JPH08289221A - Digital and analog sharing tuner - Google Patents

Abstract

PURPOSE: To make this tuner economically profitable with simple configuration and further to easily suppress the interference of signals to be exerted upon a circuit by guiding an analog modulated television signal through a first output terminal to an analog demodulating means and guiding a digital modulated television signal through a second output terminal to a digital demodulating means. CONSTITUTION: At a CATV tuner 11, the digital modulated television signal and the analog modulated television signal are inputted to an input terminal 12 in common and this tuner is respectively provided with an output terminal 29 for outputting the analog modulated television signal and an output terminal 39 for outputting the digital modulated television signal. Then, an analog demodulation circuit 31 for demodulating the analog modulated television signal and a digital demodulation circuit 43 for demodulating the digital modulated television signal are respectively connected to the respective output terminals 29 and 39. Thus, the CATV tuner 11 can be shared for digital processing and analog processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a digital / analog common tuner for selectively receiving a digitally modulated television signal and an analogly modulated television signal.

[0002]

2. Description of the Related Art In a conventional CATV (Cable Television) broadcasting system or the like, a television signal is transmitted, for example, to an NTSC (National Television System Committ) on the transmitting side.
ee) method and the like, and R is obtained as a result.
An F (Radio Frequency) signal is analog-transmitted to each subscriber via a cable. Then, on the receiving side, the received RF signal is transferred to the IF (Intermedia) by the CATV tuner.
te Frequency) band for demodulation.

FIG. 4 shows the configuration of such a conventional analog tuner. That is, reference numeral 11 is CATV
An RF signal obtained by receiving a CATV broadcast is supplied to the input terminal 12 of the tuner. The RF signal supplied to the input terminal 12 is limited to a predetermined level range by the attenuator 13, and then the RF amplification circuit 14
And is supplied to the first frequency conversion circuit 15.

The first frequency conversion circuit 15 is a VCO.
The input RF signal is frequency-converted into a first intermediate frequency signal based on the first local oscillation signal output from the (Voltage Control Oscilator) 16. In this case, V
The oscillation output signal of the CO 16 is output to the CA via the output terminal 17.
The frequency is supplied to the frequency dividing circuit 18 installed outside the TV tuner 11 to be frequency-divided, and then supplied to one input end of the phase comparison circuit 19.

The phase comparison circuit 19 compares the phase of the reference signal of a constant frequency supplied to the other input terminal through the input terminal 20 with the output signal of the frequency dividing circuit 18,
The phase error signal corresponding to the phase difference is output.
Then, the phase error signal output from the phase comparison circuit 19 is supplied to the VCO 16 from the input terminal 23 via the charge pump circuit 21 and the loop filter circuit 22, so that the phase difference V is eliminated.
The oscillation frequency of CO16 is controlled. As a result, by controlling the frequency division ratio of the frequency dividing circuit 18, it is possible to select a receiving channel.

Here, the first intermediate frequency signal output from the first frequency conversion circuit 15 is a BPF (Band P
Ass filter) 24 performs band filtering processing corresponding to the first intermediate frequency band, is amplified by IF amplification circuit 25, and is then supplied to second frequency conversion circuit 27 via BPF 26. This second frequency conversion circuit 27
The input signal is frequency-converted into a second intermediate frequency signal based on the second local oscillation signal output from the VCO 28.

The second intermediate frequency signal output from the second frequency conversion circuit 27 is supplied to the analog demodulation circuit 31 via the coaxial cable 30 connected to the output terminal 29 of the CATV tuner 11. Used for demodulation processing. In this case, the AFC (Automatic Frequency Control) signal generated by the analog demodulation circuit 31 is CA
It is supplied to the VCO 28 via the input terminal 32 of the TV tuner 11 and its oscillation frequency is controlled, so that AFC is performed for the offset of the input RF signal and the like.

By the way, in the recent CATV broadcasting system, in addition to analog modulation of the television signal, for example, 64QAM (Quadrature) is added to the television signal.
Amplitude Modulation) and 16VSB (Vestigial Si)
Digital modulation processing such as deband) is performed and digital transmission is performed to each subscriber. In other words, analog-modulated television signals and digitally-modulated television signals are being mixed and broadcast.

Therefore, even on the receiving side receiving the broadcast,
A tuner for digital / analog sharing that can selectively receive both an analog-modulated television signal and a digitally-modulated television signal is required. In this case, if the analog tuner for demodulating the analog-modulated television signal and the digital tuner for demodulating the digitally-modulated television signal are simply built in one cabinet, the configuration is Complicated, large and heavy.
The problem of becoming economically disadvantageous has arisen.

Further, in the case of considering a tuner for both digital and analog, a circuit for handling an analog signal and a circuit for handling a digital signal are installed close to each other, so that the interference of both signals on each other's circuits is suppressed. It is indispensable to take measures for this, but there is also the inconvenience that it is very difficult to realize this measure at a level where it can be put to practical use.

