U.S. patent application number 15/459376 was filed with the patent office on 2018-01-25 for audiovisual signal processing circuit and associated television signal processing method.
The applicant listed for this patent is MStar Semiconductor, Inc.. Invention is credited to JUNG-KUEI CHANG, Chih-Ching Chao, Ying-Chao Chou, Ching-Fu Lan, HUANG-HSIANG LIN.
Application Number | 20180027277 15/459376 |
Document ID | / |
Family ID | 60989002 |
Filed Date | 2018-01-25 |
United States Patent
Application |
20180027277 |
Kind Code |
A1 |
Lan; Ching-Fu ; et
al. |
January 25, 2018 |
AUDIOVISUAL SIGNAL PROCESSING CIRCUIT AND ASSOCIATED TELEVISION
SIGNAL PROCESSING METHOD
Abstract
A television signal processing circuit includes an audio/video
(AV) signal generating circuit, an intermediate frequency (IF)
mixer, a first filter, a radio-frequency (RF) mixer, a second
filter and a digital-to-analog converter (DAC). The AV signal
generator generates a digital AV signal. The IF mixer converts the
digital AV signal to an IF AV signal. The first filter filters the
IF AV signal to generate a filtered IF AV signal. The RF mixer
converts the filtered IF AV signal to an RF AV signal. The second
filter filters the RF AV signal to generate a filtered RF AV
signal. The DAC converts the filtered RF AV signal to an analog AV
signal and transmits the analog AV signal to an antenna.
Inventors: |
Lan; Ching-Fu; (Hsinchu
County, TW) ; Chou; Ying-Chao; (Hsinchu County,
TW) ; Chao; Chih-Ching; (Hsinchu County, TW) ;
LIN; HUANG-HSIANG; (Hsinchu County, TW) ; CHANG;
JUNG-KUEI; (Hsinchu County, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MStar Semiconductor, Inc. |
Hsinchu Hsien |
|
TW |
|
|
Family ID: |
60989002 |
Appl. No.: |
15/459376 |
Filed: |
March 15, 2017 |
Current U.S.
Class: |
725/151 |
Current CPC
Class: |
H04N 21/439 20130101;
H04N 21/42607 20130101; H04N 21/44 20130101; H04N 7/01
20130101 |
International
Class: |
H04N 21/426 20060101
H04N021/426; H04N 21/44 20060101 H04N021/44; H04N 21/439 20060101
H04N021/439 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 22, 2016 |
TW |
105123148 |
Claims
1. A television signal processing circuit, applied to a set-up box
(STB), comprising: an audio/video (AV) signal generating circuit,
generating a digital AV signal; an intermediate-frequency (IF)
mixer, generating an IF AV signal according to the digital AV
signal; a first filter, filtering the IF AV signal to generate a
filtered IF AV signal; a radio-frequency (RF) mixer, generating an
RF AV signal according to the filtered IF AV signal; a second
filter, filtering the RF AV signal to generate a filtered RF AV
signal; and a digital-to-analog converter (DAC), converting the
filtered RF AV signal to an analog AV signal and transmitting the
analog AV signal to an antenna.
2. The television signal processing circuit according to claim 1,
wherein the first filter is a vestigial-sideband (VSB) filter.
3. The television signal processing circuit according to claim 1,
wherein the second filter is a band-pass filter.
4. The television signal processing circuit according to claim 1,
wherein the filtered IF AV signal is a first filtered IF AV signal,
the television signal processing further comprising: an
interpolation circuit, interpolating the first filtered IF AV
signal to generate a second filtered IF AV signal, and transmitting
the first and second filtered IF AV signal to the RF mixer.
5. The television signal processing circuit according to claim 4,
wherein the RF mixer is a first RF mixer, the television signal
processing circuit further comprising: a second RF mixer; and a
serial-to-parallel converter, transmitting the first and second
filtered RF AV signals to the first and second RF mixers,
respectively.
6. The television signal processing circuit according to claim 1,
further comprising: a sigma-delta modulation circuit, performing a
noise shifting process on the filtered RF AV signal to generate a
processed RF AV signal, and transmitting the processed RF AV signal
to the DAC.
