JPH0563131U - Satellite broadcasting tuner - Google Patents

Abstract

(57) [Summary] [Structure] Tuning circuit 3, local oscillator 4, mixer 5
, A BPF 6, a VCO 14, a phase comparator 9, a DC amplifier 10 and an AFC circuit 12, and the tuning circuit 3
However, in the satellite broadcast receiving tuner that controls the oscillation frequency of the local oscillation signal so that the AFC voltage becomes a voltage corresponding to the regular frequency of the intermediate frequency signal, the temperature characteristic of the VCO 14 becomes substantially equal to the temperature characteristic of the BPF 6. To set. [Effect] Even if the C / N ratio deteriorates during reception, the performance of the entire apparatus does not deteriorate. Further, the capture range of the PLL demodulation circuit can be minimized, and the S / N ratio is improved.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a satellite broadcast receiving tuner for converting a high frequency signal output from a BS converter into an intermediate frequency signal in a television receiver or the like for receiving satellite broadcasts.

[0002]

[Prior Art]

 FIG. 3 is a block diagram showing a configuration example of a conventional satellite broadcast receiving tuner. In this figure, 1 is an input terminal to which a high frequency signal output from a BS converter (not shown) is input, and 2 is an amplifier for amplifying the high frequency signal. High-frequency amplifier 3 is a tuning circuit that outputs a tuning voltage according to the channel selected by the viewer, 4 is a local oscillator that outputs a local oscillation signal whose oscillation frequency is controlled by the tuning voltage, and 5 is a high frequency A mixer that mixes the output signal of the amplifier 2 with a local oscillation signal to convert it to an intermediate frequency signal, and 6 is a bandpass filter (hereinafter referred to as BPF) such as a SAW (surface acoustic wave) device that passes the intermediate frequency signal. is there.

Reference numeral 7 is a PLL demodulation circuit for demodulating a composite video signal from the intermediate frequency signal. In the PLL demodulation circuit 7, 8 is a voltage controlled oscillator (hereinafter referred to as VCO) that outputs an oscillation signal of a predetermined frequency, and 9 is a phase comparison signal that compares the phase of the intermediate frequency signal with the phase of the oscillation signal. Is a DC amplifier that amplifies the phase comparison signal. The output signal of the DC amplifier 10 is output from the PLL demodulation circuit 7 as a demodulation signal, that is, a composite video signal, and the VCO 8 is controlled. It is input to the voltage input terminal. This controls the frequency of the oscillation signal.

Further, 11 is an output terminal for outputting a composite video signal, and 12 is an AFC circuit for detecting an average DC voltage of the composite video signal and outputting an AFC (automatic frequency control) voltage. 3 inputs the AFC voltage and changes the oscillation frequency of the local oscillation signal so that the AFC voltage becomes a regular voltage, that is, a voltage corresponding to the regular intermediate frequency (402.78 MHz) of the intermediate frequency signal. Control.

[0005]

[Problems to be solved by the device]

 By the way, in the satellite broadcast receiving tuner, even if the reception environment is bad, it is necessary to input the intermediate frequency signal to the PLL demodulation circuit 7 without loss, and the PLL demodulation circuit 7 is always input. It should have the best characteristics for the intermediate frequency signal.

However, since the SAW device used for the BPF 6, for example, lithium niobate (L _i N _b O ₃ ) has a temperature characteristic of about 84 ppm / ° C, the center frequency of the BPF 6 is As shown in FIG. 4, when the ambient temperature rises from room temperature, the frequency f _{0 is} decreased by Δf. Therefore, even if the output signal of the high frequency amplifier 2 is converted into the intermediate frequency signal of the regular frequency in the mixer 5, when the converted intermediate frequency signal passes through the BPF 6, the energy component at the channel end on the high frequency side is obtained. There was a problem that was missing. As a result, if the reception environment is poor and the C / N ratio deteriorates, the performance of the entire device deteriorates.

Further, in order for the PLL demodulation circuit 7 to have the best characteristics with respect to the input intermediate frequency signal at all times, the intermediate frequency signal component must be within the capture range of the PLL demodulation circuit 7. However, the capture range of the PLL demodulation circuit 7 also has temperature characteristics as shown by the shaded area in FIG. The temperature characteristic of the capture range is mainly due to the temperature characteristic of the VCO 8 shown by the straight line a in FIG. Therefore, when the ambient temperature changes, there is a problem that the intermediate frequency signal component deviates from the capture range of the PLL demodulation circuit 7. Therefore, it is necessary to widen the capture range of the PLL demodulation circuit 7, resulting in a problem that the S / N ratio is lowered.

The present invention has been made under such a background, and even if the C / N ratio is deteriorated at the time of reception, the performance of the entire device is not deteriorated, and the cap challenge of the PLL demodulation circuit is prevented. It is an object of the present invention to provide a satellite broadcast reception tuner that can be minimized and that can improve the S / N ratio.

