus, it would be advantageous to provide a system and method that
overcome these and other drawbacks of the prior art. For example,
it would be advantageous to provide a fixed-frequency Class-D power
amplifier and method thereof for reducing the influence on the
system caused by EMI.
SUMMARY OF INVENTION
The present invention provides a method for close-loop control in a
Class-D power amplifier which can keep a fixed-frequency to avoid
the band of some important signals. The structure of the control
circuit is simple, and some devices can be integrated.
In accordance with an embodiment, a close-loop class-D power
amplifier is provided, comprising: an input stage for receiving an
input signal, said input stage comprises a comparator and a
triangular wave generator or a rectangular wave generator, said
comparator receives said input signal and the high-frequency
triangular wave generated by said triangular wave generator or the
high-frequency rectangular wave generated by said rectangular wave
generator, and then outputs a first signal; an output stage coupled
to said input stage, responds to said first signal to generate a
second signal; a filter coupled to the output node of said output
stages for filtering said second signal to get an output signal;
and a feedback circuit, coupled between the output node of said
output stage and the input node of said input stage, shapes said
second signal to get a feedback signal which is negatively feedback
to said input stage, so as to subtract said feedback signal from
said input signal.
In accordance with the power amplifier described above, said
high-frequency triangular wave may be applied to the non-inverting
input of said comparator, while said input signal and said feedback
signal may be applied to the inverting input of said comparator,
where said comparator may compare said high-frequency triangular
wave with a signal which is gained by subtracting said feedback
signal from said input signal, so as to get said first signal.
In accordance with the power amplifier described above, the DOC
offset voltage may be applied to the non-inverting input of said
comparator, said input signal, said feedback signal and said
high-frequency rectangular wave may be applied to the inverting
input of said comparator, where said comparator may compare said DC
offset voltage with a signal which is gained by subtracting said
feedback signal from said input signal and then adding it to said
high-frequency rectangular wave, so as to get said first
signal.
In accordance with the power amplifier described above, said
feedback circuit may comprise a capacitor, the first terminal of
said capacitor optionally coupled to said input signal, the
inverting input of said comparator and said second signal, while
the second terminal of said capacitor may be coupled to ground or
the DC offset voltage.
In accordance with the power amplifier described above, said
feedback circuit may further comprise a feedback resistor coupled
between the first terminal of said capacitor and said second
signal.
In accordance with the power amplifier described above, the
chage/discharge effect on said capacitor of said high-frequency
triangular wave or said high-frequency rectangular wave may be
stronger than that of said second signal.
In accordance with the power amplifier described above, said input
stage may comprise said comparator; and said output stage may
comprise: a drive circuit coupled to said comparator; a half-bridge
switch circuit coupled to said drive circuit, which may be
alternately turned on according to the drive signals generated by
said drive circuit, to generate one said second signal
accordingly.
In accordance with the power amplifier described above, said input
stage may comprise said comparator; and said output stage may
comprise: a drive circuit coupled to said comparator; two
half-bridge switch circuits coupled to said drive circuit, which
may be alternately turned on according to the drive signals
generated by said drive circuit, to generate two said second
signals accordingly, and feed back one thereinto.
In accordance with the power amplifier described above, said input
stage may comprise two said comparators; and said output stage may
comprise: a drive circuit, coupled to said comparators separately;
two half-bridge switch circuits coupled to said drive circuit
separately, which may be alternately turned on according to the
drive signals generated by said drive circuit, to generate two said
second signals accordingly, and feed back signals to corresponding
comparator separately.
In accordance with another embodiment, a control method for a
close-loop class-D power amplifier is provided, comprising
receiving an input signal and a high-frequency triangular wave
generated by a triangular wave generator or a high-frequency
rectangular wave generated by a rectangular wave generator, and
outputting a first signal; responding to said first signal to
generate a second signal; filtering said second signal to get an
output signal; and shaping said second signal to get a feedback
signal, and feeding back said feedback signal to the input terminal
which receives said input signal, so as to subtract said feedback
signal from said input signal.
In accordance with the control method described above, said first
signal is responded in order to generate two of said second
signals, at least one of the two said second signals are shaped,
and the shaped signals are fed back to said input terminal.
The class-D power amplifier may use a comparator with a hysteresis
loop which is small enough to be neglected instead of the
hysteresis comparator used in the AAM structure. The low frequency
pad of the signal output from the power stage may be counteracted
with the input audio signal at the input terminal of the
comparator, while the high frequency part may be sent to the
comparator, so as to get a modulated output audio signal at the
output terminal.
