U.S. patent application number 10/676950 was filed with the patent office on 2005-04-07 for system of multi-channel shared resistor-string digital-to-analog converters and method of the same.
Invention is credited to Cheng, Eric, Lu, Hipolk, Shieh, Wen-Lung, Tseng, Chih-Hung.
Application Number | 20050073453 10/676950 |
Document ID | / |
Family ID | 34274785 |
Filed Date | 2005-04-07 |
United States Patent
Application |
20050073453 |
Kind Code |
A1 |
Cheng, Eric ; et
al. |
April 7, 2005 |
SYSTEM OF MULTI-CHANNEL SHARED RESISTOR-STRING DIGITAL-TO-ANALOG
CONVERTERS AND METHOD OF THE SAME
Abstract
System of multi-channel shared resistor-string digital-to-analog
converters comprises a time-sharing interpolator converting the
multi-channel digital audio input at low sample rate to the
multi-channel digital audio output at high sample rate, a
time-sharing sigma-delta modulator modulating the multi-channel
digital audio input with a long sample wordlength from the
interpolator to be a multi-channel digital audio output with a
shorter sample wordlength, multi-channel shared resistor-string
digital-to-analog converters converting the multi-channel digital
audio input to be a multi-channel staircase analog signal output,
and one low-order RC filter for each channel further attenuating
the out-of-band noise in the analog staircase analog output,
especially the high-frequency residue images.
Inventors: |
Cheng, Eric; (Taipei,
TW) ; Shieh, Wen-Lung; (Taipei, TW) ; Tseng,
Chih-Hung; (Taipei, TW) ; Lu, Hipolk; (Taipei,
TW) |
Correspondence
Address: |
PERKINS COIE LLP
PATENT-SEA
P.O. BOX 1247
SEATTLE
WA
98111-1247
US
|
Family ID: |
34274785 |
Appl. No.: |
10/676950 |
Filed: |
October 1, 2003 |
Current U.S.
Class: |
341/154 ;
341/143 |
Current CPC
Class: |
H03M 3/50 20130101 |
Class at
Publication: |
341/154 ;
341/143 |
International
Class: |
H03M 001/78; H03M
003/00 |
Claims
1. A system of multi-channel shared resistor-string
digital-to-analog converters (DACs) comprising: a multi-channel
shared resistor-string digital-to-analog converters for converting
multi-channel digital audio input to a multi-channel analog audio
output; and a plurality of high-order low-pass filters for
attenuating the residue images of out-of-band noise in said
multi-channel analog audio output, thereby reconstructing said
multi-channel analog audio output.
2. The system of claim 1, wherein said multi-channel analog audio
signal output includes a multi-channel analog staircase waveform
outputs, and said plurality of high-order low-pass filters includes
plurality of high-order RC filters.
3. The system of claim 1, wherein said multi-channel shared
resistor-string digital-to-analog converters comprises: a shared
resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2M digital signal; a
plurality of switches connected to said shared resistor string and
said plurality of decoders; and a plurality of buffers for
outputting said selected voltage levels; wherein each of said
plurality of switches corresponds to one voltage level of said
shared resistor string, and only one of said 2M digital signal
turning on one of said corresponding switch and outputting
signal.
4. The system of claim 3, wherein said switch includes MOS or
CMOS.
5. A system of multi-channel shared resistor-string
digital-to-analog converters, comprising: an interpolator for
converting a multi-channel digital audio input at a sample rate
into a multi-channel digital audio output with R multiples of said
input sample rate; a multi-channel shared resistor-string
digital-to-analog converters for converting multi-channel digital
audio input to a multi-channel analog audio output; and a plurality
of high-order low-pass filters for attenuating the residue images
of out-of-band noise in said multi-channel analog audio output,
thereby reconstructing said multi-channel analog audio output.
6. The system of claim 5, wherein said interpolator is a
time-sharing interpolator, and said multi-channel analog audio
signal output is a multi-channel analog staircase waveform outputs,
and said plurality of high-order low-pass filters are a plurality
of first order RC filters.
7. The system of claim 5, wherein said multi-channel shared
resistor-string digital-to-analog converters comprises: a shared
resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2M digital signal; a
plurality of switches connected to said shared resistor string and
said plurality of decoders; and a plurality of buffers for
outputting said selected voltage levels; wherein each of said
plurality of switches corresponds to one voltage level of said
shared resistor string, and only one of said 2M digital signal
turning on one of said corresponding switch and outputting
signal.
