JP3810848B2 - Digital tuner - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital tuner for receiving a digitally modulated signal in a CATV (cable television) receiver or a satellite broadcast receiver.
[0002]
[Prior art]
As is well known, in recent years, broadcasting services such as satellite broadcasting and CATV have become widespread in addition to current broadcasting such as analog-modulated NTSC, and digital broadcasting has started. Is about to be offered. This digital broadcast is a broadcast by a digitally modulated television signal such as QPSK (Quadrature Phase Shift Keying), 64QAM (Quadrature Amplitude Modulation), or 16VSB (Vestigial Side Band).
[0003]
Here, in CATV broadcasting, for example, a digitally modulated wide band high frequency signal of usually about 50 to 750 MHz is transmitted to each home via a cable. The high frequency signal is converted into a frequency band called an intermediate frequency (44 MHz ± 3 MHz in the United States) by frequency conversion once or twice in a tuner provided in a receiving device such as a CATV terminal device in each home. Thereafter, the interference wave is suppressed by, for example, a surface acoustic wave filter. The intermediate frequency band signal whose interference wave is suppressed by this surface acoustic wave filter is either a frequency conversion circuit that converts the frequency to a frequency band centered on an integer multiple of the data rate of the digital modulation wave, or a quadrature detection circuit. Frequency conversion or quadrature detection is performed by one circuit. The frequency-converted or quadrature-detected signal is subjected to digital demodulation such as QPSK, 64QAM, or 16VSB. The same applies to satellite broadcasting.
[0004]
FIG. 7 shows a digital tuner used in such a conventional receiving apparatus. That is, reference numeral 11 in the figure is a main board, on which a first housing 12, a second housing 13, and a digital demodulation circuit 14 are provided. Among them, the first casing 12 and the second casing 13 are arranged with a plurality of (four in the illustrated case) terminals exposed on the respective side surfaces, and are fixed to the main board 11 and fixed. Electrical contact is intended. The digital demodulation circuit 14 is configured by an integrated circuit, a capacitor, and the like.
[0005]
That is, in the first casing 12, for example, a wideband digitally modulated high frequency signal S 1 is supplied to the input terminal 15. The high frequency signal S1 supplied to the input terminal 15 is supplied to one input terminal of the first frequency converter 16 configured by a diode or the like. A local oscillation signal S 2 output from the local oscillator 17 is supplied to the other input terminal of the first frequency converter 16. The first frequency converter 16 calculates the high frequency signal S1 and the local oscillation signal S2, and obtains a frequency corresponding to the calculation result as the first intermediate frequency signal S3.
[0006]
Then, the first intermediate frequency signal S3 output from the first frequency converter 16 is supplied to one input terminal of the second frequency converter 18. A local oscillation signal S 4 output from the local oscillator 19 is supplied to the other input terminal of the second frequency converter 18. The second frequency converter 18 calculates the first intermediate frequency signal S3 and the local oscillation signal S4, and obtains a frequency corresponding to the calculation result as the second intermediate frequency signal S5. Then, the second intermediate frequency signal S5 output from the second frequency converter 18 is supplied to the second casing 13 via the output terminal 20.
[0007]
The output terminal 20 in the first housing 12 and the input terminal 21 in the second housing 13 are electrically connected via a copper foil pattern 22 provided on the main substrate 11. In the second housing 13, the second intermediate frequency signal S 5 supplied to the input terminal 21 is supplied to a BPF (Band Pass Filter) 23. The BPF 23 suppresses interference waves in the second housing 13.
[0008]
The second intermediate frequency signal S6 that has passed through the BPF 23 is supplied to one input terminal of the third frequency converter 24. A local oscillation signal S 7 output from the local oscillator 25 is supplied to the other input terminal of the third frequency converter 24. The third frequency converter 24 calculates the second intermediate frequency signal S6 and the local oscillation signal S7. In this calculation, frequency conversion is performed to a baseband frequency band centered on a frequency that is a multiple of the data rate of the digital modulation wave with respect to the second intermediate frequency signal S6. In general, about 5 MHz, which is one times the digital modulation wave data rate, is often used as the baseband frequency band.
[0009]
The signal S8 frequency-converted to the baseband frequency band is supplied to the digital demodulation circuit 14 via the output terminal 131. In the second casing 13, frequency conversion is performed by the third frequency converter 24. However, instead of the third frequency converter 24, quadrature detection may be performed by a quadrature detection circuit. Good. The output terminal 131 and the digital demodulation circuit 14 are electrically connected through a copper foil pattern 26 provided on the main board 11.