The non-inverting input of the comparator may be coupled to a
fixed-frequency triangular wave signal, while the inverting input
of the comparator may be coupled to the feedback signal from the
output stage and an input signal.
As another options the non-inverting input of the comparator may be
coupled to a DC offset voltage Vdd, while the inverting input of
the comparator may receive a fixed-frequency rectangular wave
signal, the feedback signal from the output stage and an input
signals.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be further understood with reference to
the following detailed description and the appended drawings,
wherein like elements are provided with like reference signs.
FIG. 1 illustrates a drive circuit of the prior art AAM Class-D
power amplifier;
FIG. 2 is the operation waveform of the prior art AAM Class-D power
amplifier;
FIG. 3 illustrates a schematic circuit used in a SE Class-D power
amplifier, in accordance with one embodiment;
FIG. 4 illustrates the waveforms of the input audio signal and the
output audio signal of the circuit shown in FIG. 3, in accordance
with another embodiment;
FIG. 5 illustrates the waveforms of the SW signal, the signal at
the non-inverting input Pin and the signal at the inverting input
Nin of the circuit shown in FIG. 3, in accordance with another
embodiment;
FIG. 6 illustrates a schematic circuit used in a SE Class-D power
amplifier, in accordance with still another embodiment;
FIG. 7 illustrates the waveforms of the input audio signal and the
output audio signal of the circuit shown in FIG. 6, in accordance
with another embodiment;
FIG. 8 illustrates the waveforms of the rectangular wave, the SW
signal, the signal at the non-inverting input Pin and the signal at
the inverting input Nin of the circuit shown in FIG. 6, in
accordance with another embodiment;
FIG. 9 illustrates a schematic circuit used in a BTL Class-D power
amplifier, in accordance with still another embodiment;
FIG. 10 (a) and FIG. 10 (b) illustrate part of the waveforms of the
circuit shown in FIG. 9, in accordance with another embodiment;
FIG. 11 illustrates a schematic circuit used in a BTL Class-D power
amplifier, in accordance with another embodiment;
FIG. 12 (a) and FIG. 12 (b) illustrate part of the waveforms of the
circuit shown in FIG. 11, in accordance with another
embodiment.
FIG. 13 is the flow chart of a control method for a close-loop
Class-D power amplifier, in accordance with another embodiment.
DETAILED DESCRIPTION
FIG. 3 illustrates a schematic circuit in accordance with one
embodiment, comprising a Class-D amplifier circuit and a load. A
proper high-frequency (about hundreds of KHz) triangular wave with
1/2Vcc offset is applied to the non-inverting input of the
comparator Pin (A) whose inverting input is Nin (B) coupled to
ground through the capacitor Cint. The input audio signal
charges/discharges the capacitor Cint through the resistors Ri and
the capacitor Cin. The output PWM wave of the comparator controls
the transistors M1 and M2 to be turned on alternatively through the
drive circuit, wherein the source of the transistor M1 is connected
to the output node C while the source of the transistor M2 is
grounded. The drain of the transistor M1 is connected to power
supply Vcc, while the drain of the transistor M2 is connected to
the output node C. The transistors M1 and M2 act as switches that
form a part of the output stage of the Class-D amplifier circuit to
generate a rectangular wave output at the output node C when the
output stage is used in switch mode. SW signal at the output node C
is restored to an amplified audio signal through a filter circuit
comprising the inductor L and capacitor C1, and the blocking
capacitor C2, and then delivered to the load (for example, a
loudspeaker). Meanwhile, the SW signal charges/discharges the
capacitor Cint through the resistor Rf. The charge/discharge
effects produced by the audio signal and the SW signal at the
output node C may be exactly counteracted. Thus, the inverting
input of the comparator Nin may keep following the voltage of the
non-inverting input of the comparator Pin under the function of
both Vsw_low and the audio input signal. When the output of the
comparator is high, the transistor M1 is turned on and the
transistor M2 is turned off. The voltage V.sub.Nin at the inverting
input of the comparator Nin is compared with a sum of the voltage
at the non-inverting input of the comparator Pin and the hysteretic
voltage dV, Vpin+dV (wherein dV represents hystereric voltage of
the comparator). The SW signal is high at this time, which after
feedback causes the voltage at Nin to raise till it becomes larger
than the voltage Vpin+dV. Then the output of the comparator becomes
low, the transistor M1 is turned off and the transistor M2 is
turned on. The voltage at the inverting input of the comparator Nin
is compared with the voltage Vpin-dV at this time. The feedback of
the low SW signal causes the voltage at Nin to drop till it becomes
less than the voltage Vpin-dV. The output of the comparator becomes
high, causing the SW signal to be high, circularly (e.g. as shown
in FIG. 5). Therefore, to realize fixed-frequency feedback control
and ensure the system working steadily, the raising and dropping
rates of the voltage at Nin may optionally be less than the
changing slope of the given triangular wave at Pin. So the changing
slope of the triangular wave may be taken into consideration when
the capacitor Cint and the feedback resistor Rf are designed. The
gate drive signals of the transistors M1 and M2 can be gained from
the high-frequency part of the SW signal under the modulation of
the high-frequency triangular carrier wave of non-inverting input
Pin. The gain of the amplifier is confirmed by the ratio of
resistors Rf and Ri.
