JP4795716B2 - Terrestrial digital television tuner - Google Patents

Description

  The present invention relates to a terrestrial digital television tuner suitable for receiving so-called terrestrial digital broadcasting.

As shown in FIG. 4 , a part of the digital broadcast receiver uses a conventional analog-type television broadcast receiving tuner 11 as it is.

  That is, the tuner 11 has an input tuning circuit 12, a mixing circuit 13, a local oscillation circuit 14, and an output filter 15. The input tuning circuit 12 is tuned to the frequency of the signal corresponding to each channel to be received. The tuning frequency is variable so that a channel from a low frequency channel to a high frequency channel can be selected. The received signal selected by the input tuning circuit 12 is input to the mixing circuit 13 without being substantially attenuated.

  The reception signal input to the mixing circuit 13 is mixed with the local oscillation signal from the local oscillation circuit 14 to be converted into an intermediate frequency signal. The frequency of the intermediate frequency signal is the same as the intermediate frequency of an analog television. Therefore, the frequency of the local oscillation signal from the local oscillation circuit 14 is also uniquely determined, and the frequency of the local oscillation signal is always higher than the frequency of the reception signal by the frequency of the intermediate frequency signal.

  The intermediate frequency signal from the mixing circuit 13 is output via the output filter 15. The output filter 15 is composed of a band-pass filter having a pass band of approximately 6 MHz, and removes adjacent channel signals. A digital signal demodulator 16 is connected to the tuner 11 (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-304262 (FIG. 2)

  Recently, terrestrial digital broadcasting has been installed in a car for viewing, but there are cases in which a car is equipped with a GPS receiver for car navigation. In this state, when the signal of the channel 56 of the UHF band is received, the center value of the reception frequency becomes 731.143 MHz, the local oscillation frequency becomes 788.143 MHz (= 731.1143 + 57 MHz (intermediate frequency)), and the local oscillation signal Of the second harmonic (1576.6286 MHz) becomes close to the GPS signal frequency of 175.42 MHz, and this second harmonic may jump into the GPS receiver and cause reception interference.

  An object of the present invention is to provide a digital terrestrial television tuner that does not cause interference with a GPS receiver.

To solve the above problem, a first solving means includes a tuning circuit that can be tuned to a reception channel, a mixer that is provided in a subsequent stage of the tuning circuit, and that converts the frequency of the reception channel signal to an intermediate frequency signal of a predetermined frequency, and And an oscillator for supplying a local oscillation signal to the mixer, and a digital demodulator having a spectrum inverter provided at the subsequent stage of the mixer, and when receiving signals other than the channel 56 in the UHF band , the mixer uses an upper heterodyne method. The reception channel signal is frequency-converted to an intermediate frequency signal, and the digital demodulator demodulates the intermediate frequency signal. Upon reception of the channel 56 , the mixer converts the reception channel signal into an intermediate frequency signal by a lower heterodyne method. the converts digital demodulator front The spectrum of the intermediate frequency signal upside down to be demodulated by the spectrum inverter.

  In the second solution, a common control voltage for controlling the tuning frequency of the tuning circuit and the oscillation frequency of the oscillator is supplied to the tuning circuit and the oscillator, and the oscillation frequency is set to the oscillator. A resonance circuit is provided to switch the resonance frequency of the resonance circuit.

  According to a third solution, the resonance circuit includes at least an inductance element, and a varactor diode to which the control voltage is applied and connected in parallel to the inductance element, so as to switch an inductance value of the inductance element. It is configured to be small when receiving other than the channel 56, and large when receiving the channel 56.

  According to a fourth solving means, the inductance element has a first inductance element and a second inductance element connected in series with each other, and the first switch means is connected in parallel to one of the inductance elements. The first switch means is turned on when receiving other than the channel 56, and turned off when receiving the channel 56.

  According to a fifth solution, the resonance circuit includes at least an inductance element and a varactor diode to which the control voltage is applied, and the control voltage is applied to the cathode of the varactor diode via a first resistor. The cathode of the varactor diode is grounded via a series circuit of a second resistor and a second switch means, and the second switch means is turned off when receiving other than the channel 56, and when receiving the channel 56 It was turned on.

  As a sixth solution, the oscillator is supplied with a control voltage for controlling the oscillation frequency of the oscillator, and the tuning circuit is supplied with the control voltage for controlling the tuning frequency of the tuning circuit. And a voltage higher than the control voltage is supplied via the fourth resistor and the third switch means in series, and the third switch means is turned on when receiving the channel 56. did.

