Television – Receiver circuitry – Television receiver adapted to receive radio broadcast or in...
Reexamination Certificate
2001-03-21
2004-05-04
Miller, John (Department: 2614)
Television
Receiver circuitry
Television receiver adapted to receive radio broadcast or in...
C348S731000, C348S737000, C375S345000, C455S179100
Reexamination Certificate
active
06731348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a television tuner capable of receiving FM broadcast signals.
2. Description of the Related Art
FIG. 5
illustrates a television tuner capable of receiving FM broadcast signals. A television signal, represented by TV, or an FM broadcast signal, represented by FM, is received by an input tuner circuit
21
. The input signal is conditioned by a first mixer circuit
24
, a radio frequency (RF) amplifier circuit
22
, and an interstage tuner circuit
23
.
The first mixer circuit
24
receives a local oscillation signal from a first local oscillator circuit
25
. The tuned frequency of the input tuner circuit
21
, the interstage tuner circuit
23
, and the frequency (local oscillating frequency) of the first local oscillator circuit
25
are controlled by a channel select signal S received by a phase-locked loop (PLL) circuit
26
. Generally, the local oscillating frequency is higher than the tuned frequency.
When receiving a television signal, a television intermediate-frequency signal having a video intermediate-frequency, according to US standards, e.g., a video intermediate-frequency of 45.75 MHz, is generated by the first mixer circuit
24
. When necessary, an FM broadcast signal (hereinafter referred to as the “first FM IF signal”) is converted to a television intermediate-frequency signal by the first mixer circuit
24
. The television intermediate-frequency signal generated by the first mixer circuit
24
is passed to a subsequent intermediate-frequency circuit (not shown) through a first intermediate-frequency filter
27
for further processing.
The first FM IF signal generated by the first mixer circuit
24
is also received by a second mixer circuit
29
through a second intermediate-frequency filter
28
. The second mixer circuit
29
receives a local oscillation signal from a second local oscillator circuit
30
. The frequency of the local oscillation signal generated by the second local oscillator circuit
30
is 10.7 MHz higher in frequency than the frequency of the first FM IF signal. Therefore, an FM broadcast signal (hereinafter referred to as the “second FM IF signal”) having a frequency converted to a 10.7 MHz signal is generated by the second mixer circuit
29
. The second FM IF signal is received by a demodulator circuit (not shown) through a third intermediate-frequency filter
31
.
Accordingly, a television tuner can include two mixer circuits
24
and
29
, and two local oscillator circuits
25
and
30
that achieve a two-stage frequency conversion in which an FM broadcast signal is first frequency-converted to a television intermediate-frequency signal before being converted to an intermediate-frequency signal of 10.7 MHz used in a conventional FM receiver. This two-stage structure creates beat disturbances between the two local oscillation signals, which interferes with reception.
SUMMARY OF THE INVENTION
A television tuner preferably includes a single mixer circuit and a single local oscillator circuit which provides a simplified layout that is immune to a wide range of interference such as beat disturbances.
In one aspect, a television tuner includes a mixer coupled to a local oscillator circuit. Preferably, the mixer is configured to receive a television signal and an FM broadcast signal. The local oscillator circuit generates a local oscillation signal received by the mixer circuit. When a television signal is received, a television intermediate-frequency signal is generated by the mixer circuit. When an FM broadcast signal is received, an FM intermediate-frequency signal converted to 10.7 MHz is generated by the mixer circuit. Only a single local oscillator circuit is used to obtain a television intermediate-frequency signal and an FM intermediate-frequency signal converted to about 10.7 MHz.
Preferably, the television signal or the FM broadcast signal is received by a tuner circuit that includes a mixer circuit. The local oscillation frequency and the tuned frequency of the tuner circuit can be adjusted when the local oscillation frequency is higher than the tuned frequency of the tuner circuit by a frequency of a television intermediate-frequency signal. In embodiments where the frequency of the local oscillation signal is about 10.7 MHz higher than the frequency of the FM broadcast signal, the tuned frequency may be adjusted so that the difference between the tuned frequency and the frequency of the local oscillation signal is about 10.7 MHz. Therefore, when the television signal is received, a television intermediate-frequency signal is generated by the mixer circuit, and when the FM broadcast signal is received, an FM intermediate-frequency signal having a frequency converted to about 10.7 MHz is generated by the mixer circuit.
In another aspect, the television tuner includes a first varactor diode and the local oscillator circuit includes a second varactor diode. Preferably, the frequency of the local oscillation signal is higher than the tuned frequency of the tuner circuit by a frequency of the television intermediate-frequency signal when a common voltage is applied to the first varactor diode and to the second varactor diode. In applications where the frequency of the local oscillation signal is about 10.7 MHz higher than the frequency of the FM broadcast signal, a higher voltage is applied to the first varactor diode than to the second varactor diode. The difference between the tuned frequency and the frequency of the local oscillation signal may thus be about 10.7 MHz.
The television tuner may include a phase lock loop (PLL) circuit for generating a tuning voltage that is applied to the first varactor diode and to the second varactor diode. The television tuner further includes a voltage adder circuit, and a voltage supply that supplies a positive voltage. Preferably, the tuning voltage is applied to a cathode of the second varactor diode and to an input of the voltage adder circuit. Preferably, a positive voltage is applied to the voltage adder circuit only when an FM broadcast signal is received. The positive voltage is added to the tuning voltage to generate a voltage that is applied to the cathode of the first varactor diode.
Alternatively, the television tuner may include a PLL circuit for generating a tuning voltage that is applied to the first varactor diode and to the second varactor diode and a voltage supply that supplies a negative voltage. Preferably, the tuning voltage is applied to the cathode of the first varactor diode and to the cathode of the second varactor diode, and the negative voltage is applied to an anode of the first varactor diode only when the FM broadcast signal is received. Accordingly, a higher voltage is applied to the first varactor diode.
Preferably, the television signal or the FM broadcast signal is received by a tuner circuit before the signal is conditioned by the mixer circuit. Preferably, the frequency of the local oscillation signal and the tuned frequency of the tuner circuit can be adjusted while the frequency of the local oscillation signal is higher than the tuned frequency of the tuner circuit by a frequency of the television intermediate-frequency signal. In applications where the tuned frequency corresponds to the frequency of the FM broadcast signal, the frequency of the local oscillation signal is adjusted so that the difference between the tuned frequency and the frequency of the local oscillation signal is about 10.7 MHz. Therefore, when the television signal is received, a television intermediate-frequency signal is generated by the mixer circuit. When the FM broadcast signal is received, an FM intermediate-frequency signal having a frequency converted to about 10.7 MHz is generated by the mixer circuit.
Preferably, the television tuner includes a first varactor diode and the local oscillator circuit includes a second varactor diode. Preferably, the frequency of the local oscillation signal is higher than the tuned frequency by the frequency of the television intermediate-frequency signal while a c
Furuta Toshiro
Osada Shigeru
Yamamoto Masaki
Alps Electric Co. ,Ltd.
Miller John
Yenke Brian
LandOfFree
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