U.S. patent application number 10/639503 was filed with the patent office on 2004-09-23 for output control apparatus of pulse width modulator.
This patent application is currently assigned to Sonix Technology Co.. Invention is credited to Chang, Jung-Lin, Ho, Sheng-Yi, Wei, Wei-Hsin.
Application Number | 20040183579 10/639503 |
Document ID | / |
Family ID | 32986162 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040183579 |
Kind Code |
A1 |
Wei, Wei-Hsin ; et
al. |
September 23, 2004 |
OUTPUT CONTROL APPARATUS OF PULSE WIDTH MODULATOR
Abstract
The invention provides an output control apparatus for adjusting
the output level of a pulse width modulation (PWM) signal by
changing the amplitude level of the output PWM signal. The output
control apparatus comprises a control signal generator, a
digital-to-analog converter (DAC), and an output circuit. The
control signal generator generates a digital control signal. The
DAC outputs a predetermined level according to the digital control
signal. The output circuit with a negative feedback loop receives
the PWM signal and receives the predetermined level by the negative
feedback loop. While the PWM signal is logic number "0", the
negative feedback loop is not switched on, so as to control the
level of the PWM signal at a base level. While the PWM signal is
logic number "1", the negative feedback loop is switched on, so as
to control the level of the PWM signal at the predetermined
level.
Inventors: |
Wei, Wei-Hsin; (Chupei City,
TW) ; Ho, Sheng-Yi; (Chupei City, TW) ; Chang,
Jung-Lin; (Chupei City, TW) |
Correspondence
Address: |
TROXELL LAW OFFICE PLLC
SUITE 1404
5205 LEESBURG PIKE
FALL CHURCH
VA
22041
US
|
Assignee: |
Sonix Technology Co.
|
Family ID: |
32986162 |
Appl. No.: |
10/639503 |
Filed: |
August 13, 2003 |
Current U.S.
Class: |
327/172 |
Current CPC
Class: |
H03F 3/217 20130101;
H03G 3/3021 20130101; H03G 3/00 20130101 |
Class at
Publication: |
327/172 |
International
Class: |
H03K 003/017 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2003 |
TW |
092106074 |
Claims
What is claimed is:
1. A control apparatus for controlling a level of a pulse width
modulation signal (PWM signal) generated by a pulse width modulator
(PWM), the apparatus comprising: a control signal generator for
generating a digital control signal; a digital-to-analog converter
(DAC) for outputting a predetermined level according to the digital
control signal; and an output circuit with a negative feedback loop
for receiving the PWM signal, and receiving the predetermined level
by the negative feedback loop; while the PWM signal is logic number
"0", not switching on the negative feedback loop, so as to control
the level of the PWM signal at a base level; and while the PWM
signal is logic number "1", switching on the negative feedback
loop, so as to control the level of the PWM signal at the
predetermined level.
2. The apparatus of claim 1, wherein the control signal generator
is an N bits structure for generating 2.sup.N kinds of different
digital control signals.
3. The apparatus of claim 2, wherein the DAC generates 2.sup.N
kinds of different predetermined levels according to the 2.sup.N
kinds of different digital control signals.
4. The apparatus of claim 1, wherein the DAC further comprises: a
decoder for converting the digital control signal to a
corresponding level control signal; a plurality of analog switches,
each analog switches switching on or off being controlled by the
level control signal; and a plurality of resistances connecting to
a power supply for determining the predetermined level according to
the allocation of the plurality of analog switches.
5. The apparatus of claim 1, wherein the output circuit further
comprises a receiving element for receiving the PWM signal and
judging the PWM signal is logic number "0" or "1".
6. The apparatus of claim 1, wherein the output circuit further
comprises a base level input for providing the base level.
7. The apparatus of claim 6, wherein the output circuit further
comprises a plurality of switch components for while the PWM signal
is logic number "0", not switching on the negative feedback loop
but switching on the base level input to control the level of the
PWM signal at the base level; and while the PWM signal is logic
number "1", switching on the negative feedback loop to control the
level of the PWM signal at the predetermined level.