7. The television signal processing circuit according to claim 1,
disposed in the STB.
8. The television signal processing circuit according to claim 7,
wherein a frequency range of the filtered RF AV signal is one of
61.25 MHz and 67.25 MHz.
9. The television signal processing circuit according to claim 7,
wherein a frequency range of the filtered RF AV signal is one of
55.25 Mhz and 63.25 MHz.
10. The television signal processing circuit according to claim 1,
wherein the first filter is a real filter.
11. The television signal processing circuit according to claim 1,
wherein the second filter is a real filter.
12. A television signal processing method, applied to a set-up box
(STB), comprising: generating a digital audio/video (AV) signal;
generating an intermediate-frequency (IF) AV signal according to
the AV signal; filtering the IF AV signal to generate a filtered IF
AV signal; generating a radio-frequency (RF) AV signal according to
the filtered IF AV signal; filtering the RF AV signal to generate a
filtered RF AV signal; and converting the filtered RF AV signal to
an analog AV signal, and transmitting the analog AV signal to an
antenna.
13. The television signal processing method according to claim 12,
wherein the filtered IF AV signal is a first filtered IF AV signal,
the RF AV signal is a first RF AV signal, and the step of
generating the RF AV signal according to the filtered IF AV signal
comprises: interpolating the first filtered IF AV signal to
generate a second filtered IF AV signal; and converting the first
and second filtered IF AV signal to the first RF AV signal and a
second RF AV signal, respectively.
14. The television signal processing method according to claim 12,
wherein the step of converting the filtered RF AV signal to the
analog AV signal comprises: performing a noise shifting process on
the filtered RF AV signal to generate a processed RF AV signal; and
converting the processed RF AV signal to the analog AV signal.
15. The television signal processing method according to claim 12,
wherein a frequency range of the filtered RF AV signal is one of
61.25 MHz and 67.25 MHz.
16. The television signal processing method according to claim 12,
wherein a frequency range of the filtered RF AV signal is one of
55.25 Mhz and 63.25 MHz.
17. The television signal processing method according to claim 12,
wherein the step of filtering the IF AV signal to generate the
filtered IF AV signal comprises: filtering the IF AV signal by a
real vestigial-sideband (VSB) filter to generate the filtered IF AV
signal.
18. The television signal processing method according to claim 12,
wherein the step of filtering the RF AV signal to generate the
filtered RF AV signal comprises: filtering the RF AV signal by a
real band-pass filter to generate the filtered RF AV signal.
Description
[0001] This application claims the benefit of Taiwan application
Serial No. 105123148, filed Jul. 22, 2016, the subject matter of
which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The invention relates in general to signal processing, and
more particularly to a television processing circuit applied to a
set-up box (STB) and an associated television signal processing
method.
Description of the Related Art
[0003] Demands of common households on set-up boxes (STBs) increase
along with the broadcasting of digital televisions. As some older
televisions are not equipped with audio/video (AV) ports for
connecting to the STB, the STB needs an additional set of circuit
designed for transmitting (AV) signals to these older televisions.
In a conventional solution, a digital AV signal is converted to an
analog signal, which is then processed and transmitted. Therefore,
a more complex circuit design is required. For example, a surface
acoustic wave (SAW) filter needs to be designed to filter out
analog radio-frequency (RF) signals, in a way that production
complications and costs are increased.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a
television signal processing circuit disposed in a set-up box
(STB). Main signal processing circuits and a filters in the
television signal processing circuit are implemented by digital
circuits, with the filters having a simpler design structure,
thereby solving issues of the prior art.
[0005] A television signal processing circuit applied to an STB is
disclosed according to an embodiment of the present invention. The
signal processing circuit includes an audio/video (AV) signal
generator, an intermediate-frequency (IF) mixer, a first filter, a
radio-frequency (RF) mixer, a second filter and a digital-to-analog
converter (DAC). The AV signal generator generates a digital AV
signal. The IF mixer generates an IF AV signal according to the
digital AV signal. The first filter filters the IF AV signal to
generated a filtered IF AV signal. The RF mixer generates an RF AV
signal according to the filtered IF AV signal. The second filter
filters the RF AV signal to generate a filtered RF AV signal. The
DAC converts the filtered RF AV signal to an analog AV signal, and
transmits the analog AV signal to an antenna.