According to the first solution, a tuning circuit that can be tuned to a reception channel, a mixer that is provided in a subsequent stage of the tuning circuit, and that converts the frequency of the reception channel signal to an intermediate frequency signal of a predetermined frequency, and the mixer An oscillator for supplying a local oscillation signal and a digital demodulator having a spectrum inverter are provided at the subsequent stage of the mixer . When receiving signals other than the channel 56 in the UHF band , the mixer uses the upper heterodyne method to receive the reception channel signal. Is converted to an intermediate frequency signal, and the digital demodulator demodulates the intermediate frequency signal. Upon reception of the channel 56 , the mixer frequency-converts the received channel signal into an intermediate frequency signal by a lower heterodyne method. A digital demodulator is connected to the spectrum. Since demodulating the spectrum of the intermediate frequency signal by the inverter upside down to the local oscillation frequency of the channel 56 during reception becomes 674.143MHz, 2 harmonic thereof becomes 1348.286MHz. Since this frequency is far away from the frequency 1575.42 MHz of the GPS signal, even if it jumps into the GPS receiver, the GPS receiver is not subject to reception interference.

  According to the second solution, the tuning circuit and the oscillator are supplied with a common control voltage for controlling the tuning frequency of the tuning circuit and the oscillation frequency of the oscillator, and the oscillator is used for setting the oscillation frequency. Since the resonance circuit is provided and the resonance frequency of the resonance circuit is switched, the lower heterodyne method can be changed without changing the tuning voltage.

  According to the third solution, the resonance circuit includes at least an inductance element and a varactor diode to which a control voltage is applied and is connected in parallel to the inductance element, and is configured to switch an inductance value of the inductance element. However, since the frequency is reduced when receiving other than channel 56 and increased when receiving channel 56, the oscillation frequency at the time of reception of channel 56 can be set to a low frequency corresponding to the lower heterodyne system.

  According to the fourth solution means, the inductance element has a first inductance element and a second inductance element connected in series with each other, and the first switch means is connected in parallel to one inductance element. Since the first switch means is turned on when receiving other than the channel 56 and turned off when receiving the channel 56, the inductance value of the resonance circuit can be increased.

  According to the fifth solving means, the resonance circuit has at least an inductance element and a varactor diode to which a control voltage is applied, and the control voltage is applied to the cathode of the varactor diode via the first resistor, Since the cathode of the varactor diode is grounded via the series circuit of the second resistor and the second switch means, the second switch means is turned off when receiving other than the channel 56, and turned on when receiving the channel 56. In 56, the oscillation frequency at the time of reception can be set to a low frequency corresponding to the lower heterodyne system.

  According to the sixth solution, the oscillator is supplied with a control voltage for controlling the oscillation frequency of the oscillator, and the tuning circuit is supplied with the control voltage for controlling the tuning frequency of the tuning circuit by the third resistor. Since a voltage higher than the control voltage is supplied via the fourth resistor and the third switch means in series, and the third switch means is turned on when receiving the channel 56, the channel 56 is turned on. Can be converted by the lower heterodyne method.

  FIG. 1 shows the configuration of the first embodiment of the present invention. A first band-pass filter 2 is coupled to the antenna 1, and a high-frequency amplifier 3, a second band-pass filter 4, a mixer 5, an intermediate frequency amplifier 7, digital demodulation are provided on the rear side of the first band-pass filter 2. The devices 8 are sequentially connected. A local oscillation signal is supplied from the oscillator 6 to the mixer 5.

  The first band pass filter 2 is constituted by, for example, a single tuning circuit, and the tuning frequency is changed corresponding to the digital television signal of the channel to be received. The second band-pass filter 4 is composed of, for example, a double tuning circuit, and similarly, its tuning frequency is changed corresponding to the digital television signal of the channel to be received.

  In order to do so, the first bandpass filter 2 and the second bandpass filter 4 are each provided with a varactor diode (not shown), and the control voltage Vt applied to the varactor diode is changed. The control voltage Vt is supplied from the PLL circuit 9. A high voltage B for generating a control voltage Vt is applied to the PLL circuit 9 through a voltage drop resistor 10, and the high voltage B is dropped by channel selection data to generate a control voltage Vt. . The control voltage Vt corresponds to the frequency of the channel to be received.