8. The apparatus of claim 7, wherein the negative feedback loop
further comprises an amplifier combination for receiving the
predetermined level, and while the negative feedback loop is
switched on, setting the level of the PWM signal equal to the
predetermined level.
9. An output control apparatus for controlling an output level of a
PWM signal at a predetermined level, the output control apparatus
comprising: an input for inputting the PWM signal; a predetermined
level input for providing a predetermined level; a base level input
for providing a base level; a high level input for providing a
highest level; a level output for outputting an output level of the
PWM signal; a switch combination comprising a plurality of switches
for connecting to the input, the base level input, and the high
level input; and an amplifier comprising: an inverting input for
inputting the predetermined level; a non-inverting input for
connecting to the level output; and an amplifier output for
connecting to the switch combination; wherein, while the PWM signal
is logic number "0", the switch combination switches on the base
level input and connects the amplifier output to the high level
input to make the amplifier not be switched on, so as to control
the level of the PWM signal at the base level; and wherein, while
the PWM signal is logic number "1", the switch combination doesn't
switch on the base level input and connects the amplifier output to
the level output to make the amplifier and the switch combination
form a negative feedback loop, so as to control the level of the
PWM signal at the predetermined level.
10. The output control apparatus of claim 9, further comprising a
control signal generator for generating a digital control
signal.
11. The output control apparatus of claim 10, further comprising a
DAC for receiving the digital control signal and outputting the
predetermined level to the predetermined level input, wherein the
predetermined level is determined by the digital control
signal.
12. The apparatus of claim 11, wherein the control signal generator
is a N bits structure for generating 2.sup.N kinds of different
digital control signals.
13. The apparatus of claim 11, wherein the DAC further comprises: a
decoder for converting the digital control signal to a
corresponding level control signal; a plurality of analog switches,
each analog switches switching on or off being controlled by the
level control signal; and a plurality of resistances connecting to
a power supply for determining the predetermined level according to
the allocation of the plurality of analog switches.
14. The apparatus of claim 12, wherein the DAC generates 2.sup.N
kinds of different predetermined levels according to the 2.sup.N
kinds of different digital control signals.
15. An output control apparatus for controlling an output level of
a PWM signal at a predetermined level, the output control apparatus
comprising: a set of differential inputs for differentially
inputting the PWM signal; a predetermined level input for providing
a predetermined level; a set of base level inputs for providing a
base level; a set of high level inputs for providing a highest
level; a set of differential level outputs for differentially
outputting an output level of the PWM signal; a switch combination
comprising a plurality of switches for connecting to the set of
differential inputs, the set of base level inputs, and the set of
high level inputs; and an amplifier combination comprising a
plurality of amplifiers, each amplifier connecting to a
differential input of the set of differential inputs, a base level
input of the set of base level inputs, a high level input of the
set of high level inputs, and a differential level input of the set
of differential level inputs, each the amplifier comprising: an
inverting input for inputting the predetermined level; a
non-inverting input for connecting to the differential level
output; and an amplifier output for connecting to the switch
combination; wherein while the PWM signal is logic number "0", the
switch combination switches on the base level input and connects
the amplifier output to the high level input to make the amplifier
not be switched on, so as to control the level of the PWM signal at
the base level; and while the PWM signal is logic number "1", the
switch combination doesn't switch on the base level input and
connects the amplifier output to the level output to make the
amplifier combination and the switch combination form a negative
feedback loop, so as to control the level of the PWM signal at the
predetermined level.
16. The output control apparatus of claim 15, further comprising a
control signal generator for generating a digital control
signal.
17. The output control apparatus of claim 16, further comprising a
DAC for receiving the digital control signal and outputting the
predetermined level to the predetermined level input; wherein the
predetermined level is determined by the digital control
signal.
18. The apparatus of claim 17, wherein the control signal generator
is an N bits structure for generating 2.sup.N kinds of different
digital control signals.
19. The apparatus of claim 17, wherein the DAC further comprises: a
decoder for converting the digital control signal to a
corresponding level control signal; a plurality of analog switches,
each analog switches switching on or off being controlled by the
level control signal; and a plurality of resistances connecting to
a power supply for determining the predetermined level according to
the allocation of the plurality of analog switches.