Optional embodiments of key operation waveforms of the circuit in
FIG. 3 are illustrated in FIG. 4 and FIG. 5. Switch control method
in accordance with another embodiment is apparent in FIG. 5. When
the input audio signal changes, the SW signal can be adaptively
modulated by this system to let the voltage at the inverting input
Nin always follow the non-inverting input Pin so as to control the
output. Of course, the switching frequency is not unchangeable but
has a minor change at the range of hundreds of HZ. This change is
caused by the small audio sine signal at the inverting input of the
comparator which also can charge/discharge the capacitor Cint.
However, the change like this is very small relative to the
switching frequency, so this control method can be seemed as a
fixed-frequency control all the same.
FIG. 6 illustrates a schematic circuit in accordance with another
embodiment. Its basic configuration is similar to FIG. 1 except
that the triangular wave applied to the non-inverting input Pin in
FIG. 1 is replaced by a rectangular wave with 1/2 Vcc offset
applied to the inverting input Nin via the resistor Rs while the
non-inverting input of the comparator Pin is directly coupled to
1/2 Vcc DC offset. The charge/discharge effect on the capacitor
Cint of the rectangular wave is similar to the effect of the
triangular wave directly applied to the non-inverting input Pin of
the comparator. In former embodiments the slope rate of the given
triangular wave may need to be always larger than that of the
voltage at the inverting input Nin, i.e. the high-frequency
charge/discharge ripple at the integral capacitor Cint. The
charge/discharge effect on the capacitor Cint of the triangular
wave may also need to be stronger than the charge/discharge effect
of the feedback signal SW. Likewise, in this embodiment, the
charge/discharge effect on the capacitor Cint of the given
rectangular wave may need to be stronger than the effect of the
feedback signal SW.
Optional embodiments of key operation waveforms of the circuit in
FIG. 6 are illustrated in FIG. 7 and FIG. 8. Referring to FIG. 8, a
period cycle can be divided into 5 phases:
Phase 1 (t0-t1): At t=t0, the rectangular wave becomes low. The SW
signal and the rectangular wave signal discharge the capacitor Cint
at the same time. The voltage Vcint of the capacitor Cint keeps
falling.
Phase 2 (t1-t2): At t=t1, Vcint<1/2Vcc, the output of the
comparator is reversed, and the SW signal becomes high. The SW
signal charges Cint while the rectangular wave keeps discharging
Cint at the same time. Since the discharge effect is stronger,
Vcint keeps failing at a slow rate.
Phase 3 (t2-t3): At t=t2, the rectangular wave becomes high. The SW
signal and the rectangular wave charge the Cint at the same time.
Vcint raises.
Phase 4 (t3-t4): At t=t5, Vcint>1/2Vcc, the output of the
comparator is reversed again, and the SW signal becomes low. The SW
signal discharges Cint while the rectangular wave keeps charging
Cint at the same time. Since the charge effect is stronger, Vcint
keeps raising at a slow rate.
Phase 5 (t4-t5): At t=t4, the rectangular wave becomes low. The SW
signal and the rectangular wave discharge the Cint at the same
time. Vcint falls.
As mentioned before, to realize the proposed fixed-frequency
feedback control of this embodiment, the voltage at Nin may be
required to keep falling when the SW signal becomes high in Phase 2
and keep raising in Phase 4. The following formula may need to be
fulfilled while the feedback resistor Rf, the voltage Vrectangular
of the rectangular wave with 1/2 Vcc offset, the SW signal Vsw and
the resistor Rs are designed:
> ##EQU00001##
Accordingly, the charge/discharge effect on the capacitor Cint of
the given rectangular wave may be required to be stronger than the
effect of the feedback signal SW in this embodiment. Since the
charge/discharge effect on the capacitor of the rectangular wave is
greatly stronger than the effect of feedback signal SW, although
there is a change with hundreds of HZ, the frequency of the SW
signal which is decided by the frequency of the rectangular wave is
fixed as a whole.