8. The system of claim 7, wherein said switch is MOS or CMOS.
9. A system of multi-channel shared resistor-string
digital-to-analog converters, comprising: a time-sharing
interpolator for converting a multi-channel digital audio input at
some sample rate into a multi-channel digital audio output with R
multiples of said input sample rate; a multi-channel shared
resistor-string digital-to-analog converters for converting said
multi-channel digital audio output to a multi-channel analog audio
output; and a plurality of low-order lowpass filters for
attenuating the residue images of out-of-band noise in said
multi-channel analog audio signal to complete said multi-channel
analog audio signal reconstruction output.
10. The system of claim 9, wherein said multi-channel analog audio
signal output is a multi-channel analog staircase waveform outputs,
and said plurality of low-order lowpass filters are plurality of
first order RC filters.
11. The system of claim 9, wherein said multi-channel shared
resistor-string digital-to-analog converters comprises: a shared
resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2M digital signal; a
plurality of switches connected to said shared resistor string and
said plurality of decoders; and a plurality of buffers for
outputting said selected voltage levels; wherein each of said
plurality of switches corresponds to one said voltage level of said
shared resistor string, and one of said 2M digital signal turning
on one of said corresponding switch and then outputting the
signal.
12. The system of claim 11, wherein said switch is MOS or CMOS.
13. A system of multi-channel shared resistor-string
digital-to-analog converters, comprising: an interpolator for
converting a multi-channel digital audio input at a sample rate
into a multi-channel digital audio output with R multiples of said
input sample rate; a modulator for modulating said multi-channel
digital audio output to be a multi-channel digital audio output
with a shorter sample wordlength and high-pass quantization noise;
a multi-channel shared resistor-string digital-to-analog converters
for converting said multi-channel digital audio output to a
multi-channel analog audio output; and a plurality of filters for
attenuating the residue images of out-of-band noise in said
multi-channel analog audio to complete said multi-channel analog
audio reconstruction output.
14. The system of claim 13, wherein said interpolator is a
time-sharing interpolator, said modulator is a time-sharing
sigma-delta modulator, said multi-channel analog audio output is a
multi-channel analog staircase waveform outputs, and said plurality
of filters are plurality of first order RC filters.
15. The system of claim 13, wherein said multi-channel shared
resistor-string digital-to-analog converters comprises: a shared
resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2M digital signal; a
plurality of switches connected to said shared resistor string and
said plurality of decoders; and a plurality of buffers for
outputting said selected voltage levels; wherein each of said
plurality of switches corresponds to one said voltage level of said
shared resistor string, and of one said said 2M digital signal
turning on one of said corresponding switch, then outputting the
signal.
16. A system of multi-channel shared resistor-string
digital-to-analog converters, comprising: a time-sharing
interpolator for converting a multi-channel digital audio input at
a sample rate into a multi-channel digital audio output with R
multiples of said input sample rate; a time-sharing sigma-delta
modulator for modulating said multi-channel digital audio output to
be a multi-channel digital audio output with a shorter sample
wordlength and high-pass quantization noise; a multi-channel shared
resistor-string digital-to-analog converters for converting said
multi-channel digital audio output to a multi-channel analog audio
output; and a plurality of first order low-pass filters for
attenuating the residue images of out-of-band noise in said
multi-channel analog audio to complete said multi-channel analog
audio reconstruction output.
17. The system of claim 16, wherein said multi-channel analog audio
output is a multi-channel analog staircase waveform outputs.
18. The system of claim 16, wherein said multi-channel shared
resistor-string digital-to-analog converters comprises: a shared
resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2M digital signal; a
plurality of switches connected to said shared resistor string and
said plurality of decoders; and a plurality of buffers for
outputting said selected voltage levels; wherein each of said
plurality of switches corresponds to one of said voltage level of
said shared resistor string, and one of said 2M digital signal
turning on one said corresponding switch, then outputting the
signal.
19. The system of claim 18, wherein said switch is MOS or CMOS.
20. An output method of multi-channel shared resistor-string
digital-to-analog converters, comprising: converting a
multi-channel digital audio input at a sample rate into a
multi-channel digital audio output with R multiples of said input
sample rate by an interpolator; modulating said multi-channel
digital audio output to be a multi-channel digital audio output
with a shorter sample word length and high-pass quantization noise;
transforming said multi-channel digital audio output to a
multi-channel analog audio output by using a multi-channel shared
resistor-string digital-to-analog converters to; and attenuating
the residue images of out-of-band noise in said multi-channel
analog audio to complete said multi-channel analog audio
reconstruction output by using a plurality of filters.