20. The apparatus of claim 18, wherein the DAC generates 2.sup.N
kinds of different predetermined levels according to the 2.sup.N
kinds of different digital control signals.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is an output control apparatus of a
pulse width modulator; it is especially an output control apparatus
that can adjust the output amplitude of a pulse width modulation
signal (PWM signal).
[0003] 2. Description of the Prior Art
[0004] The method of audio output of the pulse width modulation
(PWM) has been applied to consumer products extensively, especially
in portable electronic products. For portable electronic products
that use batteries as the power source, the power consumption is
one of the most concerned considerations. The biggest advantage of
the output method of the PWM is its high power and efficiency.
[0005] Please refer to FIG. 1. FIG. 1 is a schematic diagram of an
audio output apparatus 10 of the PWM according to the prior art.
The audio output apparatus 10 of the PWM according to the prior art
comprises a digital volume controller 12, a pulse code modulation
to pulse width modulation converter (PCM-to-PWM converter) 14, a
PWM output circuit 20, and an speaker 16. To complete an audio
output with the PWM technology of the prior art, if adjustment of
volume is necessary, it would be done as shown in FIG. 1. The audio
data of the audio source is processed by pulse code modulation
first; then, the PCM data is transferred to the digital volume
controller 12. The user then inputs a volume control signal to make
the digital volume controller 12 adjusts the value of the PCM
data.
[0006] As shown in FIG. 1, the PCM data processed by the digital
volume controller 12 is transferred to the PCM-to-PWM converter 14
for converting the PCM data to the PWM signal. Then, via the PWM
output circuit 20 triggering the speaker 16, the signal is being
sent out as audio sound. Because the PWM output circuit 20
according to the prior art can only output at a fixed level, the
value of the PCM data needs to be adjusted to change the duty of
the PWM signal output.
[0007] Please refer to FIG. 2. FIG. 2 is a schematic diagram of the
output circuit 20 and the speaker 16 shown in FIG. 1. The output
circuit 20 of the PWM according to the prior art comprises two
inverters 22, 24, and four power transistors M0, M1, M2, M3.
[0008] As shown in FIG. 2, PI and NI represent the input signals
that are differential PWM signal. Through the combination circuit
that comprises the power transistors M0.about.M3, the output level
of the input signal is being controlled at a fixed value. PO and NO
represent the output, and the output circuit 20 drives the speaker
16 according to the input signal and the fixed level. The power
transistors M0.about.M3 can be taken as the switches of the
circuit. While the input signal is logic number "0", the power
transistors M0 /or M2 are not switched on, but the power
transistors M1 /or M3 are switched on. Therefore, the output signal
level of the output PO /or NO is close to the low level VSS. While
the input signal is logic number "1", the power transistors M1 /or
M3 are not switched on, but the power transistors M0 /or M2 are
switched on; the output signal level of the outputs PO /or NO is
then close to the high level VDD.
[0009] The inverters 22, 24 are used for changing the polarity of
the input signals PI and NI to make PI/NI and PO/NO in the same
phase. PO and NO are the pulse signals with 0.about.100% duty, and
the converting frequency of the pulse signals may be 10.about.100
kilohertz. For the coil within the speaker 16, the equivalent
impedance in the converting frequency is very high while the
current in the frequency within the coil is very low, so the power
consumption is also lower.
[0010] Please refer to FIG. 3. FIG. 3 is a schematic diagram of the
signal of adjusting the output volume of the output apparatus 10
shown in FIG. 1. Two sets of signal group 32, 34 are shown in FIG.
3. The PWM output signal of the prior art is shown as group 32, and
the PWM output signal of the prior art which the volume is reduced
by 1/2 is shown as group 34. In FIG. 3, the signals output by PO
and NO are described by the differential way, wherein Ts is the
signal cycle time, and Td is the duty of each pulse of the output
signals. As shown in FIG. 3, in the prior art, the input volume is
reduced by reducing the duty of the original PWM output signal,
without changing the output level of the signal.
[0011] However, the noise of the mixed signal of the PWM output
signal becomes bigger with the output level yet doesn't become
smaller with the duty. Therefore, the method of reducing volume of
the prior art will show the noise of the background, making the
audio quality become worse. In view of this, the present invention
proposes a new framework to adjust the volume by adjusting the
output pulse level to avoid the problem of worse audio quality at
lower volume and to achieve the objective of improving the audio
quality.
