Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Reexamination Certificate
1998-12-09
2002-01-29
Kincaid, Lester G. (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
C455S300000, C455S553100, C348S731000
Reexamination Certificate
active
06343209
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a tuner for digital and analog use, for selectively receiving digital modulated television signals and analog modulated television signals.
BACKGROUND OF THE INVENTION
Recently, with the shift to digital television broadcasting, development of television receivers capable of receiving both analog and digital broadcasts has been pursued. In the United States, and other industrial nations, the digital modulation method which has been adopted for terrestrial broadcast television is 8VSB (8 Vestigial Sideband). Since 8VSB uses the same CH (channel) bandwidth as conventional analog broadcasting (NTSC: National Television System Committee), the conventional front end can be used in almost unchanged form.
FIG. 9
shows one example of a front-end system (from front end to demodulation circuits) which uses the double-conversion method, including a conventional tuner for digital and analog use. This conventional front-end system is made up of a frequency conversion section
100
, a switch section
101
, a down-converter section
102
, an A/D conversion section
103
, a VSB demodulation section
104
, and an NTSC demodulation section
105
. Further, in this conventional example, members from a signal input terminal
115
, through the frequency conversion section
100
, up to an IF (Intermediate Frequency) signal output terminal
130
are collectively referred to as a “tuner for digital and analog use.”
The frequency conversion section
100
can be further divided into first and second conversion sections
106
and
107
. The first conversion section
106
is made up of an RF amplifier
108
, a first mixer
109
, a BPF (Band-Pass Filter)
110
, a first IF amplifier
111
, a BPF
112
, a first local oscillator
113
, and a first PLL (Phase Locked Loop) circuit
114
. Further, the first local oscillator
113
and the first PLL circuit
114
form a closed loop.
An input signal from the signal input terminal
115
first undergoes wideband amplification by the RF amplifier
108
. Meanwhile, first PLL control data
116
is applied, via a terminal
117
, to the first PLL circuit
114
, and, by means of a signal from the first PLL circuit
114
, the first local oscillator
113
produces a first local signal of a frequency specified by the first PLL control data
116
. Then, in the first mixer
109
, the output from the RF amplifier
108
and the first local signal produced by the first PLL circuit
114
and the first local oscillator
113
are mixed and up-converted into a first IF signal. The first IF signal, after undergoing band limiting in the BPF
110
, is amplified by the first IF amplifier
111
, and is then band limited by the BPF
112
and outputted to the second conversion section
107
.
The second conversion section
107
is made up of a second mixer
118
, a second IF amplifier
119
, a BPF
120
, a second local oscillator
121
, and a second PLL circuit
122
. Further, the second local oscillator
121
and the second PLL circuit
122
form a closed loop.
Second PLL control data
123
is applied, via a terminal
124
, to the second PLL circuit
122
, and, by means of a signal from the second PLL circuit
122
, the second local oscillator
121
produces a second local signal of a frequency specified by the second PLL control data
123
. Then, in the second mixer
118
, the output from the BPF
112
of the first conversion section
106
and the second local signal produced by the second PLL circuit
122
and the second local oscillator
121
are mixed and down-converted into a second IF signal. The second IF signal is amplified by the second IF amplifier
119
, and is then band limited by the BPF
120
and outputted to the IF signal output terminal
130
.
The switch section
101
, based on an external control signal
125
in accordance with the type of received signal (analog/digital), switches the destination to which to send the second IF signal from the IF signal output terminal
130
. By means of the switching of the switch section
101
, a second IF signal corresponding to a digital broadcast signal is sent, via a terminal
141
, to the down-converter section
102
. A second IF signal corresponding to an analog broadcast signal, on the other hand, is sent, via a terminal
142
, directly to the NTSC demodulation section
105
.
The down-converter section
102
is a signal conversion means which converts the second IF signal obtained via the switch section
101
(hereinafter referred to simply as the “IF signal”) to a signal suitable for input to a digital processing system. The down-converter section
102
is made up of a BPF
126
, a digital IF amplifier
127
, a down-converter mixer
128
, and a down-converter local oscillator
129
.
An IF signal corresponding to a digital broadcast signal, obtained through the switch section
101
, undergoes band limiting necessary for digital demodulation, in the BPF
126
, and is then amplified by the digital IF amplifier
127
. In the down-converter mixer
128
, the IF signal from the digital IF amplifier
127
and a signal produced by the down-converter local oscillator
129
are mixed and down-converted. The down-converted IF signal is then outputted, as a Low IF signal, to the A/D conversion section
103
.
The A/D conversion section
103
converts the Low IF signal from the down-converter section
102
into a digital signal. The VSB (Vestigial Sideband) demodulation section
104
performs VSB demodulation of the digital signal from the A/D conversion section
103
, and outputs a transport stream signal.
The NTSC demodulation section
105
, on the other hand, performs NTSC demodulation of an IF signal corresponding to an analog broadcast signal, obtained through the switch section
101
.
However, in the foregoing conventional front-end system, the frequency conversion section
100
, the signal input terminal
115
, and the IF signal output terminal
130
were contained, as a tuner for digital and analog use, in a single body
131
, and the other circuits (the down-converter section
102
, the A/D conversion section
103
, the VSB demodulation section
104
, and the NTSC demodulation section
105
) were provided together on a common board.
Further, in the foregoing front-end system with conventional tuner for digital and analog use, a single control signal
125
was used to control the operations of the switch section
101
, the down-converter section
102
, the A/D conversion section
103
, the VSB demodulation section
104
, and the NTSC demodulation section
105
.
Accordingly, with the foregoing conventional art, when receiving a digital broadcast signal, the down-converter section
102
was susceptible to the influence of noise produced by the digital processing system following the A/D conversion section
103
. This caused impairment of characteristics of the down-converter local oscillator
129
of the down-converter section
102
, such as precision of the local oscillating frequency. Further, since the down-converter section
102
was not enclosed by a body, there were problems with unnecessary radiation produced thereby.
Moreover, the foregoing problems also arose in a conventional front-end system for digital and analog use in which a baseband demodulation section was provided as the foregoing signal conversion means. The following will explain this conventional front-end system. Here, members having the same structure and functions as those explained above will be given the same reference numbers, and explanation thereof will be omitted here.
As shown in
FIG. 10
, this conventional front-end system, which uses the double conversion method, is made up of a frequency conversion section
100
, a switch section
101
, a baseband demodulation section
150
, an A/D conversion section
103
, a VSB demodulation section
104
, and an NTSC demodulation section
105
. Here again, a signal input terminal
115
, the frequency conversion section
100
, and an IF signal output terminal
130
are collectively referred to as a “tuner for digital and analog use.”
The switch section
101
, based
Maeda Tatsuo
Masuda Shigeto
Kincaid Lester G.
Sharp Kabushiki Kaisha
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