Coded data generation or conversion – Analog to or from digital conversion – Differential encoder and/or decoder
Reexamination Certificate
2001-05-22
2004-03-02
Jeanglaude, Jean (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Differential encoder and/or decoder
C341S155000
Reexamination Certificate
active
06700518
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a digital switching amplifier capable of amplifying 1-bit conversion signal, with high efficiency, that is obtained by converting an analog signal or a multi-bit signal in accordance with the delta sigma modulation.
DESCRIPTION OF RELATED ART
A 1-bit signal is obtained by the delta sigma modulation is not limited to be used for recording an audio signal and transmitting among the electronic devices. It is also possible to obtain a demodulated analog signal that has been subjected to the power amplification, only by (a) sending the 1-bit signal, as it is, to a semiconductor power amplifier device so as to obtain switching pulses having a great amplitude of voltage and (b) filtering the switching pulses through a low pass filter.
Further, in the semiconductor power amplifier device a nonlinear region (a saturated region) is used for its operations, unlike the conventional amplifier in which a linear region (an unsaturated region) is used for its operations. Accordingly, the switching amplifier adopting the foregoing delta sigma modulation has the advantage that the power amplification can be made with extremely high efficiency. Because of this, the product adopting the switching amplifier has been commercialized.
The following description deals with one example of a structure of a conventional digital switching amplifier adopting the delta sigma modulation with reference to FIG.
5
.
A conventional digital switching amplifier
10
, as shown in
FIG. 5
, is mainly provided with adders
5
P and
5
M, a delta sigma modulation circuit
1
, a constant voltage switching circuit
2
, a low pass filter (LPF) network circuit
3
, and an attenuation and adjustment section
9
.
Differential input signals are inputted via input terminals
4
P and
4
M to the digital switching amplifier
10
. The differential input signals are made of a pair of an analog acoustic signal S
1
P having a positive polarity and an analog acoustic signal S
1
M having a negative polarity. The delta sigma modulation circuit
1
converts the analog acoustic signals S
1
P and S
1
P into 1-bit signals S
2
P and S
2
M, respectively. Then, the 1-bit signals S
2
P and S
2
M are sent to the constant voltage switching circuit
2
in which constant voltages (+V and −V) are switched and amplified in accordance with the 1-bit signals S
2
P and S
2
M so as to be demodulated to analog acoustic signals by the low pass filter network circuit
3
and to be outputted via output terminals
8
P and
8
M, respectively. Note that the analog acoustic signal S
1
M having a negative polarity is obtained by reversing the polarity of the analog acoustic signal S
1
P having a positive polarity.
Inputted to the attenuation and adjustment section
9
are output signals S
3
P and S
3
M, of the constant voltage switching circuit
2
, that are obtained by the procedure in which the 1-bit signals have been subjected to the power amplification. Inputted to the adders
5
P and
5
M are the analog acoustic signals S
1
P and S
1
M that have been inputted via the input terminals
4
P and
4
M, respectively, as well as negative feedback signals S
4
P and S
4
M from the constant voltage switching circuit
2
. The adders
5
P and
5
M carry out the addition of the signals thus received. Output signals of the adders
5
P and
5
M are sent to the delta sigma modulation circuit
1
.
The negative feedback signals S
4
P and S
4
M are subtracted from the analog acoustic signals S
1
P and S
1
M, respectively, and the result thus subtracted are subjected to the delta sigma modulation by the delta sigma modulation circuit
1
so as to generate the 1-bit signals S
2
P and S
2
M and output them to the constant voltage switching circuit
2
, respectively.
The delta sigma modulation circuit
1
is provided with an integrator and adder group
11
and a quantization circuit
12
. The integrator and adder group
11
includes high-order integrators, and the respective subtracted results are integrated and added. The results thus added are sent to the quantization circuit
12
, respectively. The quantization circuit
12
judges the polarity of the output signals of the integrator and adder group
11
, and converts the results thus judged into 1-bit signals S
2
P and S
2
M, respectively. Note that the quantization threshold of the quantization circuit
12
is set so as to be optimal to a sampling frequency that is to be assumed.
The quantization circuit
12
operates in accordance with a clock signal (not shown). Connected with the constant voltage switching circuit
2
are (a) a constant voltage power source
6
H that outputs a D.C. constant voltage +V having a positive polarity and (b) a constant voltage power source
6
L that outputs a D.C. constant voltage −V having a negative polarity whose amplitude is same as that of the D.C. voltage +V. In the constant voltage switching circuit
2
, the constant voltages +V and −V, which are supplied by the respective constant voltage power sources
6
H and
6
L, are switched in accordance with the 1-bit signals S
2
P and S
2
M, respectively.
Namely, the constant voltage switching circuit
2
amplifies the 1-bit signals S
2
P and S
2
M by using these signals as switching control signals. The constant voltage switching circuit
2
amplifies the 1-bit signals S
2
P and S
2
M and outputs the amplified results to the low pass filter network circuit
3
and the attenuation and adjustment section
9
. The attenuation and adjustment section
9
is provided for attenuating and adjusting the 1-bit signals S
3
P and S
3
M that have been subjected to the power amplification and for returning to the delta sigma modulation circuit
1
by the negative feedback.
The low pass filter network circuit
3
limits to the band width of the lower frequency band so as to demodulate the 1-bit signals S
3
P and S
3
M to the analog acoustic signals, respectively. Further, the low pass filter network circuit
3
outputs the analog acoustic signals via the output terminals
8
P and
8
M, respectively.
The following description deals with the operation of the digital switching amplifier
10
. From the analog acoustic signals S
1
P and S
1
M inputted via the input terminals
4
P and
4
M the negative feedback signals S
4
P and S
4
M are subtracted by the respective adders
5
P and
5
M, and then the subtracted results ((S
1
P−S
4
P) and (S
1
M−S
4
M)) are sent to the delta sigma modulation circuit
1
so as to be subjected to the delta sigma modulation and be converted into the 1-bit signals S
2
P and S
2
M. In the delta sigma modulation circuit
1
, the output signals of the adders
5
P and
5
M are integrated by the integrator and adder group
11
and are added so as to be noise-shaped and be outputted to the quantization circuit
12
which judges the polarity of the added differential integration signals to be converted into binary 1-bit signals S
2
P and S
2
M.
The 1-bit signals S
2
P and S
2
M are sent to the constant voltage switching circuit
2
as the switching control signal, respectively, and are subjected to the power amplification so as to be signals having a voltage range between the constant voltages +V and −V that have been supplied from the constant voltage power sources
6
H and
6
L, respectively. The 1-bit signals S
3
P and S
3
M that have been subjected to the power amplification by the constant voltage switching circuit
2
are sent to the low pass filter network circuit
3
so as to be demodulated to the analog acoustic signals and to be outputted outside via the output terminals
8
P and
8
M, respectively. The 1-bit signals S
3
P and S
3
M that have been subjected to the power amplification are returned by the negative feedback to the delta sigma modulation circuit
1
via the attenuation and adjustment section
9
and the respective adders
5
P and
5
M.
By the way, according to the foregoing conventional digital switching amplifier
10
, the analog acoustic signal outputted via the output termin
Birch & Stewart Kolasch & Birch, LLP
Jeanglaude Jean
Sharp Kabushiki Kaisha
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