21. The output method of claim 20, wherein said interpolator is a
time-sharing interpolator, said modulator is a time-sharing
sigma-delta modulator, said multi-channel analog audio output is a
multi-channel analog staircase waveform outputs, and said plurality
of filters are plurality of first order RC filters.
22. The output method of claim 20, wherein said multi-channel
shared resistor-string digital-to-analog converters comprises: a
shared resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2M digital signal; a
plurality of switches connected to said shared resistor string and
said plurality of decoders; and a plurality of buffers for
outputting said selected voltage levels; wherein each of said
plurality of switches corresponds to one said voltage level of said
shared resistor string, and one of said 2M digital signal turning
on one of said corresponding switch, then outputting the
signal.
23. The output method of claim 22, wherein said switch is MOS or
CMOS.
24. An output method of multi-channel shared resistor-string
digital-to-analog converters, comprising: using an interpolator to
convert a multi-channel digital audio input at some sample rate
into a multi-channel digital audio output with R multiples of said
input sample rate; using a multi-channel shared resistor-string
digital-to-analog converters to convert said multi-channel digital
audio output to a multi-channel analog audio output; and using a
plurality of low-order low-pass filters to attenuate the residue
images of out-of-band noise in said multi-channel analog audio to
complete said multi-channel analog audio reconstruction output.
25. The output method of claim 24, wherein said interpolator is a
time-sharing interpolator, said multi-channel analog audio output
is a multi-channel analog staircase waveform outputs, and said
plurality of low-order low-pass filters are plurality of first
order RC filters.
26. The output method of claim 24, wherein said multi-channel
shared resistor-string digital-to-analog converters comprises: a
shared resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2M digital signal; a
plurality of switches connected to said shared resistor string and
said plurality of decoders; and a plurality of buffers for
outputting said selected voltage levels; wherein each of said
plurality of switches corresponds to one said voltage level of said
shared resistor string, and one of said 2M digital signal turning
on one of said corresponding switch and outputting the signal.
27. The system of claim 26, wherein said switch MOS or CMOS.
28. An output method of multi-channel shared resistor-string
digital-to-analog converters, comprising: using a multi-channel
shared resistor-string digital-to-analog converters to convert said
multi-channel digital audio input to a multi-channel analog audio
output; and using a plurality of high-order low-pass filters to
attenuate the residue images of out-of-band noise in said
multi-channel analog audio to complete said multi-channel analog
audio reconstruction output.
29. The output method of claim 28, wherein said multi-channel
analog audio signal output is a multi-channel analog staircase
waveform outputs, and said plurality of high-order low-pass filters
are plurality of high-order RC filters.
30. The output method of claim 28, wherein said multi-channel
shared resistor-string digital-to-analog converters comprises: a
shared resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2M digital signal; a
plurality of switches connected to said shared resistor string and
said plurality of decoders; and a plurality of buffers for
outputting said selected voltage levels; wherein each of said
plurality of switches corresponds to one said voltage level of said
shared resistor string, and one of said 2M digital signal turning
on one of said corresponding switch, then outputting the
signal.
31. The system of claim 30, wherein said switch is MOS or CMOS.
Description
TECHNICAL FIELD
[0001] The present invention relates to a multi-channel audio
digital to analog converters, and specifically, to a system of
high-resolution multi-channel shared resistor-string
digital-to-analog converters and the method of the same.
BACKGROUND
[0002] In the field of digital-to-analog conversion technology for
audio, the conversion rate is typically low, however, the accuracy
requirement is getting more and more stringent. The audio
application specifications demand multi-channel playback much more
than before. Therefore, it is a task to achieve the purpose of
accuracy and multi-channel output performance while maintain the
product competitiveness (low cost).
[0003] The most important considerations under the accuracy
specifications include the dynamic range (DR) and the signal to
noise plus distortion ratio (SNDR). The dynamic range (DR) is
defined as a measurement of the noise generated from the
digital-to-analog converters, and the
signal-to-noise-plus-disortion ratio (SNDR) is indicated as a
measurement of converters linearity. There are several of
digital-to-analog converters. According to the classification of
conversion rate, there are two types of the devices, one is
Nyquist-rate converters and another one is over-sampled
converters.
[0004] In the Nyquist-rate converters, one of the straightforward
implantation is so called resistor string voltage division DACs
(digital-to-analog converters), another way is resistor string
DACs. The primary drawback of the resistor string DACs is that the
string resistor matching is limited by the VLSI technology. The
resistance mismatch of the string resistor is caused by the process
deviation and it will directly influence the voltage division
accuracy of the resistor string. The incorrect voltage division
will cause poor performance on the SNDR in the resistor string
DACs. Therefore, the resistor string DACs is seldom employed in the
conventional high resolution DAC.