The oscillator 6 is provided with an oscillation transistor (not shown) and a resonance circuit 6a coupled thereto. The resonance circuit 6a includes a first inductance element L1 and a second inductance element L2 connected in series with each other, a varactor diode Vd connected in parallel to the first inductance element L1, and a first inductance element connected in parallel to one inductance element L2. Switch means Sw1, and the anode of the varactor diode Vd is grounded in a DC manner. A control voltage Vt is applied to the cathode of the varactor diode Vd. The first switch means Sw1 is composed of a switch diode, for example, and is turned on or off by a control circuit (not shown).

  Although not shown, instead of connecting the first switch means Sw1 in parallel to the second inductance element L2, a capacitor element may be connected in parallel to the varactor diode Vd by the first switch means Sw1.

  In the above configuration, when receiving a channel other than the UHF band channel 56, the first switch means Sw1 is in the on state. In this state, the oscillator 6 oscillates at a frequency 57 MHz higher than the reception frequency. Therefore, the mixer 5 mixes the reception frequency, the reception frequency, and the local oscillation frequency, and outputs an intermediate frequency signal centered on 57 MHz, which is a frequency difference between them. That is, the received signal is frequency-converted by the upper heterodyne method. This intermediate frequency signal is demodulated in the digital demodulator 8.

  However, only when the terrestrial digital TV signal of the channel 56 of the UHF band is received, the first switch means Sw1 is switched to the off state. The center value of the reception frequency of the channel 56 is 731.143 MHz. Then, the inductance value of the resonance circuit 6a increases and the oscillation frequency decreases. The inductance value of the second inductance element L2 is adjusted so that the frequency is lower than the reception frequency by an intermediate frequency (57 MHz). That is, it oscillates at (731.143−57 = 674.143) MHz. This frequency corresponds to the local oscillation frequency when channel 37 is received. Even in this case, the center frequency of the intermediate frequency signal is 57 MHz. However, since the local oscillation frequency is lower than the reception frequency, the frequency is converted by the lower heterodyne system.

  Since the local oscillation frequency at the time of channel 56 reception is 674.143 MHz, its second harmonic is 1348.286 MHz, which is far away from the frequency 1575.42 MHz of the GPS signal. Even if you jump into the plane, the GPS receiver will not be disturbed.

  The frequency spectrum is reversed between the intermediate frequency signal of channel 56 and the intermediate frequency signal other than channel 56. In order to solve this problem, a digital demodulator 8 having a spectrum inverter function is used. The When receiving the terrestrial digital TV signal of channel 56, the spectrum of the intermediate frequency signal is demodulated by turning it upside down with a spectrum inverter. Usually, a spectrum inverter is added to the digital demodulator 8.

  FIG. 2 shows a second embodiment. The difference from FIG. 1 is the configuration of the resonance circuit 6a, and the other configurations are the same as those in FIG. The resonance circuit 6a includes an inductance element L and a varactor diode Vd connected in parallel thereto. The anode of the varactor diode Vd is grounded in a direct current manner. The control voltage Vt is applied to the cathode via the first resistor R1. The cathode of the varactor diode Vd is grounded via a series circuit of the second switch means Sw2 and the second resistor R2. The second switch means Sw2 is also composed of a switch diode or the like and is turned on or off by a control circuit (not shown).

  In the configuration of FIG. 2, when a channel other than the UHF band channel 56 is received, the second switch means Sw2 is in an off state. In this state, the oscillator 6 oscillates at a frequency 57 MHz higher than the reception frequency. Therefore, the mixer 5 mixes the reception frequency, the reception frequency, and the local oscillation frequency, and outputs an intermediate frequency signal centered on 57 MHz, which is a frequency difference between them. This intermediate frequency signal is demodulated in the digital demodulator 8.

  However, the second switch means Sw2 is switched to the ON state only when the terrestrial digital TV signal of the UHF band channel 56 is received. Then, since the control voltage Vt is divided by the first resistor R1 and the second resistor R2 and a low voltage is applied to the cathode of the varactor diode Vd, the capacitance value of the varactor diode Vd increases and the oscillation frequency is increased. Becomes lower. The resistance values of the first resistor R1 and the second resistor R2 are adjusted so that the frequency is lower than the reception frequency by an intermediate frequency (57 MHz). That is, the second embodiment also oscillates at (731.143−57 = 674.143) MHz.