[0006] A television signal processing method is disclosed according
to another embodiment of the present invention. The method
includes: generating a digital AV signal; generating an IF AV
signal according to the digital AV signal; filtering the IF AV
signal to generate a filtered IF AV signal; generating an RF AV
signal according to the filtered IF AV signal; filtering the RF AV
signal to generate a filtered RF AV signal; and converting the
filtered RF AV signal to an analog AV signal and transmitting the
analog AV signal to an antenna.
[0007] The above and other aspects of the invention will become
better understood with regard to the following detailed description
of the preferred but non-limiting embodiments. The following
description is made with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a block diagram of a television signal processing
circuit according to an embodiment of the present invention;
[0009] FIG. 2 is a spectrum diagram of a digital audio/video (AV)
signal;
[0010] FIG. 3 is a spectrum diagram of an intermediate-frequency
(IF) signal and a schematic diagram of a frequency that a vestigial
sideband (VSB) filter allows passing;
[0011] FIG. 4 is a spectrum diagram of a radio-frequency (RF)
signal and a schematic diagram of a frequency that a band-pass
filter allows passing;
[0012] FIG. 5 is a block diagram of a television signal processing
circuit according to another embodiment of the present invention;
and
[0013] FIG. 6 is a flowchart of a television signal processing
method according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] FIG. 1 shows a block diagram of a television signal
processing circuit 100 according to an embodiment of the present
invention. As shown in FIG. 1, the television signal processing
circuit 100 includes an audio/video (AV) signal generating circuit
110, an intermediate-frequency (IF) mixer 120, a vestigial sideband
filter 130, a radio-frequency (RF) mixer 140, a band-pass filter
150, a sigma-delta modulation circuit 160 and a digital-to-analog
converter (DAC) 170. In this embodiment, the television signal
processing circuit 100 is a single chip, and is disposed in an
set-up box (STB). Further, the television signal processing circuit
100 generates a plurality of television channel signals having
predetermined frequencies through an antenna of the STB to an
external television. The plurality of television channel signals
having the predetermined frequencies may be signals of the third
and the fourth channels (with frequencies 61.25 MHz and 67.25 MHz,
respectively) defined by the National Television System Committee
(NTSC), or signals of the third and the fifth channels (with
frequencies 55.25 MHz and 63.25 MHz, respectively) defined by the
Progressive Alternating Line (PAL) standard.
[0015] In an operation process of the television signal processing
circuit 100, the AV signal generator 110 receives a digital video
signal and a digital audio signal to generate a digital AV signal
Vin, whose spectrum is as shown in FIG. 2. Even if a digital
television signal received is converted to an analog signal, a
television may not be able to decode the contents in the analog
signal. Therefore, the digital television signal that the STB
receives needs to be first decoded to obtain the video signal and
the audio signal. The video signal and the audio signal are then
re-coded to a digital AV signal Vin according to formats compliant
with the NTSC or PAL standards. The IF mixer 120 converts the
digital AV signal Vin to an intermediate-frequency (IF) AV signal
V.sub.IF by using a local oscillation signal LO1, and the vestigial
sideband filter 130 filers the IF AV signal V.sub.IF to generate a
filtered IF AV signal V.sub.IF'. FIG. 3 shows a spectrum diagram of
the IF AV signal V.sub.IF, with parts framed within the dotted
lines being frequencies that the vestigial sideband filter 130
allows passing. In this embodiment, the center frequencies of the
IF AV signal V.sub.IF are 18.25 MHz and -18.25 MHz. Referring to
FIG. 2, due to the asymmetry in the input signal, a complex filter
is needed to filter out the baseband signals in the parts within
the dotted lines. In contrast, in FIG. 3, the signal is symmetrical
after it is adjusted to the intermediate frequency, and vestigial
sideband filtering may be implemented by real filter, hence
reducing the complexity and production costs of the filter. Next,
the RF mixer 140 converts the filtered IF AV signal V.sub.IF' to an
RF AV signal V.sub.RF by using a local oscillation signal LO2, and
the band-pass filter 150 filters the RF AV signal V.sub.RF to
generate a filtered RF AV signal V.sub.RF'. FIG. 4 shows a spectrum
diagram of the RF AV signal V.sub.RF, with the parts framed within
the dotted lines representing the frequency that the band-pass
filter 150 allows passing. In this embodiment, the center
frequencies of the RF AV signal V.sub.RF are 61.25 MHz and -61.25
MHz. The sigma-delta modulation circuit 160 performs a noise
shifting process on the filtered RF AV signal V.sub.RF' to generate
a process signal V.sub.RF'', and transmits the process signal
V.sub.RF'' to the DAC 170 to be converted to an analog AV signal
Vout. The analog AV signal is then transmitted to a television via
an antenna. The center frequency 61.25 MHz of the RF AV signal
V.sub.RF is the frequency of the third channel defined by the
NTSC.
