Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Reexamination Certificate
1998-09-25
2001-06-05
Maung, Nay (Department: 2681)
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
C455S180200, C348S731000
Reexamination Certificate
active
06243567
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a television tuner switching a mode between UHF and VHF modes to thereby receive signals having frequencies of UHF and VHF bands, a tuner integrated circuit (IC) for controlling operation modes of such a television tuner, and a method of controlling a television tuner.
2. Description of the Related Art
In general, three frequency bands are now utilized as radio wave for television broadcasting: Very High Frequency-Low (VHF-L) band; Very High Frequency-High (VHF-H) band; and Ultra High Frequency (UHF) band.
A so-called television tuner has conventionally selected a channel by means of a logical channel (LC) tuning circuit. However, it is quite difficult to cover the above-mentioned three bands by a single LC tuning circuit. Hence, a conventional television tuner has been designed to include three LC tuning circuits each associated with the above-mentioned three bands, which LC tuning circuits are alternately switched. This is the same in a LC oscillation circuit of a frequency converter.
In the United States, a frequency band for FM radio broadcasting is positioned between VHF-L and VHF-H bands for television broadcasting. Hence, when radio waves for television broadcasting in VHF-L and VHF-H bands are to be received, radio waves for radio broadcasting in FM band may interfere with them to thereby degrade images and/or sound in quality. In order to avoid such interference, it would be necessary to trap radio waves for radio broadcasting in FM band.
In cable television service now spreading in the United States, a frequency band of signals for cable television is almost the same as a frequency band of signals for radio wave for television broadcasting, but is assigned FM band used for radio broadcasting. Hence, when a cable television is in operation, it is impossible to trap FM band.
Hence, in a television tuner available in the United States, a FM trap circuit for trapping signals of FM band is connected to an antenna through which radio waves for television broadcasting are received. The FM trap circuit is operated when radio waves for television broadcasting in VHF-L and VHF-H bands are to be received, and is paused when signals of a cable television are to be received through a cable.
A television tuner now available is not designed to switch only a LC tuning circuit in order to switch signals to be received between VHF-L and VHF-H bands, and UHF band. Circuits for amplifying high frequency and circuits for converting frequency separately prepared for VHF-L and VHF-H bands, and UHF band are connected to a front stage of a LC tuning circuit to thereby define a circuit for receiving signals having a frequency of VHF-L and VHF-H bands, and a circuit for receiving signals having a frequency of UHF band. The thus defined circuits are wholly, selectively switched.
The television tuner having such a structure as mentioned above makes it possible to simplify a circuit structure thereof, suppress degradation in characteristics, and optimize noise figure (NF) and operation current of transistors constituting the circuit, in accordance with a band. The above-mentioned control for switching circuits for receiving signals having frequencies of VHF-L and -H bands, and UHF band is generally carried out by means of operation switching signals standardized by a micro-computer, using an integrated injection logic (IIL) gate as standard specification.
An example of conventional television tuners is explained hereinbelow with reference to
FIGS. 1
,
2
A and
2
B, wherein
FIG. 1
is a block diagram of a television tuner,
FIG. 2A
is a partial block diagram of a tuner integrated circuit, and
FIG. 2B
illustrates data for switching a band.
As illustrated in
FIG. 1
, the illustrated television tuner
1
is comprised of a high frequency amplifying section
100
, a tuner integrated circuit
200
, a logical channel (LC) section
300
, and a control circuit
400
.
The high frequency amplifying section
100
amplifies signals for radio wave or cable television broadcasting. The tuner IC
200
converts the amplified television signals into an intermediate frequency. The control circuit
400
is comprised of a microcomputer in which a suitable control program is installed as software, and controls operation of the high frequency amplifying section
100
and the tuner IC
200
.
The tuner IC
200
includes a frequency converter
2
to which a tuner controller
3
is connected. The high frequency amplifying section
100
includes a first amplifier
4
for amplifying a frequency of UHF band, and a second amplifier
5
for amplifying frequencies of VHF-L and -H bands. The first and second amplifiers
4
and
5
are connected upstream to the frequency converter
2
. A FM trap circuit
6
is connected upstream to the second amplifier
5
.
The FM trap circuit
6
to which the second amplifier
5
is connected, and the first amplifier
4
are both connected to a switch device
7
, to which an antenna (not illustrated) for receiving radio wave broadcasting or a communication cable (not illustrated) for cable broadcasting is connected through an input terminal
8
.
The frequency converter
2
includes a first frequency mixer
11
for UHF band and a second frequency mixer
12
for VHF-L and -H bands, which are connected to a first local oscillator (LO)
13
for UHF band and a second local oscillator (LO)
14
for VHF-L and -H bands, respectively.
The first and second local oscillators
13
and
14
are connected to a phase locked loop (PLL) section
15
through a buffer amplifier
19
. The phase locked loop section
15
is connected to the first and second local oscillators
13
and
14
for feedback through logical channels
16
and
17
for UHF band, and VHF-L and -H bands, respectively, in the logical channel section
300
.
As mentioned above, the first and second amplifiers
4
and
5
, the first and second mixers
11
and
12
, the first and second local oscillators
13
and
14
, and the first and second logical channels
16
and
17
are equipped separately for UHF band, and VHF-L and -H bands, and are connected in series to thereby define a first circuit
500
for receiving signals having a frequency of UHF band, and a second circuit
600
for receiving signals having a frequency of VHF-L and -H bands.
The first and second local oscillators
13
and
14
oscillate at certain frequencies. The first and second mixers
11
and
12
convert frequencies of television signals in UHF band and VHF-L and -H bands into intermediate frequencies by mixing them with frequencies of oscillation made by the first and second local oscillators
13
and
14
. The phase locked loop section
15
outputs a control voltage to the first and second logical channels
16
and
17
in accordance with the oscillation frequencies of the first and second local oscillators
13
and
14
, respectively, and cooperates with the first and second logical channels
16
and
17
to control oscillation frequencies of the first and second local oscillators
13
and
14
by feed-back.
As illustrated in
FIG. 1
, the phase locked loop section
15
is comprised of a frequency divider
41
, a phase detector
42
, a standard oscillator
43
, a charge pump
44
, and a buffer amplifier
45
. The frequency divider
41
divides a local oscillation signal transmitted from the buffer amplifier
19
. The standard oscillator
43
transmits an oscillation signal having a certain frequency.
The phase detector
42
generates a voltage proportional to a difference in phase between a frequency division signal transmitted by the frequency divider
41
and the oscillation signal transmitted from the standard oscillator
43
.
The charge pump
44
increases an output voltage of the phase detector
42
up to a certain voltage. The buffer amplifier
45
removes high frequency parts out of the thus increased voltage, and outputs the resultant voltage to the first and second logical channels
16
and
17
as a control voltage.
The frequency divider
41
can vary a division ratio in accordan
Maung Nay
McGinn & Gibb PLLC
NEC Corporation
Vuong Quochien
LandOfFree
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