Pulse or digital communications – Apparatus convertible to analog
Reexamination Certificate
2000-09-19
2004-11-02
Tse, Young T. (Department: 2637)
Pulse or digital communications
Apparatus convertible to analog
C375S344000, C375S324000, C375S329000, C370S478000, C329S306000
Reexamination Certificate
active
06813310
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a receiver capable of receiving an analog broadcast and a digital broadcast and an integrated circuit (IC) for the same.
2. Description of Related Art
In the current amplitude modulation (AM) broadcast and the current frequency modulation (FM) broadcast, the processing of materials to be broadcast is being digitized. However, the broadcasts themselves are performed in an analog system.
However, if the broadcasts themselves are digitized, a broadcast in high sound quality can be supplied, and additional data service and the like can be enabled, and further the efficiency of frequency utilization can be improved. Accordingly, a digital broadcast, in which broadcast themselves are digitized, is now under consideration.
However, it is a matter of course that a digital broadcast receiver is newly required in place of a conventional analog broadcast receiver for receiving the digital broadcast. On the other hand, it is desirable to change over from the analog broadcast to the digital broadcast smoothly without any resistance. Consequently, the coexistence of the former analog broadcast and the new digital broadcast is required during the period of the changeover.
There is the IBOC (In-Band On Channel) system as a broadcast system enabling the coexistence. The IBOC system realizes the coexistence by employing a frequency disposition of the analog broadcast and the digital broadcast as shown in
FIG. 4A
, for example.
That is, in
FIG. 4A
, a reference code S
A
indicates a broadcast wave signal of a conventional analog FM broadcast, or an FM signal. The carrier frequency of the broadcast wave signal S
A
is a frequency f
RX
. In a case of making a digital broadcast wave signal coexist with the analog broadcast wave signal S
A
, two digital broadcast wave signals S
D
are disposed adjacently to the both side frequency bands of the broadcast wave signal S
A
.
However, there is a case where only one of the two digital broadcast wave signals S
D
is used. In addition, the levels of the digital broadcast wave signals S
D
are set to be lower than that of the analog broadcast wave signal S
A
by about 15 dB-20 dB. The program contents of the digital broadcast wave signals SD are generally the same as those of the analog broadcast wave signal S
A
.
In future, the analog broadcast wave signal S
A
will be stopped from being broadcast, and only the digital broadcast wave signal S
D
will be broadcast. Or, the frequency band of the analog broadcast wave signal S
A
will be used by the digital broadcast. Incidentally, it is regarded that it will take from ten years to fifteen years to change over from the analog broadcast to the digital broadcast.
For coping with the aforesaid coexistence of the analog broadcast and the digital broadcast, a receiver that can be used during the changeover period and after it, namely, a hybrid receiver that can receive both of the analog broadcast and the digital broadcast, is required.
The hybrid receiver can be constructed as shown in
FIG. 5
, for example. For simplifying the situation, it is supposed that the analog broadcast wave signal S
A
and both the digital broadcast wave signals S
D
are broadcast as shown in FIG.
4
A. The antenna
1
receives these signals S
A
and S
D
. Then, the received signals S
A
and S
D
are supplied to a mixer circuit
5
though a signal line composed of an antenna tuning circuit
2
, a high frequency amplifier
3
and an interstage tuning circuit
4
in the order. On the other hand, a local oscillation circuit
6
forms a local oscillation signal S
LO
having a predetermined frequency, and the formed local oscillation signal S
LO
is also supplied to the mixer circuit
5
.
Thus, the frequency conversion of the received signals S
A
and S
D
are performed in the mixer circuit
5
by means of the local oscillation signal S
LO
. As a result of the frequency conversion, as shown in
FIG. 4B
, the received signals S
A
and S
D
are converted to intermediate-frequency signals S
AI
and S
DI
in which the carrier frequency f
RX
of the signal S
A
becomes a predetermined intermediate frequency f
IF
. The converted intermediate-frequency signals S
AI
and S
DI
are then supplied to a band-pass filter
7
. The band-pass filter
7
works as an intermediate-frequency filter and has a wide frequency band passing characteristic as shown by a dashed line
7
F in FIG.
4
B. Then an output of the band-pass filter
7
is supplied to a band-pass filter
9
A and a band-elimination filter
9
D through an AGC amplifier
8
.
In this case, the band-pass filter
9
A is used for eliminating an adjacent disturbance wave signal, and has a center frequency of a frequency f
IF
and a pass band corresponding to the intermediate-frequency signal S
AI
, as shown by a dashed line
9
AF in FIG.
4
C. Consequently, the intermediate-frequency signal S
AI
Of the analog broadcast is taken out of the band-pass filter
9
A.
Besides, the band-elimination filter
9
D is used for attenuating the analog intermediate-frequency signal S
AI
, and has a center frequency of a frequency f
IF
and an elimination band same as the frequency band of the intermediate-frequency signal S
AI
, as shown by dashed lines
9
DF in FIG.
4
D. Consequently, the intermediate-frequency signals S
DI
of the digital broadcast are taken out of the band-elimination filter
9
D.
Accordingly, when only the analog broadcast is broadcast or when both of the analog broadcast and the digital broadcast are broadcast, the analog broadcast can be heard by demodulating the intermediate-frequency signal S
AI
outputted from the band-pass filter
9
A.
On the other hand, when only the digital broadcast is broadcast or when both of the analog broadcast and the digital broadcast are broadcast, the digital broadcast can be heard by decoding the intermediate-frequency signals S
DI
outputted from the band-elimination filter
9
D.
Consequently, any one of the analog broadcast and the digital broadcast in conformity with the IBOC system can be heard by means of the receiver shown in FIG.
5
. Furthermore, the receiver can be used as it is even if only the digital broadcast is broadcast in future.
However, the pass band width of the band-pass filter
7
should be wide for taking out the two kinds of the intermediate-frequency signals S
AI
and S
DI
. On the other hand, the band-pass filter
7
should eliminate disturbance wave signals from adjacent channels. As a result, the ratio band, i.e. a ratio of a cutoff frequency band to a pass frequency band, becomes small. Consequently, the requirements for the band-pass filter
7
become strict. As a result, the order and/or the scale of the band-pass filter
7
becomes large.
Furthermore, because the band-pass filter
9
A and the band-elimination filter
9
D are required in addition to the band-pass filter
7
, many filters become necessary. Consequently, the increase of consumption current owing to the increase of the circuit scale, the increase of the size of a receiver, the increase of costs, and the like are incurred.
SUMMARY OF THE INVENTION
The present invention aims to solve the aforesaid problems. That is, the present invention aims to provide a receiver and an IC that can receive the analog broadcast and the digital broadcast, and that can make the ratio of the band-pass filter for taking out an object intermediate-frequency signal not to be small for preventing the order and scale of the bandpass filter from increasing, and further that can prevent the increase of the circuit scale, the increase of the size of a receiver, the increase of costs, and the like.
According to a first aspect of the present invention, there is provided a receiver for a broadcast system in which a broadcast wave signal of an analog broadcast and a broadcast wave signal of a digital broadcast are transmitted in frequency bands adjacent to each other, comprising: mixer means, to which a received signal and a local oscillation signal are supplied, and which performs a frequency conversion of the re
Chang Edith
Maioli Jay H.
Sony Corporation
Tse Young T.
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