[0010]
Then, the digital demodulation circuit 14 performs digital demodulation processing such as QPSK, 64QAM, or 16VSB on the signal S8 frequency-converted or quadrature-detected by the second casing 13.
[0011]
By the way, the interference wave in the second casing 13 is suppressed by the BPF 23. As the BPF 23, a surface acoustic wave filter that can sufficiently suppress adjacent channels and has excellent group delay characteristics in the band is used.
[0012]
However, the surface acoustic wave filter has an insertion loss of 20 dB or more. For this reason, the signal level of the second intermediate frequency signal S6 that has passed through the surface acoustic wave filter becomes weak, and the input / output impedance of the surface acoustic wave filter is very high. This is disadvantageous for radio wave radiation and diving. Furthermore, the surface acoustic wave filter has a time delay of about 1 μs.
[0013]
Here, problems caused by various characteristics of the surface acoustic wave filter will be described. In other words, if separation between the surface acoustic wave filter and the input / output connection line of the surface acoustic wave filter and other circuits is insufficient, radio waves may be radiated from the line, or unnecessary radio waves, that is, noise, etc. may jump into the line. become. For this reason, ripples are generated in the amplitude characteristics in the pass band, amplitude characteristics (attenuation) outside the pass band are deteriorated, group delay characteristics in the pass band are deteriorated, and spurious is generated in the digital demodulation circuit 14. Will end up.
[0014]
Further, since the output terminal 20 of the first housing 12 and the input terminal 21 of the second housing 13 are exposed and connected on the main board 11, a mismatch occurs on the connection, and the connection When radio waves are radiated or unwanted radio waves jump into the line, that is, the copper foil pattern 22, ripples are generated in the amplitude characteristics in the passband of the surface acoustic wave filter.
[0015]
In addition, when the quadrature detection circuit is accompanied, a level difference is generated between two output terminals having a quadrature phase or a phase error is generated due to radio wave radiation or jumping. This is because, when a gain control circuit is accompanied in the intermediate frequency band, the level difference between the front and rear stages of the gain control circuit becomes large, thereby increasing the influence of radio wave radiation and jumping.
[0016]
[Problems to be solved by the invention]
As described above, in the conventional digital tuner, the output terminal of the first housing and the input terminal of the second housing are connected by the line exposed on the main board, and the surface acoustic wave filter and other circuits are connected. Because of the direct connection, the connection band and imperfect separation of the surface acoustic wave filter from other circuits cause radio waves to radiate and jump into the connection line. , The external amplitude characteristics, group delay characteristics, spurious characteristics, etc. are adversely affected.
[0017]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the connection relationship between a plurality of housings and bandpass filters and other circuits, as well as the amplitude characteristics, group delay characteristics, and spurious characteristics within and outside the passband of the bandpass filters. It is an object of the present invention to provide a digital tuner with good reception characteristics.
[0018]
[Means for Solving the Problems]
A digital tuner according to the present invention is a tuner for receiving a digitally modulated signal,
A housing having first and second shield plates that are sheet-like members;
In the housing, an input terminal that supplies a wideband signal, and a first frequency conversion unit that converts the wideband signal supplied to the input terminal into an intermediate frequency signal by performing frequency conversion at least once. A band-pass filter having the same passband as the intermediate frequency signal frequency-converted by the first frequency converter and passing the intermediate frequency signal; and an intermediate frequency signal passed through the bandpass filter, And a second frequency converter that converts the frequency to a frequency band centered on a frequency that is an integral multiple of the data rate of the digital modulated wave corresponding to the frequency signal.
[0019]
The casing is divided into first, second, and third rooms by the first and second shield plates, and the first frequency converter is provided in the first chamber that is in contact with the first shield plate. The bandpass filter is accommodated in the second room in contact with the first and second shield plates, and the second frequency converter is accommodated in the third room in contact with the second shield plate. Yes.
[0020]
According to this configuration, the first frequency converter, the band-pass filter, and the second frequency converter are housed in one housing, and the band-pass filter is independent of other circuits using two shield plates. Therefore, the connection mismatch and the incomplete separation from the other circuits with respect to the band-pass filter are eliminated. For this reason, ripples of amplitude characteristics in the pass band, deterioration of amplitude characteristics outside the pass band, and deterioration of group delay characteristics in the pass band can be suppressed, and good reception characteristics can be obtained.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an embodiment of the present invention.
In FIG. 1, reference numeral 27 in the drawing denotes a casing, which includes shield plates 28 and 29 that are at least two sheet-like members. The casing 27 is divided into three rooms 30, 31, 32 by two shield plates 28, 29. Note that the two shield plates 28 and 29 are formed by cutting and raising from the casing 27 or inserted into cutout portions provided in the casing 27. These shield plates 28 and 29 serve to flow unnecessary radio waves and the like generated from the track to the ground.