[0005] However, resistor string DAC has some advantages. One of the
advantages is that the device has the capability to provide high
dynamic range (DR). The primary noise source of the resistor string
DACs arises mainly from the resistor string thermal noise, switch
and output buffer thermal noise and 1/f noise. Hence, its noise
floor is extremely low and the characteristic of dynamic range (DR)
is excellent. The further benefit for the resistor string DACs is
that the device can be operated at high speeds, thereby achieving
the facility of high sample rate conversion application.
[0006] The major over-sampled digital-to-analog converter is the
Sigma-delta digital-to-analog converter, and the device shares a
big marketing.
[0007] FIG. 1 shows a block diagram for typical single channel
sigma-delta DAC (digital-to-analog converter) in accordance with
the prior art. The binary digit of the input could be N bits (N may
be 16,18,20,24) Nyquist-rate PCM digital audio source. The sample
rate F.sub.N.sub..sub.13in is interpolated by an interpolator 100
to increase the sampling rate to R times, namely,
RF.sub.N.sub..sub.--in. The N bits RF.sub.N.sub..sub.--in data is
then reduced the wordlength to M-bit per sample by a sigma-delta
modulator 110, M is smaller than N, the quantization noise
generated during the procedure will be shifted to the high
frequency outside the baseband via the loop.
[0008] The M-bits output of the sigma-delta modulator 110 is
subsequently transformed to a staircase analog signal by M-bits
digital-to-analog converters. Finally, the staircase analog signal
is filtered out-of-band noise by a switched-capacitor low-pass
filter 130 and a continuous-time low-pass filter 140, thereby
reconstructing the analog audio signal. However, 1-bit sigma-delta
digital-to-analog converters prone to instability and high clock
rate issue that cause application limitation on the DAC
applications that require high resolution and high bandwidth.
[0009] Further, substantial out-of-band quantization noise is
generated during the sigma-delta modulator stage such that the
digital-to-analog converters output need high-order low-pass
filters to filter out such noise to sufficient low to avoid slewing
phenomenon generated by the audio amplifier, thereby inducing the
inter-modulation and harmonic distortion. As known, those will
influence the output quality, seriously. Multi-bit sigma-delta
digital-to-analog converters (including MASH DACs) can resolve
aforementioned instability, high clock rate issue and reduce the
stage required on the low-pass post-filter.
[0010] In general, the bit number of the multi-bit sigma-delta DAC
is less than 5 bits (including 5 bits) after the modulation by a
sigma-delta modulation, and therefore, the SCF stage for extremely
high level out-of-band quantization noise power can not be omitted.
The low-noise SCF design becomes the key for overall performance of
sigma-delta DACs.
[0011] Moreover, in multi-channel applications, the SCF of
traditional sigma-delta DAC is unlikely to be used mutually, so
that how to reduce the cost to increase competitiveness is an
issue.
[0012] In view of above description, the present invention provides
a system and output method of novel multi-channel audio DACs.
SUMMARY
[0013] The present invention provides a system of multi-channel
shared resistor-string digital-to-analog converters, comprising: an
interpolator for converting a multi-channel digital audio input at
a sample rate into a multi-channel digital audio output with R
multiples of the input sample rate; a modulator for modulating the
multi-channel digital audio output to be a multi-channel digital
audio output with a shorter sample wordlength and high-pass
quantization noise; a multi-channel shared resistor-string
digital-to-analog converters for converting the multi-channel
digital audio output to a multi-channel analog audio output; and a
plurality of filters for attenuating the residue images of
out-of-band noise in the multi-channel analog audio to complete the
multi-channel analog audio reconstruction output.
[0014] Wherein the interpolator is a time-sharing interpolator, the
modulator is a time-sharing sigma-delta modulator, the
multi-channel analog audio output is a multi-channel analog
staircase waveform outputs, and the plurality of filters are
plurality of first order RC filters. The multi-channel shared
resistor-string digital-to-analog converters comprises: a shared
resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2.sup.M digital signal; a
plurality of switches connected to the shared resistor string and
the plurality of decoders; and a plurality of buffers for
outputting the selected voltage levels; wherein each of the
plurality of switches corresponds to one the voltage level of the
shared resistor string, and of one the 2.sup.M digital signal
turning on one of the corresponding switch, then outputting the
signal.