SUMMARY OF THE INVENTION
[0012] An objective of the present invention is to provide an
output control apparatus of a pulse width modulator for adjusting
the output level of the PWM output signal, thus to avoid the
problem of the audio quality getting worse with lower volume, and
to achieve the objective of improving the audio quality.
[0013] The present invention provides an output control apparatus
for controlling the output level of a PWM signal at a predetermined
level. The output control apparatus comprises an input, a
predetermined level input, a base level input, a high level input,
a level output, a switch combination, and an amplifier. The input
is used for inputting the PWM signal. The predetermined level input
is used for providing a predetermined level. The base level input
is used for providing a base level. The high level input is used
for providing the highest level. The level output is used for
outputting an output level of the PWM signal. The switch
combination comprises a plurality of switches for connecting to the
input, the base level input, and the high level input. The
amplifier combination comprises an inverting input for inputting
the predetermined level, a non-inverting input for connecting to
the output, and an amplifier output for connecting to the switch
combination.
[0014] While the PWM signal received by the output control
apparatus according to the present invention is logic number "0",
the switch combination switches on the base level input and
connects the amplifier output of each amplifier within the
amplifier combination to the high level input, making the amplifier
combination not being switched on, so as to control the level of
the PWM signal at the base level.
[0015] While the PWM signal received by the output control
apparatus is logic number "1", the switch combination doesn't
switch on the base level input and connects the amplifier output of
each the amplifier to the level output to make the amplifier
combination and the switch combination form a negative feedback
loop, so as to control the level of the PWM signal at the
predetermined level.
[0016] A control signal generator and a DAC generate the
predetermined level input by the predetermined level input of the
present invention. The control signal generator, according to the
user control, generates various digital control signals and
transfers the signals to the DAC. The DAC converts the digital
control signals to a corresponding predetermined level and inputs
the predetermined level to the output control apparatus via the
predetermined level input.
[0017] Therefore, the present invention achieves the objective of
adjusting the output amplitude of the PWM signal by controlling the
predetermined level and improves the problem that the prior art
has, which is to reduce the output volume only by improving the
duty of the PWM signal but enlarging the mixed signals.
[0018] The advantage and spirit of the present invention may be
understood by the following recitations together with the appended
drawings.
BRIEF DESCRIPTION OF THE APPENDED DRAWINGS
[0019] FIG. 1 is a schematic diagram of an audio output apparatus
of the PWM according to the prior art.
[0020] FIG. 2 is a schematic diagram of the output circuit and the
speaker shown in FIG. 1.
[0021] FIG. 3 is a schematic diagram of the signal of adjusting the
output volume of the output apparatus shown in FIG. 1.
[0022] FIG. 4 is a schematic diagram of an output control apparatus
and its application according to the present invention.
[0023] FIG. 5 is a function block diagram of the output control
apparatus shown in FIG. 4.
[0024] FIG. 6 is a schematic diagram of an output circuit of an
embodiment according to the present invention.
[0025] FIG. 7 is a schematic diagram of an output circuit of
another embodiment according to the present invention.
[0026] FIG. 8 is a schematic diagram of the control signal
generator and the DAC of 4 bits structure according to the present
invention.
[0027] FIG. 9 is a schematic diagram of the output level of the PWM
signal in comparing the prior art and the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Please refer to FIG. 4. FIG. 4 is a schematic diagram of an
output control apparatus 40 and its application according to the
present invention. The output control apparatus 40 of the present
invention in FIG. 4 is used for controlling the output volume.
Before outputting the audio signal, the pulse code modulation data
(PCM data) that represents the audio signal should be processed by
the PCM-to-PWM converter 14 first to convert the PCM data to the
PWM signal. After that, the output control apparatus 40 receives
the PWM signal and external volume control. Then, via the output
control apparatus 40, the output level of the PWM signal changes
according to the volume control. Because the output level to push
the speaker 16 changes according to the volume control, the volume
output by the speaker 16 is controlled. One thing should be noticed
here, the output control apparatus 40 of the present invention
doesn't achieve the objective of changing the volume by changing
the duty of the PWM signal. Therefore, the present invention
doesn't suffer the problem of the prior art.