[0009]

[Means for Solving the Problems]

 This invention is directed to a tuning circuit that outputs a tuning voltage according to a channel selected by a viewer, a local oscillator that outputs a local oscillation signal whose oscillation frequency is controlled by the tuning voltage, and a high-frequency signal. A mixer that mixes the local oscillation signal with the local oscillation signal to convert it to an intermediate frequency signal, a bandpass filter that passes the intermediate frequency signal, a voltage controlled oscillator that outputs an oscillation signal of a predetermined frequency, and the intermediate frequency signal. A phase comparator that compares the phase of the signal with the phase of the oscillation signal and outputs a phase comparison signal; and a direct current amplifier that amplifies the phase comparison signal and controls the frequency of the oscillation signal by the output signal. An AFC circuit for detecting an average DC voltage of the output signal of the DC amplifier and outputting an AFC voltage, wherein the tuning circuit is configured so that the AFC voltage is a normal frequency of the intermediate frequency signal. In the satellite broadcast receiving tuner that controls the oscillation frequency of the local oscillation signal so that the voltage corresponds to the number of the local oscillation signals, the temperature characteristic of the voltage controlled oscillator is set to be substantially equal to the temperature characteristic of the bandpass filter. The feature is to do.

[0010]

[Action]

 According to the above configuration, for example, even if the ambient temperature rises and the center frequency of the bandpass filter decreases, the temperature characteristic of the voltage controlled oscillator is almost equal to the temperature characteristic of the bandpass filter. The center frequency of is also almost the same as the center frequency of the bandpass filter, and the center frequency of the intermediate frequency signal converted in the mixer does not deviate from the center frequency of the bandpass filter.

[0011]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a satellite broadcast receiving tuner according to an embodiment of this idea. In this figure, parts corresponding to those in FIG. I will omit it. In the satellite broadcast receiving tuner shown in this figure, a PLL demodulation circuit 13 is newly provided in place of the PLL demodulation circuit 7. This PLL demodulation circuit 13 is newly provided with a VCO 14 having a temperature characteristic (see the straight line a in FIG. 2) substantially equal to the temperature characteristic of the BPF 6 shown in the broken line b in FIG. 2 instead of the VCO 8 in FIG. .. The temperature characteristic of the VCO 14 is, for example, the temperature characteristic of a capacitor used in a resonance circuit or the temperature characteristic of a forward voltage of a semiconductor element such as a diode inserted in a DC bias circuit. The temperature characteristics are almost the same as the temperature characteristics. As a result, the temperature characteristic of the capture range of the PLL demodulation circuit 13 becomes as shown by the shaded area in FIG.

In such a configuration, for example, even if the ambient temperature of the satellite broadcast receiving tuner rises and the center frequency of the BPF 6 decreases by Δf as shown in FIG. 4, the temperature characteristic of the VCO 14 still has the BPF 6 temperature characteristic. Since the center frequency of the oscillation signal of the VCO 14 is lowered by about Δf, the center frequency of the intermediate frequency signal converted by the mixer 5 does not deviate from the center frequency of the BPF 6. Therefore, even if the intermediate frequency signal passes through the BPF 6, the energy component at the channel end of the high band or the low band is not lost. As a result, even if the C / N ratio deteriorates during reception, the performance of the entire device does not deteriorate.

Further, the center frequency of the intermediate frequency signal converted in the mixer 5 matches the center frequency of the capture range of the PLL demodulation circuit 13. Therefore, the capture range of the PLL demodulation circuit 13 can be minimized, and the S / N ratio can be improved.

[0014]

As described above, according to the present invention, the center frequency of the intermediate frequency signal does not deviate from the center frequency of the bandpass filter even when the C / N ratio deteriorates during reception. The effect is that the overall performance does not deteriorate. Moreover, since the center frequency of the intermediate frequency signal becomes the center frequency of the capture range of the PLL demodulation circuit, there is an effect that the capture range of the PLL demodulation circuit can be minimized and the S / N ratio can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a satellite broadcast receiving tuner according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of temperature characteristics of a capture range of the PLL demodulation circuit 13.

FIG. 3 is a block diagram showing a configuration example of a conventional satellite broadcast receiving tuner.

FIG. 4 is a diagram for explaining changes in frequency characteristics of the BPF 6 with temperature.

5 is a diagram showing an example of temperature characteristics of a capture range of the PLL demodulation circuit 7. FIG.

[Explanation of symbols]

 3 Channel Selection Circuit 4 Local Oscillator 5 Mixer 6 BPF 7,13 PLL Demodulation Circuit 8,14 VCO 9 Phase Comparator 10 DC Amplifier 12 AFC Circuit 13 PLL Demodulation Circuit

Claims (1)

[Scope of utility model registration request] 1. A tuning circuit that outputs a tuning voltage according to a channel selected by a viewer, a local oscillator that outputs a local oscillation signal whose oscillation frequency is controlled by the tuning voltage, and a high-frequency signal. A mixer that mixes the local oscillation signal and converts it to an intermediate frequency signal, a bandpass filter that passes the intermediate frequency signal, a voltage controlled oscillator that outputs an oscillation signal of a predetermined frequency, and the intermediate frequency signal A phase comparator for comparing a phase with the phase of the oscillation signal to output a phase comparison signal, a DC amplifier for amplifying the phase comparison signal and controlling the frequency of the oscillation signal by the output signal, and the DC amplifier And an AFC circuit that outputs an AFC voltage by detecting the average DC voltage of the output signal of the AFC circuit. In a satellite broadcast receiving tuner that controls the oscillation frequency of the local oscillation signal so as to have a corresponding voltage, the temperature characteristic of the voltage controlled oscillator may be set to be substantially equal to the temperature characteristic of the bandpass filter. A characteristic satellite tuner.