[0015] The system of multi-channel shared resistor-string
digital-to-analog converters, comprising: a time-sharing
interpolator for converting a multi-channel digital audio input at
a sample rate into a multi-channel digital audio output with R
multiples of the input sample rate; a time-sharing sigma-delta
modulator for modulating the multi-channel digital audio output to
be a multi-channel digital audio output with a shorter sample
wordlength and high-pass quantization noise; a multi-channel shared
resistor-string digital-to-analog converters for converting the
multi-channel digital audio output to a multi-channel analog audio
output; and a plurality of first order low-pass filters for
attenuating the residue images of out-of-band noise in the
multi-channel analog audio to complete the multi-channel analog
audio reconstruction output.
[0016] Wherein the multi-channel analog audio output is a
multi-channel analog staircase waveform outputs. The multi-channel
shared resistor-string digital-to-analog converters comprises: a
shared resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2.sup.M digital signal; a
plurality of switches connected to the shared resistor string and
the plurality of decoders; and a plurality of buffers for
outputting the selected voltage levels; wherein each of the
plurality of switches corresponds to one of the voltage level of
the shared resistor string, and one of the 2.sup.M digital signal
turning on one the corresponding switch, then outputting the
signal.
[0017] The present invention discloses an output method of
multi-channel shared resistor-string digital-to-analog converters,
comprising:
[0018] converting a multi-channel digital audio input at a sample
rate into a multi-channel digital audio output with R multiples of
the input sample rate by an interpolator;
[0019] modulating the multi-channel digital audio output to be a
multi-channel digital audio output with a shorter sample wordlength
and high-pass quantization noise;
[0020] transforming the multi-channel digital audio output to a
multi-channel analog audio output by using a multi-channel shared
resistor-string digital-to-analog converters to; and
[0021] attenuating the residue images of out-of-band noise in the
multi-channel analog audio to complete the multi-channel analog
audio reconstruction output. Wherein the multi-channel shared
resistor-string digital-to-analog converters comprises: a shared
resistor string for providing voltage levels of each channel
demand; a plurality of decoders for receiving a M bits modulated
digital input signal and then outputting 2.sup.M digital signal; a
plurality of switches connected to the shared resistor string and
the plurality of decoders; and a plurality of buffers for
outputting the selected voltage levels; wherein each of the
plurality of switches corresponds to one the voltage level of the
shared resistor string, and one of the 2.sup.M digital signal
turning on one of the corresponding switch, then outputting the
signal.
[0022] An output method of multi-channel shared resistor-string
digital-to-analog converters, comprising:
[0023] using an interpolator to convert a multi-channel digital
audio input at some sample rate into a multi-channel digital audio
output with R multiples of the input sample rate;
[0024] using a multi-channel shared resistor-string
digital-to-analog converters to convert the multi-channel digital
audio output to a multi-channel analog audio output; and
[0025] using a plurality of low-order low-pass filters to attenuate
the residue images of out-of-band noise in the multi-channel analog
audio to complete the multi-channel analog audio reconstruction
output.
[0026] Wherein the interpolator is a time-sharing interpolator, the
multi-channel analog audio output is a multi-channel analog
staircase waveform outputs, and the plurality of low-order low-pass
filters are plurality of first order RC filters. Wherein the
multi-channel shared resistor-string digital-to-analog converters
comprises: a shared resistor string for providing voltage levels of
each channel demand; a plurality of decoders for receiving a M bits
modulated digital input signal and then outputting 2.sup.M digital
signal; a plurality of switches connected to the shared resistor
string and the plurality of decoders; and a plurality of buffers
for outputting the selected voltage levels; wherein each of the
plurality of switches corresponds to one the voltage level of the
shared resistor string, and one of the 2.sup.M digital signal
turning on one of the corresponding switch and outputting the
signal.
[0027] The present invention also provides an output method of
multi-channel shared resistor-string digital-to-analog converters,
comprising:
[0028] using a multi-channel shared resistor-string
digital-to-analog converters to convert the multi-channel digital
audio input to a multi-channel analog audio output; and
[0029] using a plurality of high-order low-pass filters to
attenuate the residue images of out-of-band noise in the
multi-channel analog audio to complete the multi-channel analog
audio reconstruction output.