[0029] Please refer to FIG. 5. FIG. 5 is a function block diagram
of the output control apparatus 40 shown in FIG. 4. The output
control apparatus 40 of the present invention is used for
controlling the level of a PWM signal generated by a pulse width
modulator, wherein the output control apparatus 40 comprises a
control signal generator 42, a DAC 44, and an output circuit 50.
The output control apparatus 40 makes the output circuit 50 receive
a PWM signal and the control signal generator 42 receive the volume
control corresponding to the PWM signal at the same time.
[0030] Please refer to FIG. 6. FIG. 6 is a schematic diagram of an
output circuit 50 of an embodiment according to the present
invention. The output circuit 50 comprises an input VI, a
predetermined level input DAO, a base level input VSS, a high level
input VDD, a level output VO, a switch combination 52, and an
amplifier 54. The input VI is used for inputting the PWM signal.
The predetermined level input DAO is used for providing a
predetermined level. The base level input VSS is used for providing
a base level. The high level input VDD is used for providing the
highest level. The level output VO is used for outputting an output
level of the PWM signal.
[0031] The switch combination 52 comprises a plurality of switches.
The embodiment in FIG. 6 takes the power transistor as the switch
and forms the switch combination 52 with three switches S1, S2, S3.
As shown in FIG. 6, the switch S1 is used for connecting to the
output VO, the base level input VSS, and the input VI; the switch
S2 is used for connecting to the amplifier output, the high level
input VDD, and the output VO; the switch S3 is used for connecting
to the high level input VDD, the input VI, and the amplifier
output. The present invention controls the circuits between each
element being opened or closed by cooperating with the three
switches S1, S2 and S3. Wherein, the speaker 16 in FIG. 6 further
connects to a ground, in practical application, the speaker may
connect to the high level input VDD or the base level input
VSS.
[0032] The amplifier 54 comprises an inverting input (-), a
non-inverting input (+), and an amplifier output. The inverting
input (-) is used for connecting to the predetermined level input
DAO to input the predetermined level. The non-inverting input (+)
is used for connecting to the output VO. The amplifier output is
used for connecting to the switch S1 and S3.
[0033] The key of the present invention lies in how to control and
adjust the output level of the PWM signal. As shown in FIG. 6,
while the PWM signal being input into the input VI is logic number
"0", the transistor switches S3 and S2 cooperate to connect the
amplifier output with the high level input VDD, so that the
amplifier is not switched on. The transistor switch S1 connects the
output VO with the base level input VSS to make the output can be a
base level, and at this condition, the result is the same as the
output circuit of the pulse width modulation apparatus of the prior
art.
[0034] While the PWM signal being input into the input VI is logic
number "1", the transistor switch S1 is not switched on, and the
output VO is connected to the amplifier output by the transistor
switch S2. At this time, the amplifier 54 and the transistor switch
S1 form a negative feedback loop 46 (shown in FIG. 5) to make the
signal output level of the output VO be about the same as to the
predetermined level of the predetermined level input DAO.
Therefore, the output level of the output VO at logic number "1"
may be adjusted by changing the voltage of the predetermined level
input DAO.
[0035] Because of the PWM signal of the prior art is being input to
the output circuit by the differential way, the output circuit 50
according to the present invention can also be designed to match
the differential mode. Please refer to FIG. 7. FIG. 7 is a
schematic diagram of an output circuit 60 of another embodiment
according to the present invention. The biggest difference between
FIG. 7 and FIG. 6 is that the input in FIG. 7 inputs the PWM signal
by the differential way, so two sets of the designs as shown in
FIG. 6 also are necessary. Due to the fact that the efficiency of
the elements is almost the same, it will not be described in detail
again.
[0036] As shown in FIG. 7, when the PWM signal being input to the
differential input NI/PI is logic number "0", the differential
output NO/PO connects to the base level input VSS by the transistor
switch M1/M3. However, when the PWM signal being input to the
differential input NI/PI is logic number "1", the transistor switch
M0/M2 is controlled by the negative feedback loop, processed by the
calculation amplifiers 62 and 64 to limit the differential output
NO/PO at the value of the predetermined level input DAO. Therefore,
the predetermined level of the predetermined level input DAO can be
adjusted by the outside volume control to achieve the objective of
adjusting the volume.