  FIG. 3 shows a third embodiment. In FIG. 3, the control voltage is applied to the varactor diode Vd without switching the resonance frequency of the resonance circuit 6a, and the control voltage Vt is applied to the two bandpass filters 2 and 4 via the third resistor R3. At the same time, the high voltage power source B is applied via the fourth resistor R4 and the third switch means Sw3 in series.

When receiving the channel 56, the control voltage Vt is set to the value when receiving the channel 37, and the third switch means Sw3 is turned on. Then, the voltage at the connection point between the third resistor R3 and the third switch means Sw3 increases, but the third resistor R3 and the fourth switch are set so that this voltage becomes a voltage necessary for reception in the channel 56. The resistance value of the resistor R4 is set. As a result, when channel 56 is received, frequency conversion is performed by the lower heterodyne method.

  The first to third switch means Sw1 to Sw3 can be easily configured by transistors or diodes.

1 is a circuit diagram showing a configuration of a first embodiment in a terrestrial digital television tuner of the present invention. FIG. It is a circuit diagram which shows the structure of 2nd Embodiment in the terrestrial digital television tuner of this invention. The structure of 3rd Embodiment in the terrestrial digital television tuner of this invention is shown. FIG. It is a circuit diagram which shows the structure of the conventional terrestrial digital television tuner.

Explanation of symbols

1: Antenna 2: First band pass filter 3: High frequency amplifier 4: Second band pass filter 5: Mixer 6: Oscillator 6a: Resonant circuit 7: Intermediate frequency amplifier 8: Digital demodulator 9: PLL circuit 10: Voltage Drop resistance 11: High voltage power supply L: Inductance element L1: First inductance element L2: Second inductance element Vd: Varactor diode Sw1: First switch means Sw2: Second switch means Sw3: Third switch Means R1: First resistor R2: Second resistor R3: Third resistor R4: Fourth resistor

Claims (6)

A tuning circuit that can be tuned to a reception channel; a mixer that is provided at a subsequent stage of the tuning circuit and that converts the frequency of the reception channel signal into an intermediate frequency signal of a predetermined frequency; and an oscillator that supplies a local oscillation signal to the mixer ; And a digital demodulator having a spectrum inverter. The mixer converts the received channel signal into an intermediate frequency signal by an upper heterodyne system when receiving signals other than the UHF band channel 56. the demodulated digital demodulator the intermediate frequency signal, at the time of reception of the channel 56, the digital demodulator with the mixer for frequency-converting the received channel signal by the low earth heterodyne system into an intermediate frequency signal is the by the spectrum inverter Terrestrial digital television tuner characterized by demodulating the spectrum between frequency signals upside down to.   The tuning circuit and the oscillator are supplied with a common control voltage for controlling the tuning frequency of the tuning circuit and the oscillation frequency of the oscillator, and the oscillator is provided with a resonance circuit for setting the oscillation frequency, 2. The digital terrestrial television tuner according to claim 1, wherein the resonance frequency of the resonance circuit is switched.   The resonant circuit includes at least an inductance element and a varactor diode to which the control voltage is applied and connected in parallel to the inductance element, and is configured to switch an inductance value of the inductance element. 3. The terrestrial digital television tuner according to claim 2, wherein the terrestrial digital television tuner is reduced when receiving and is increased when receiving the channel 56.   The inductance element has a first inductance element and a second inductance element connected in series to each other, and a first switch means is connected in parallel to one of the inductance elements, and the first switch means is 4. The digital terrestrial television tuner according to claim 3, wherein the digital terrestrial television tuner is turned on when receiving other than channel 56 and turned off when receiving channel 56.   The resonant circuit includes at least an inductance element and a varactor diode to which the control voltage is applied. The control voltage is applied to the cathode of the varactor diode via a first resistor, and the cathode of the varactor diode is connected to the cathode of the varactor diode. The second switch means is turned off when receiving other than the channel 56 and turned on when receiving the channel 56, and is grounded via a series circuit of two resistors and second switch means. Item 3. The terrestrial digital television tuner according to Item 2. The oscillator is supplied with a control voltage for controlling the oscillation frequency of the oscillator, and the tuning circuit is supplied with the control voltage for controlling the tuning frequency of the tuning circuit via a third resistor. , a voltage higher than the control voltage supply through a fourth resistor and a third switch means in series, 請you featuring that it has to turn on the third switch means upon receipt of the channel 56 determined Item 2. The terrestrial digital television tuner according to Item 1.

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