[0030] Wherein the interpolator is a time-sharing interpolator, the
multi-channel analog audio signal output is a multi-channel analog
staircase waveform outputs, and the plurality of high-order
low-pass filters are plurality of high-order RC filters. The
multi-channel shared resistor-string digital-to-analog converters
comprises: a shared resistor string for providing voltage levels of
each channel demand; a plurality of decoders for receiving a M bits
modulated digital input signal and then outputting 2.sup.M digital
signal; a plurality of switches connected to the shared resistor
string and the plurality of decoders; and a plurality of buffers
for outputting the selected voltage levels; wherein each of the
plurality of switches corresponds to one the voltage level of the
shared resistor string, and one of the 2.sup.M digital signal
turning on one of the corresponding switch, then outputting the
signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
becomes better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0032] FIG. 1 is a system diagram of typical single channel
sigma-delta digital-to-analog converters in accordance with the
prior art.
[0033] FIG. 2 is a system diagram of multi-channel shared
resistor-string digital-to-analog converters in accordance with the
present invention.
[0034] FIG. 3 is a system diagram of multi-channel shared
resistor-string digital-to-analog converters in accordance with the
present invention.
[0035] FIG. 4 is a system diagram of multi-channel shared
resistor-string digital-to-analog converters in accordance with the
present invention.
[0036] FIG. 5 is a comparison diagram of out-of-band quantization
noise power between sigma-delta modulator of conventional
sigma-delta digital-toanalog- converters and sigma-delta modulator
of the present invention.
[0037] FIG. 6 is a scheme of multi-channel shared resistor-string
digital-to-analog converters in accordance with the present
invention.
[0038] FIG. 7 is a scheme of the residue images of multi-channel
analog staircase waveform outputs at integral multiple oversampling
rate in accordance with the present invention.
DETAILED DESCRIPTION
[0039] FIG. 2 is a system diagram of multi-channel shared
resistor-string DACs (digital-to-analog converters) in accordance
with the present invention. Turning to FIG. 2, a multi-channel
shared resistor-string digital-to-analog converters 200 are used
for converting the multi-channel digital audio output to a
multi-channel analog audio output. In practical applications, the
shared resistor string may use multiple resistor strings to reduce
the resistor number. For example, 16 bits shared resistor string
DACs, the shared resistor string can separate two resistor strings
including 256 number resistors, and therefore the total number
resistors are 512. In the present invention, the shared resistor
string needs only single resistor string, therefore it can reduce
substantially area of the multi-channel resistor-string.
[0040] Moreover, pluralities of high-order low-pass filters 210 are
used to attenuate the residue images of out-of-band noise in the
multi-channel analog audio output in order to complete the
multi-channel analog audio output reconstruction. The high-order
low-pass filter 210 includes a high-order RC filter 210.
[0041] FIG. 3 is another preferred system diagram of multi-channel
shared resistor-string digital-to-analog converters in accordance
with the present invention. The time-sharing interpolator 220 is
used to interpolate a multi-channel digital audio input. The sample
wordlength of the multi-channel digital audio input may be
16,18,20,22,24 or required bit number of other high-resolution
audio standard. The sample ratio F.sub.N.sub..sub.--in of the
multi-channel digital audio input is converted into a multi-channel
digital audio output at R times of the input sample rate
(RF.sub.N.sub..sub.--in), which is interpolated by the time-sharing
interpolator 220. The output sample wordlength remains slightly
longer than or equal to the input sample wordlength. It can
decrease the level of the matching requirements for the
multi-channel shared resistor-string DACs by the usage of the
oversampling.
[0042] The multi-channel shared resistor-string DACs 230 are
utilized to convert the multi-channel digital audio output to a
multi-channel analog staircase waveform outputs. In practical
applications, the shared resistor-string may include the multiple
resistor strings to reduce the resistor number. Take the 16-bits
shared resistor-string digital-to-analog converters as an example,
the shared resistor-string can separate into two resistor-string
including 256 resistors, and therefore the total number of the
resistors is 512. In the present invention, the required shared
resistor-string of the multi-channel resistor-string DACs is only
single one resistor-string. Therefore, the present invention may
reduce substantially area of the multi-channel resistor-string.
[0043] Furthermore, pluralities of low-order low-pass filters 240
are used to attenuate the residue images of out-of-band noise in
the multi-channel analog audio input, thereby reconstructing the
multi-channel analog audio reconstruction output. The low-order
low-pass filter 240 includes a low-order RC filter 240.
[0044] FIG. 4 is yet another system diagram of multi-channel shared
resistor-string digital-to-analog converters in accordance with the
present invention. The time-sharing interpolator 300 is used to
interpolate a multi-channel digital audio input. The sample
wordlength of the multi-channel digital audio input may be
16,18,20,22,24 or required bit number of other high-resolution
audio standard. The sample ratio F.sub.N.sub..sub.--in of the
multi-channel digital audio input is converted into R times of the
initial input sample rate RF.sub.N.sub..sub.--in by the
time-sharing interpolator 300. The output sample wordlength will
remains slightly longer than or equal to the input sample
wordlength. As mentioned, the matching requirements will be
reduced.