[0011]

As described above, the conventional digital / analog common tuner has a complicated structure, is liable to be large in size, and is economically disadvantageous. There is a problem that it is difficult to suppress the interference.

Therefore, the present invention has been made in consideration of the above circumstances, and is extremely advantageous in that it has a simple structure and is economically advantageous, and furthermore, it is possible to easily suppress the interference of a signal on a circuit, which is an excellent digital / analog common use. The purpose is to provide a tuner.

[0013]

SUMMARY OF THE INVENTION A digital / analog common tuner according to the present invention provides an input terminal to which an analog-modulated television signal and a digitally-modulated television signal are commonly supplied, and to this input terminal. Frequency conversion means for converting the generated television signal into an intermediate frequency signal, a first output end for guiding the intermediate frequency signal output from the frequency conversion means to the analog demodulation means, and an intermediate frequency output from the frequency conversion means And a second output end for guiding the signal to the digital demodulation means.

[0014]

According to the above construction, the analog-modulated television signal is guided to the analog demodulating means through the first output end, and the digitally-modulated television signal is passed through the second output end. Since the signal is guided to the digital demodulation means, the frequency conversion means can be used for both digital processing and analog processing, which simplifies the configuration and is economically advantageous. It is possible to suppress the interference of the signal on the analog circuit and the digital circuit.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. 1, the same parts as those in FIG. 4 are designated by the same reference numerals. First, CA
A structure in which a frequency dividing circuit 18, a phase comparison circuit 19, a charge pump circuit 21, and a loop filter circuit 22 for controlling the oscillation frequency of the VCO 16 which are external to the TV tuner 11 are built in the CATV tuner 11. Has become.

The oscillation output signal of the VCO 28 is
The signal is supplied to the frequency dividing circuit 33 built in the CATV tuner 11 to be frequency-divided, and then supplied to one input end of the phase comparison circuit 34. This phase comparison circuit 34 has an input terminal 35.
The reference signal of a constant frequency supplied to the other input terminal via the output signal of the frequency dividing circuit 33 is compared in phase, and a phase error signal corresponding to the phase difference is output.

The phase error signal output from the phase comparison circuit 34 is supplied to the VCO 28 via the charge pump circuit 36 and the loop filter circuit 37, so that the phase difference is eliminated.
The oscillation frequency of 28 is controlled.

Further, the second intermediate frequency signal output from the second frequency conversion circuit 27 is supplied to the distribution circuit 38 and is of a pin type with the coaxial type output terminal 29 installed in the CATV tuner 11. It is supplied to the output terminals 39 and 39, respectively. Of these, the second intermediate frequency signal supplied to the coaxial output terminal 29 is supplied to the analog demodulation circuit 31 via the coaxial cable 30 as described above.

The pin-type output terminal 39 is connected to a circuit pattern 41 formed on the printed wiring board 40 by solder 42. A pin type input terminal 44 provided in the digital demodulation circuit 43 is connected to the circuit pattern 41 of the printed wiring board 40 by solder 45. Therefore, the second intermediate frequency signal supplied to the pin-type output terminal 39 is supplied to the digital demodulation circuit 43 via the circuit pattern 41 of the printed wiring board 40 and used for demodulation processing.

Therefore, according to the configuration of the above embodiment, in the CATV tuner 11, the digitally modulated television signal and the analogly modulated television signal are commonly input to the input terminal 12, and the analog signal is input. An output terminal 29 for outputting a modulated television signal and an output terminal 39 for outputting a digitally modulated television signal are provided respectively, and the output terminals 29, 3 are provided.
Since the analog demodulation circuit 31 for demodulating the analog-modulated television signal and the digital demodulation circuit 43 for demodulating the digital-modulated television signal are connected to each other, the CATV tuner 11 is subjected to digital processing. It can be shared with analog processing, which simplifies the configuration and is economically advantageous.

Further, since the output terminal 29 for outputting the analog-modulated television signal is of the coaxial type, the external noise can be suppressed by the shield effect of the outer conductor and the digitally-modulated television can be suppressed. Since the output terminal 39 for outputting a signal is of a pin type, it is easy to connect to the printed wiring board 40 having a large-scale digital signal processing circuit. Then, the interference of the digital signal and the analog signal on the analog demodulation circuit 31 and the digital demodulation circuit 43 can be easily suppressed.

Here, V for generating the first local oscillation signal
Frequency divider circuit 1 for controlling the oscillation frequency of CO16
8, PLL (Phase Locked L) including a phase comparison circuit 19, a charge pump circuit 21, and a loop filter circuit 22.
oop) circuit and VCO2 for generating the second local oscillation signal
The PLL circuit including the frequency dividing circuit 33, the phase comparison circuit 34, the charge pump circuit 36, and the loop filter circuit 37 for controlling the oscillation frequency of 8 is built in the CATV tuner 11.