[0016] The frequency 18.25 MHz shown in FIG. 3 and the frequency
61.25 MHz shown in FIG. 4 are examples for illustration purposes,
and are not to be construed as limitations to the present
invention. In other embodiments, the IF frequency shown in FIG. 3
may have different frequencies according to the planning of a
designer, and the frequency shown in FIG. 4 may also be a frequency
corresponding to a predetermined frequency in other television
standards. For example, the frequency in FIG. 4 may be the
frequency 67.25 MHz of the fourth channel defined by the NTSC, or
the frequencies 55.25 MHz and 63.25 MHz of the third and the fifth
channels defined by the PAL standard.
[0017] In the television signal processing circuit 100 in FIG. 1,
most signal processing units and all of the filter circuits are
implemented by digital circuits, and are integrated in one single
chip, thereby significantly simplifying the circuit structure and
reducing production costs. Further, by adjusting the signal to the
intermediate frequency to perform vestigial sideband filtering, a
real filter having a simpler structure, instead of a SAW filter or
a complex filter, may be adopted in the television signal
processing circuit 100 to further lower design and production
costs.
[0018] FIG. 5 shows a block diagram of a television signal
processing circuit 500 according to another embodiment of the
present invention. As shown in FIG. 5, the television signal
processing circuit 500 includes an AV signal generating circuit
510, an IF mixer 520, a vestigial sideband filter 530, an
interpolation circuit 534, a serial-to-parallel converter 536,
multiple RF mixers 540_1 to 540_4, multiple band-pass filters 550_1
to 550_4, multiple sigma-delta modulation circuits 560_1 to 560_4,
a DAC 570, and a parallel-to-serial converter 580. In this
embodiment, the television signal processing circuit 500 is a
single chip, and is disposed in an STB. Further, the television
signal processing circuit 500 generates a plurality of television
channel signals having predetermined frequencies through an antenna
of the STB to an external television. The plurality of television
channel signals having the predetermined frequencies may be signals
of the third and the fourth channels (with frequencies 61.25 MHz
and 67.25 MHz, respectively) defined by the NTSC, or signals of the
third and fifth channels (with frequencies 55.25 MHz and 63.25 MHz,
respectively) defined by the PAL standard.
[0019] In an operation process of the television signal processing
circuit 500, the AV signal generating circuit 510 receives a
digital video signal and a digital audio signal to generate a
digital AV signal, whose spectrum diagram may be referred from FIG.