[0045] The time-sharing sigma-delta modulator 310 is used to
modulate the multi-channel channel digital audio input that is
interpolated by time-sharing interpolator 300 to a multi-channel
digital audio output having shorter sample wordlength and high-pass
quantization noise. The time-sharing sigma-delta modulator 310
re-quantize the N bits sample rate RF.sub.N.sub..sub.--in
multi-channel digital audio input to a M bits sample rate
RF.sub.N.sub..sub.--in multi-channel digital audio output from the
time-sharing interpolator 300, wherein M is smaller than N. The
quantization noise created in the re-quantization process may be
modulated to high frequency via a loop for maintaining the low
noise and low harmonic distortion on baseband.
[0046] In general, the output bit number of sigma-delta modulator
is less than 5 bits (including 5 bits), and the bit number of the
sigma-delta modulator 310 output may reach 10.about.14 bits. It
assumes that the number of the output bit for the sigma-delta
modulator 310 is 12 bits and the noise transfer function of the
sigma-delta modulator 310 is (1-z.sup.-1).sup.2, and therefore the
out-of-band quantization noise power created by the sigma-delta
modulator 310 is smaller than -71 dB (-6.02*12-1.76+3 dB) relative
to the full-scale sinusoidal input power. The out-of-band
quantization noise power created by conventional sigma-delta DACs
modulator, for example sigma-delta modulator stage output 5 bits,
is approximately -28 dB (-6.02*5-1.76+3 dB).
[0047] FIG. 5 is a comparison diagram of out-of-band quantization
noise power between sigma-delta modulator of conventional
sigma-delta DACs and the present invention. The area covered from
the solid line to the horizontal axis indicates the out-of-band
quantization noise power created by the sigma-delta modulator 310
according to the present invention. Similarly, the region from the
dot line to the horizontal axis represents the out-of-band
quantization noise power generated by the output of the
conventional sigma-delta DACs. Although the sigma-delta modulation
310 is incorporated into the present invention as the intermediate
stage to lower the sample wordlength, however, the output still
maintains 10-14 bits. Hence, the out-of-band quantization noise
keeps in extremely low level to omit the SCF stage required by the
conventional sigma-delta DACs. The sigma-delta modulation 310 may
only reduce fewer bits such that it can lower the order and
oversampling ratio of the sigma-delta modulation 310 and it may
considerably provide the function of time-sharing.
[0048] The multi-channel shared resistor-string digital-to-analog
converters 320 can convert the multi-channel digital audio input
modulated by the sigma-delta modulation 310 to a multi-channel
analog staircase outputs, as shown in FIG. 4. That is to say, the
multi-channel digital audio input that is modulated by the
sigma-delta modulation 310 is converted into a multi-channel analog
staircase outputs by the multi-channel shared resistor-string
digital-to-analog converters 320. The multi-channel shared
resistor-string digital-to-analog converters 320 includes a shared
resistor string, a plurality of decoders, a plurality of switches
and a plurality of buffers.
[0049] In one embodiment, the output of the sigma-delta modulation
310 is 3 bits (in practice, the output is 10.about.14 bits), and
the present invention introduces the p channels 3 bits shared
resistor-string DACs as shown in FIG. 6. The resistors
500,510,520,530,540,550,560 and 570 may provide a series of voltage
levels that can be shared in the p-channels shared resistor-string
DACs. The decoder 580 of the first channel receives modulated 3
bits digital input signal, and then outputs 8 digital signals. One
of the 8 digital signals is responsive to turn on the correspondent
switch, such as switches 590,600,610,620,630,640,650 or 660. The
digital signal that makes the switch to open will output an analog
staircase waveform through a buffer 670 by a correspondent voltage
level of the shared resistor string. The switch
590,600,610,620,630,640,6- 50 or 660 is, for example, a MOS or CMOS
switch.
[0050] Moreover, the decoder 680 of the p channel receives
modulated 3 bits digital input signal. Subsequently, it outputs 8
digital signals. One of the digital signals will also turn on the
correspondent switch, such as switches 690,700,710,720,730,740,750
or 760. As aforementioned, the digital signal outputs an analog
staircase waveform through a buffer 770 via the shared resistor
string. Similarly, the switch 690,700,710,720,730,740,750 or 760
is, for example, a MOS or CMOS switch.