[0022]
The casing 27 includes a first frequency converter 33a, a local oscillator 33b, a second frequency converter 33c, and a first chamber 30 that are in contact with the first shield plate 28. A local oscillator 33d is provided. The casing 27 includes a surface acoustic wave filter 34 and a working circuit 35 that are band-pass filters in a second chamber 31 in contact with the first shield plate 28 and the second shield plate 29. . Further, the casing 27 is provided with a third frequency converter 36 and a local oscillator 37 in a third chamber 32 in contact with the second shield plate 29.
[0023]
That is, in the casing 27, for example, the broadband digitally modulated high frequency signal S9 supplied to the input terminal 38 is supplied to one input terminal of the first frequency converter 33a. A local oscillation signal S10 generated from the local oscillator 33b is supplied to the other input terminal of the first frequency converter 33a. The first frequency converter 33a calculates the high frequency signal S9 and the local oscillation signal S10, and obtains a frequency corresponding to the calculation result as the first intermediate frequency signal S11.
[0024]
Then, the first intermediate frequency signal S11 output from the first frequency converter 33a is supplied to one input terminal of the second frequency converter 33c. A local oscillation signal S12 generated from the local oscillator 33d is supplied to the other input terminal of the second frequency converter 33c. The second frequency converter 33c calculates the first intermediate frequency signal S11 and the local oscillation signal S12, and obtains a frequency corresponding to the calculation result as the second intermediate frequency signal S13. The second intermediate frequency signal S13 output from the second frequency converter 33c is supplied to the second room 31 via the first shield plate 28.
[0025]
In the second room 31, the second intermediate frequency signal S13 output from the second frequency converter 33c is supplied to the surface acoustic wave filter. The surface acoustic wave filter 34 suppresses interference waves in the housing 27. The second intermediate frequency signal S14 that has passed through the surface acoustic wave filter 34 is supplied to the operating circuit 35. The operation circuit 35 is a circuit that operates in the same frequency band as the pass band of the surface acoustic wave filter 34. The second intermediate frequency signal S15 output from the operating circuit 35 is supplied to the third room 32 via the second shield plate 29.
[0026]
In the third room 32, the second intermediate frequency signal S15 is supplied to one input end of the third frequency converter 36. A local oscillation signal S <b> 16 generated from the local oscillator 37 is supplied to the other input terminal of the third frequency converter 36. The third frequency converter 36 calculates the second intermediate frequency signal S15 and the local oscillation signal S16. The calculation here performs frequency conversion to a baseband frequency band centered on a frequency that is an integral multiple of the data rate of the second intermediate frequency signal S15. The signal S17 frequency-converted to the baseband frequency band is taken out from the output terminal 39.
[0027]
Therefore, according to the above-described embodiment, the tuner unit 33, the surface acoustic wave filter 34, the operating circuit 35, the third frequency converter 36, and the local oscillator 37 are housed in one housing, and further, two shields Since the surface acoustic wave filter 34 and the operating circuit 35 are housed in one room independently of the other circuits using the plates 28 and 29, the connection mismatch and the surface acoustic wave filter 34 are inconsistent with the other circuits. Complete separation is eliminated. For this reason, ripples of amplitude characteristics in the pass band, deterioration of amplitude characteristics outside the pass band, and deterioration of group delay characteristics in the pass band can be suppressed, and good reception characteristics can be obtained. In the above embodiment, a line for supplying power to another circuit may be included.
[0028]
FIG. 2 shows a second embodiment of the present invention.
In FIG. 2, the same parts as those in FIG. The difference from FIG. 1 is that the input terminal of the surface acoustic wave filter 34 is a balanced input terminal. That is, the surface acoustic wave filter 34 is connected to the output of the tuner unit 33 by a balanced line.
[0029]
That is, according to the second embodiment, the radio waves radiated from the balanced input terminal of the surface acoustic wave filter 34 have opposite phases to each other, and the phases cancel each other even if they jump into the unbalanced output terminal. The effects of the first shield plate 28 described in the embodiment are further enhanced, and ripples in the amplitude characteristics within the pass band caused by radio wave radiation and jumps, deterioration of amplitude characteristics (attenuation) outside the pass band, Degradation of the group delay characteristic in the pass band is suppressed, and good reception characteristics can be obtained. The surface acoustic wave filter 34 can obtain the same effect even if it is connected to the input of the operating circuit 35 by a balanced line.