Similar to the SE Class-D power amplifier mentioned before, the
present invention also can be used in BIT power amplifier. Harmonic
distortion and DC offset can be eliminated by the inherence
differential output structure of the bridge type topology. FIG. 9
illustrates a schematic circuit in accordance with another
embodiment. The H-bridge comprises 2 half-bridge switching circuits
which are powered by single power supply Vcc generally. For given
Vcc, the max amplitude of the output signal in H-bridge circuit is
2 timers larger than which in single ended manner, while the output
power is 4 timers larger. Only one comparator is used, whose output
controls the transistors S1,S2,SS3 and S4 to be turned on
alternately through the drive circuit so as to get two phase
opposite signals SW1 and SW2 which are delivered to the load
through the filter L1, C1 and L2, C2, Only one of the SW1 and SW2
may need to be fed back and used in feedback control loop. In FIG.
9 SW2 is used as a feedback signal FIG. 11(a) illustrates optional
waveforms of audio input and audio output of the circuit shown in
FIG. 9, while FIG. 10(b) illustrates optional partly magnified
operation waveforms in which the SW1 signal can be gained through
the phase-reversal of the SW2 signal.
FIG. 11 illustrates a schematic circuit in accordance with another
embodiment in BTL amplifier systems. In this embodiment, each
half-bridge has its own special comparator to control two drive
circuits separately. The switching frequency of each bridge is the
same since they are set by the same external triangular wave at the
Node A. The structure of the control circuit of each bridge is
similar to that in the SE amplifier except the absence of the
blocking capacitor (referring to the capacitor C2 in FIG. 3 and
FIG. 6), and the gain may also be calculated by Rf/Ri. The input
audio signal is a differential signal which is phase opposites
applied at the inverting inputs B1 and B2 of the two comparators
and compared with the triangular wave. FIG. 12 (a) illustrates an
embodiment of the waveforms of the audio input and audio output of
the circuit shown in FIG. 11, while FIG. 12(b) illustrates an
embodiment of the partly magnified operation waveforms.
The drive circuits in FIG. 3, FIG. 6, FIG. 9 and FIG. 11 can be
implemented by gate drive circuit or other circuits which can
achieve the same function as an option. In addition, the number of
the drive circuits in FIG. 3, FIG. 6, FIG. 9 and FIG. 11 is only
schematically shown by way of example, and thus only needs to
fulfill that the drive circuits can be controlled by respective
comparator and drive respective transistor, rather than be the same
with the number of the blocks representative of the drive circuits
in the Figures mentioned above.
Referring to FIG. 13, a control method for a close-loop Class-D
power amplifier in accordance with one embodiment comprises the
following operations:
Receive an input signal and a high-frequency triangular wave
generated by a triangular wave generator or a high-frequency
rectangular wave generated by a rectangular wave generator, and
output a first signal;
Respond to said first signal and generate a second signal, e.g. the
SW signal;
Filter the SW signal to get an output signal; and
Shape the SW signal to get a feedback signal, and feed back said
feedback signal to the input terminal which also receives said
input signal, so as to subtract the feedback signal from said input
signal. Compared to the prior art AAM scheme, the present
embodiment may only need to add a DC power supply with a 1/2 Vcc
offset and a proper triangular wave or rectangular wave. After the
integration of these parts, the close-loop fixed-frequency control
of the Class-D power amplifier can be simply achieved.
The above detailed description of embodiments of the present
invention is not intended to be exhaustive or to limit the
invention to the precise form disclosed above. While specific
embodiments of, and examples for, the invention are described above
for illustrative purposes, various equivalent modifications are
possible within the scope of the invention, as those skilled in the
relevant art will recognize.
The terminology used in the Detailed Description is intended to be
interpreted in its broadest reasonable manner, even though it is
being used in conjunction with a detailed description of certain
specific embodiments of the invention. Certain terms may even be
emphasized; however, any terminology intended to be interpreted in
any restricted manner will be overtly and specifically defined as
such in this Detailed Description section. In general, the terms
used in the following claims should not be construed to limit the
invention to the specific embodiments disclosed in the
specification, unless the above Detailed Description section
explicitly defines such terms. Accordingly, the actual scope of the
invention encompasses not only the disclosed embodiments, but also
all equivalent ways of practicing or implementing the invention
under the claims.
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