[0037] As shown in FIG. 5, the volume control represents an
interface operated by a user such as a volume control turntable or
a volume control key. The interface converts the volume desired by
the user to a corresponding control signal. The control signal
generator 42 receives the volume control and generates a digital
control signal. It has to be emphasized that the interface operated
by the user can be integrated into the control signal generator 42.
The user can control the volume immediately via the interface of
the control signal generator 42. The control signal generator 42
generates the digital control signal for controlling the volume by
the user. The control signal generator 42 is an N bits structure
for generating 2.sup.N kinds of different digital control signals.
The DAC 44 cooperates with the control signal generator 42 to
output 2.sup.N kinds of different predetermined levels to the
predetermined level input DAO according to the digital control
signal.
[0038] Please refer to FIG. 8. FIG. 8 is a schematic diagram of the
control signal generator 42 and the DAC 44 of 4 bits structure
according to the present invention. If N=4, the DAC 44 shown in
FIG. 8 can be obtained. The DAC 44 according to the present
invention comprises a decoder 82, a plurality of analog switches
84, and a plurality of resistances 86. As shown in FIG. 8, The 4
bits digital control signal VC<3:0> generated by the control
signal generator passes through a decoder 82 (4-16 digital decoder
in this embodiment) to obtain 16 level control signals
S<15:0>. Please refer to Table 1. Table 1 is a comparison
table of the digital control signal and the level control signal.
The 16 level control signals S<15:0> is used for controlling
16 analog switches 84. The output level of the predetermined level
input DAO is determined by the level value of VC<3:0> and 16
resistances 86. The 16 resistance values are not necessarily equal.
The necessary resistance value is calculated according to the
practical volume level. For example, the volume adjusting interval
in common use depends on dB value, so that the output voltage of
equal dB value interval can be obtained by combining proper
resistance value.
1 TABLE 1 digital control signal level control signal 0000
0000_0000_0000_0001 0001 0000_0000_0000_0010 0010
0000_0000_0000_0100 0011 0000_0000_0000_1000 0100
0000_0000_0001_0000 0101 0000_0000_0010_0000 0110
0000_0000_0100_0000 0111 0000_0000_1000_0000 1000
0000_0001_0000_0000 1001 0000_0010_0000_0000 1010
0000_0100_0000_0000 1011 0000_1000_0000_0000 1100
0001_0000_0000_0000 1101 0010_0000_0000_0000 1110
0100_0000_0000_0000 1111 1000_0000_0000_0000
[0039] Please refer to FIG. 9. FIG. 9 is a schematic diagram of the
output level of the PWM signal in comparing the prior art and the
present invention. As shown in FIG. 9, PI/NI is differential PWM
according to the prior art, wherein the cycle time of the pulse is
fixed at Ts, the level is fixed at A, and the pulse width changes
with different signals. If the volume is to be reduced by 1/2, the
way of the prior art is to reduce all pulse with (duty) Td by 1/2
immediately. Because the pulse level A doesn't change, the noise is
the same as that before adjusting. Comparatively, the noise sounds
are more obviously, and the audio quality is worse. The present
invention adjusts the output level to 1/2 to reduce the noise as
the volume is reduced, and hence to allow better audio quality.
[0040] As mentioned above, the present invention adjusts volume by
adjusting the output level of the PWM signal instead of by the
conventional method to adjust volume by adjusting the pulse width
of the PWM signal to improve the prior art. Therefore, the method
of controlling the volume according to the present invention can
avoid the disadvantage of enlarging the noise to signal ratio of
the prior art and achieve the objective of improving the audio
quality.
[0041] With the example and explanations above, the features and
spirits of the invention are hopefully well described. Those
skilled in the art will readily observe that numerous modifications
and alterations of the device may be made while retaining the
teaching of the invention. Accordingly, the above disclosure should
be construed as limited only by the meters and bounds of the
appended claims.
* * * * *