[0030]
FIG. 3 shows a third embodiment of the present invention.
In FIG. 3, the same parts as those in FIG. The difference from FIG. 2 is that a gain control circuit 40 is interposed between the operating circuit 35 and the third frequency converter 36. Further, the second room 31 is divided into two rooms 31 a and 31 b by the third shield plate 41. The surface acoustic wave filter 34 is accommodated in one room 31a, and the operation circuit 35 and the gain control circuit 40 are accommodated in the other room 31b.
[0031]
That is, the gain control circuit 40 performs gain control on the second intermediate frequency signal S15 and adjusts the level of the second intermediate frequency signal S15 so that the output becomes constant. The signal S18 adjusted by the gain control circuit 40 is supplied to one input terminal of the third frequency converter 36.
[0032]
That is, according to the third embodiment, the level of the second intermediate frequency signal S15 is adjusted by the gain control circuit 40, and the second chamber 31 is further divided by the third shield plate 41, thereby gain control. The circuit 40 is made independent. For this reason, it is possible to reduce the influence of radio wave emission and jump due to an increase in the level difference between the front and rear stages of the gain control circuit 40, and thereby the amplitude characteristics in the passband generated by the radio wave emission and jump are reduced. Ripple, amplitude characteristics (attenuation) outside the passband, and group delay characteristics inside the passband are prevented from deteriorating, and good reception characteristics can be obtained.
[0033]
FIG. 4 shows a fourth embodiment of the present invention.
In FIG. 4, the same parts as those in FIG. The difference from FIG. 3 is that the output of the third frequency converter 36 is supplied to the digital demodulation circuit 42 instead of the output terminal 39. The digital demodulation circuit 42 is housed in the housing 27. The digital demodulation circuit 42 performs digital demodulation processing such as QPSK, 64QAM, or 16VSB on the signal S17 output from the third frequency converter 36.
[0034]
That is, according to the fourth embodiment, since the digital demodulation circuit 42 is housed in the same casing 27 as the other circuits, the connection portion between the third frequency converter 36 and the digital demodulation circuit 42 Can be prevented from being exposed to the outside, and adverse effects due to connection mismatch can be prevented. For this reason, the occurrence of spurious from the digital demodulation circuit 42 can be reduced, and good reception characteristics can be obtained.
[0035]
FIG. 5 shows a fifth embodiment of the present invention.
In FIG. 5, the same parts as those in FIG. The difference from FIG. 3 is that a quadrature detection circuit 43 is housed in the third room 32 in place of the third frequency converter 36 and the local oscillator 37. The quadrature detection circuit 43 includes mixers 431 and 432, a local oscillator 433, and phase coefficient units 434 and 435.
[0036]
That is, the second intermediate frequency signal S18 whose level is adjusted by the gain control circuit 40 is supplied to one input terminal of each of the mixers 431 and 432, respectively. Signals S20 and S21 output from the phase coefficient units 434 and 435 are supplied to the other input ends of the mixers 431 and 432, respectively. Local oscillation signals S22 and S23 generated from the local oscillator 433 are supplied to the phase coefficient units 434 and 435.
[0037]
First, the local oscillator 433 supplies the local oscillation signals S22 and S23 to the phase coefficient unit 434 that does not shift the phase and the coefficient unit 435 that shifts the phase by 90 degrees. Then, the signals S20 and S21 output from the phase coefficient units 434 and 435 are supplied to the other input terminals of the mixers 431 and 432, respectively.
[0038]
On the other hand, the mixer 431 calculates the second intermediate frequency signal S18 and the signal S20, and supplies the calculation result to the output terminal 44 as the third intermediate frequency signal S24. The mixer 432 calculates the second intermediate frequency signal S18 and the signal S21, and supplies the calculation result to the output terminal 45 as a third intermediate frequency signal S25 having a phase of 90 degrees.
[0039]
That is, according to the fifth embodiment, since the quadrature detection circuit 43 is housed in the third room 32 of the housing 27 so as to be independent, 2 having a quadrature phase due to radio wave radiation or jumping in. The level difference and the phase error generated between the two output terminals 44 and 45 can be reduced, and good reception characteristics can be obtained.
[0040]
FIG. 6 shows a sixth embodiment of the present invention.
In FIG. 6, the same parts as those in FIG. The difference from FIG. 3 is that the second room 31 and the third room 32 are both in contact with the first room 30 via the first shield plate 28.
[0041]
That is, according to the sixth embodiment, the same effect as in the first embodiment can be obtained.
As described above, in each embodiment, the casing 27 is divided into three to five rooms, but a plurality of rooms are provided using a plurality of shield plates so that each circuit is independent. It may be.