[0051] In one current practical application, the shared
resistor-string in FIG. 6 may use multiple resistor strings to
reduce the number of the resistor. Take the 12-bits shared
resistor-string DACs as an example, the shared resistor-string can
be separated into two resistor-string including 64 resistors. The
total number of the resistors is 128. In the present invention, the
required shared resistor-string of the multi-channel
resistor-string DACs is only single resistor-string. Apparently, it
can reduce substantially the area of the multi-channel
resistor-string. Furthermore, the poor linearity issue can be
improved by enlarging the area of the shared resistor-string and
employing the over-sampling techniques. The enlarged area of the
shared resistor-string can improve the resistor string voltage
division accuracy by reducing relative random geometry errors in
process. Moreover, the usage of the over-sampling techniques
distributes the power of harmonic distortion generated by the
string resistor mismatches issue to the wider bandwidth, thereby
improving the THD performance in the baseband.
[0052] The power of the out-of-band quantization noise is extremely
low in the analog staircase waveform outputs by using the
multi-channel shared resistor-string DACs 320 due to the
sigma-delta modulation 310 maintains 10.about.14 bits outputs, so
that the analog audio signal reconstruction needs to consider the
images at the multiple sample frequency, only. The images will be
filtered below to a certain level through a sample-and-hold
function of the multi-channel shared resistor-string DACs 320,
please refer to FIG. 7. Take 48 kHz digital audio as an example,
assume that the base-band bandwidth is 0.about.20 kHz, the images
minimum attenuation caused by the sample-and-hold function in
different over-sampling ratio is shown in table one. From table.1,
the images minimum attenuation is 37.60 dB when the over-sampling
ratio is 32.
1 TABLE 1 Oversampling Ratio 8 16 32 64 128 Min. Attenuation 25.24
31.47 37.60 43.67 49.72 (dB)
[0053] Finally, the analog staircase outputs of each channel are
processed by a low-order RC filters 330 to further attenuate the
residue images, as shown in FIG. 4. The low-order RC filters 330,
for example, are the first-order RC filters 330. It needs an
extremely high over-sampling ratio to avoid back level entering
slewing mode via the sample-and-hold function to filter out the
images to a sufficient low level. Therefore, it needs to introduce
the low-order low-pass filters for filtering out the residue images
by the sample-and-hold function to a sufficient low level. The
simple RC filter can be used under such condition of that the
over-sampling ratio is high enough to separate the images far from
base-band. In one embodiment, 32 over-sampling ratio is used by 48
kHz digital audio along with a first-order RC filter with -3 dB at
48 kHz. The images minimum attenuation is 67.70 dB. Apparently, it
is capable to filter out the images by using the sample-and-hold
function of the multi-channel shared resistor-string DACs 320.
[0054] The advantage of the present invention includes the
following description:
[0055] 1. One voltage division resistor-string are shared by the
multi-channel resistor-string voltage division digital-to-analog
converters, thereby reducing the area occupied by the conventional
manner.
[0056] 2. It can reduce the resistor-string number of the shared
resistor-string DACs through Over-sampling ratio and sigma-delta
modulation techniques. Further, it reduces the area of the resistor
to reduce the complexities of the routing issue when sharing the
resistor string in the field of high-resolution multi-channel
applications.
[0057] 3. By introducing the over-sampling ratio, the requirement
for the resistor string matching can be reduced.
[0058] 4. The required number of resistor string had slashed
through the usage of the shared resistor-string and the sigma-delta
modulation techniques, therefore, the insufficient resistor-string
voltage division accuracy in process variations can be overcame by
increasing the area of each resistor string.
[0059] 5. The requirement of the switched-capacitor filters of
typical sigma-delta DACs can be omitted due to the high-bit outputs
of the sigma-delta modulation techniques.
[0060] 6. The lower digital time-pulse frequency and the shared
resistor-string can reduce the power dissipation consumed by the
resistor-string.
[0061] 7. The high frequency residue images can be filtered out by
the usage of the low-order RC filters, for example the first-order
lowpass RC filters.
[0062] As is understood by a person skilled in the art, the
foregoing preferred embodiments of the present invention are
illustrated of the present invention rather than limiting of the
present invention. It is intended to cover various modifications
and similar arrangements included within the spirit and scope of
the appended claims, the scope of which should be accorded the
broadest interpretation so as to encompass all such modifications
and similar structure. While the preferred embodiment of the
invention has been illustrated and described, it will be
appreciated that various changes can be made therein without
departing from the spirit and scope of the invention.
* * * * *