2. The IF mixer 520 converts the digital AV signal to an IF AV
signal by using a local oscillation signal LO1, and the vestigial
sideband filter 530 filters the IF AV signal to generate a filtered
IF AV signal. FIG. 3 shows a spectrum diagram of the IF AV signal
and the frequency that the vestigial sideband filter 530 allows
passing. The interpolation circuit 534 samples and interpolates the
filtered IF AV signal to generate multiple filtered IF AV signals
to the serial-to-parallel converter 536. By increasing the number
of samples by the interpolation circuit, the probability of
interfering subsequent signals as a result of in-band quantized
noises may be reduced and the signal accuracy may be increased. The
serial-to-parallel converter 536 transmits the multiple filtered IF
AV signal having been interpolated to the multiple RF mixers 540_1
to 540_4. Each of the multiple RF mixers 540_1 to 540_4 converts
the up-converted signal received to an RF AV signal by using a
local oscillation signal LO2. Further, the band-pass filters 550_1
to 550_4 filter the RF AV signals outputted by the RF mixers 540_1
to 540_4 to generate filtered RF AV signals. FIG. 4 shows a
spectrum diagram of the RF AV signals and the frequency that the
band-pass filters 550_1 to 550_4 allow passing. In this embodiment,
there are four RF mixers that perform signal processing in a
parallel manner, and so the serial-to-parallel converter 536
transmits four filtered IF AV signals having been interpolated
respectively to the RF mixers 540_1 to 540_4, for example. One
person skilled in the art may perform signal processing in a
parallel manner by using fewer or more RF mixers based on
requirements. Next, the sigma-delta modulation circuits 560_1 to
560_4 performs a noise shifting process on the filtered RF AV
signals, respectively, to generate processed signals. The processed
signals are then processed by the parallel-to-serial converter 580,
transmitted to the DAC 570 and converted to an analog AV signal
Vout, which is then transmitted to a television via an antenna. The
parallel-to-serial converter 580 corresponds to the
serial-to-parallel converter 536. In this embodiment, the
parallel-to-serial converter 580 is coupled between the sigma-delta
modulation circuits 560_1 to 560_4 and the DAC 570. In practice,
the parallel-to-serial converter 580 may be connected between the
band-pass filter 550 and the sigma-delta modulation circuits 560_1
to 560_4, or after the DAC 570. The number of the corresponding
band-pass filters and the number of the corresponding sigma-delta
modulation circuits may be adjusted by one person skilled in the
art.
[0020] The operation concept of the television signal processing
circuit 500 in FIG. 5 is similar to that of the television signal
processing circuit 100 in FIG. 1. In the television signal
processing circuit 500, the object of adopting multiple RF mixers,
band-pass filters and sigma-delta modulation circuits is to achieve
parallel operations, so as to lower the requirement on the
operation speed for the signal processing circuit 500.
[0021] In the television signal processing system 500 in FIG. 5,
most signal processing units and all of the filtering circuits are
implemented by digital circuits, and are integrated in one single
chip, thereby significantly reducing the circuit structure and
production costs. Further, by adjusting the signal to the
intermediate frequency to perform vestigial sideband filtering, a
real filter having a simpler structure, instead of a SAW filter or
a complex filter, may be adopted in the television signal
processing circuit 500 to further lower design and production
costs. Further, by increasing the number of samples through the
interpolation circuit, the probability of interfering subsequent
signals as a result of in-band quantized noises may be reduced and
the signal accuracy may be increased. Further, the parallel
processing of the serial-to-parallel converting coordinating with
the parallel-to-serial converter overcomes the limitation of the
processing speed of the circuit.
[0022] FIG. 6 shows a flowchart of a signal processing method
according to an embodiment of the present invention. Referring to
FIG. 1 to FIG. 5 as well as the above disclosure, details of the
process of are given below.
[0023] In step 600, the process begins.
[0024] In step 602, a digital AV signal is generated.
[0025] In step 604, the digital AV signal is converted to an IF AV
signal.
[0026] In step 606, the IF AV signal is filtered to generate a
filtered IF AV signal.
[0027] In step 608, the filtered IF AV signal is converted to an RF
AV signal.
[0028] In step 610, the RF AV signal is filtered to generate a
filtered RF AV signal.
[0029] In step 612, the filtered RF AV signal is converted to an
analog AV signal and transmitted to an antenna.
[0030] In summary, in the television signal processing circuit of
the present invention, the main signal processing circuits and
filters are implemented by digital circuits, and the filters are
real filters. Therefore, the overall circuit structure does not
need to be additionally provided with more costly SAW filters or
complex filters, and significantly reduces design and production
costs.
[0031] While the invention has been described by way of example and
in terms of the preferred embodiments, it is to be understood that
the invention is not limited thereto. On the contrary, it is
intended to cover various modifications and similar arrangements
and procedures, and the scope of the appended claims therefore
should be accorded the broadest interpretation so as to encompass
all such modifications and similar arrangements and procedures.
* * * * *