In addition, this invention is not limited to said each embodiment, In addition, it can implement in various deformation | transformation in the range which does not deviate from the summary.
[0042]
【The invention's effect】
As described above in detail, according to the present invention, the connection relationship between a plurality of housings and the band-pass filter and other circuits is improved, and the amplitude characteristics inside and outside the pass band of the band-pass filter and the group delay are improved. It is possible to provide a digital tuner with improved characteristics and spurious characteristics and with good reception characteristics.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram showing an embodiment of a digital tuner according to the present invention.
FIG. 2 is a block diagram showing a second embodiment of the present invention.
FIG. 3 is a block configuration diagram showing a third embodiment of the present invention.
FIG. 4 is a block configuration diagram showing a fourth embodiment of the present invention.
FIG. 5 is a block configuration diagram showing a fifth embodiment of the present invention.
FIG. 6 is a block configuration diagram showing a sixth embodiment of the present invention.
FIG. 7 is a perspective view showing a conventional digital tuner.
[Explanation of symbols]
27 ... Case,
28 ... first shield plate,
29 ... the second shield plate,
30 ... the first room,
31 ... second room,
31a ... room,
31b ... room,
32 ... The third room,
33 ... tuner section,
33a ... first frequency converter,
33b ... Local oscillator,
33c-second frequency converter,
33d ... Local oscillator,
34 ... surface acoustic wave filter,
35 ... operating circuit,
36 ... a third frequency converter,
37 ... Local oscillator,
38 ... Input terminal,
39: Output terminal,
40. Gain control circuit,
41 ... Third shield plate,
42: Digital demodulation circuit,
43 ... Quadrature detection circuit,
431 ... Mixer,
432 ... a mixer,
433 ... a local oscillator,
434 ... Phase coefficient device,
435 ... Phase coefficient device,
44 ... Output terminal,
45: Output terminal.

Claims (5)

A tuner for receiving a digitally modulated signal,
A housing having first and second shield plates that are sheet-like members;
In the housing,
An input terminal for supplying a broadband signal;
A first frequency conversion unit that converts the wideband signal supplied to the input terminal into a first intermediate frequency signal by performing frequency conversion;
A second frequency converter that converts the first intermediate frequency signal into a second intermediate frequency signal by performing frequency conversion on the first intermediate frequency signal;
A bandpass filter having the same passband as the second intermediate frequency signal frequency-converted by the second frequency converter, and passing the second intermediate frequency signal;
A third frequency converter that converts the frequency of the second intermediate frequency signal that has passed through the band-pass filter;
A gain control circuit that is connected between the band-pass filter and the third frequency converter and adjusts the level of the second intermediate frequency signal to be constant;
The housing is divided into first, second, and third rooms by the first and second shield plates, and the first frequency converter and the second frequency are provided in the first room. accommodating the conversion unit, and wherein the second room the band-pass filter and said gain control circuit is accommodated in, and adapted to house the front Symbol third frequency converting unit in the third chamber Digital tuner. A tuner for receiving a digitally modulated signal,
A housing having first and second shield plates that are sheet-like members;
In the housing,
An input terminal for supplying a broadband signal;
A first frequency converter that converts the wideband signal supplied to the input terminal into a first intermediate frequency signal by performing frequency conversion;
A second frequency converter that converts the first intermediate frequency signal into a second intermediate frequency signal by performing frequency conversion on the first intermediate frequency signal;
A bandpass filter having the same passband as the second intermediate frequency signal frequency-converted by the second frequency converter, and passing the second intermediate frequency signal;
A quadrature detection unit that quadrature-detects the second intermediate frequency signal that has passed through the band-pass filter;
A gain control circuit that is connected between the band-pass filter and the quadrature detection unit and adjusts the level of the second intermediate frequency signal to be constant;
The housing is divided into first, second, and third rooms by the first and second shield plates, and the first frequency converter and the second frequency are provided in the first room. housing a conversion unit, said second accommodating the band-pass filter and said gain control circuit in the room, a digital tuner, characterized in that so as to house the front Symbol quadrature detector in the third chamber . The housing further includes a third shield plate that is a sheet-like member,
The digital tuner according to claim 1, wherein the band-pass filter and the gain control circuit are partitioned by the third shield plate. The housing further includes a third shield plate that is a sheet-like member,
3. The digital tuner according to claim 2, wherein the band-pass filter and the gain control circuit are partitioned by the third shield plate. 2. The digital tuner according to claim 1, further comprising a digital demodulation circuit for digitally demodulating an output signal of the third frequency converter in the third room in the casing.

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