In general, when receiving a digitally modulated television signal, the phase noise performance of the VCOs 16 and 28 required for the CATV tuner 11 is the same as that of a conventional analog tuner that receives only an analog modulated television signal. In comparison, very low noise performance is required.
Therefore, the phase comparison frequency in the PLL circuit that controls the VCOs 16 and 28 is selected as high as possible.

Further, in order to keep good demodulation performance from shock noise or the like given to the tuner body from the outside, V
The bandwidth of the loop in the PLL circuit that controls the COs 16 and 28 needs to be set as wide as possible. However, if the bandwidth of the loop is set wide, the side spurious performance of the phase comparison frequency generated in the PLL circuit deteriorates, and the phase noise performance also deteriorates. CATV for receiving digitally modulated television signals
The phase noise performance required for the VCOs 16 and 28 of the tuner 11 has such conflicting requirements.

It is needless to say that the VCO 16 and 28 are required to have a certain degree of phase noise performance and low spurious performance when receiving an analog-modulated television signal.

Therefore, when the analog-modulated television signal is received in the digital / analog common tuner, there is a problem that the side spurious of the phase comparison frequency generated in the PLL circuit causes the deterioration of the image quality, and the low phase. It is difficult to achieve both noise performance and suppression of side spurs at the phase comparison frequency required when receiving an analog-modulated television signal.

In other words, in each PLL circuit, when the frequency of the reference signal given to the phase comparison circuits 19 and 34 is f, as shown in FIG. Side spurs are generated. On the other hand, if there is spurious in the reception band, the sensitivity of the interference given to the image signal may differ due to the frequency difference between the frequency of the image carrier and the frequency of the spurious when receiving the analog-modulated television signal. Are known. Therefore, when an analog-modulated television signal is received, the frequency is set so that there is little interference due to side spurs of the phase comparison frequency, and it is set to a value other than an integral multiple of the horizontal synchronizing frequency of the television signal.

For setting the phase comparison frequency in such a PLL circuit, an appropriate value can be selected based on the W curve shown in FIG. As described above, in the CATV tuner 11, the phase comparison frequency in the PLL circuit should be set to a frequency that causes less interference when receiving the analog-modulated television signal and is not an integral multiple of the horizontal synchronizing frequency of the television signal. As a result, it is possible to reduce the interference of side spurs of the phase comparison frequency in the PLL circuit on the analog-modulated television signal.

In particular, the phase comparison frequencies in the PLL circuit are set to 2 MHz, 1 MHz, 500 kHz, 125
kHz, 62.5 kHz, 31.5 kHz, 15.62
When any value of 5 kHz is set, the side spurs of the phase comparison frequency in the PLL circuit are converted into analog modulated television signals while maintaining the low phase noise which is an important performance item for digital reception. The interference given can be reduced. The present invention is not limited to the above embodiments, and various modifications can be carried out without departing from the scope of the invention.

[0030]

As described above in detail, according to the present invention,
It is possible to provide a very good digital / analog common tuner that has a simple structure, is economically advantageous, and can easily suppress the interference of a signal on a circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a digital / analog common tuner according to the present invention.

FIG. 2 is a diagram for explaining side spurs of a phase comparison frequency in a PLL circuit.

FIG. 3 is a diagram showing a W curve for selecting a phase comparison frequency in a PLL circuit.

FIG. 4 is a block configuration diagram showing a conventional analog tuner.

[Explanation of symbols]

11 ... CATV tuner, 12 ... Input terminal, 13 ... Attenuator, 14 ... RF amplification circuit, 15 ... First frequency conversion circuit, 16 ... VCO, 17 ... Output terminal, 18 ... Dividing circuit, 19 ... Phase comparison circuit, 20 ... Input terminal, 21 ... Charge pump circuit, 22 ... Loop filter circuit, 23 ... Input terminal, 24 ... BPF, 25 ... IF amplifier circuit, 26 ... B
PF, 27 ... Second frequency conversion circuit, 28 ... VCO, 2
9 ... Output terminal, 30 ... Coaxial cable, 31 ... Analog demodulation circuit, 32 ... Input terminal, 33 ... Frequency divider circuit, 34 ... Phase comparison circuit, 35 ... Input terminal, 36 ... Charge pump circuit, 37 ... Loop filter circuit, 38 ... Distribution circuit, 39
... output terminal, 40 ... printed wiring board, 41 ... circuit pattern,
42 ... Solder, 43 ... Digital demodulation circuit, 44 ... Input terminal, 45 ... Solder.

Claims (2)

[Claims] 1. An input terminal to which an analog modulated television signal and a digitally modulated television signal are commonly supplied, and a frequency conversion for converting the television signal supplied to this input terminal to an intermediate frequency signal. Means, a first output terminal for guiding the intermediate frequency signal output from the frequency converting means to the analog demodulating means, and a second output terminal for guiding the intermediate frequency signal output from the frequency converting means to the digital demodulating means. A digital / analog common tuner characterized by comprising: 2. The tuner according to claim 1, wherein the first output end is a coaxial type terminal and the second output end is a pin type terminal.