JP2000068752A - Receiver for digital broadcasting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver of simple constitution capable of suppressing the interference of reception by easily removing an image signal from a received digital broadcasting signal. SOLUTION: The down converting circuit 5b of this receiver 1 is made to be an image rejection type mixer. The desired signal of a frequency fD outputted from a high frequency amplifier circuit 4 is inputted to the circuit 5b to be mixed with the oscillation signal of a frequency fL0 from a local oscillator 5a to generate low IF(intermediate frequency) of a frequency fIF=fL0-fD. On the other hand, an image signal with an image frequency fIM inputted to the circuit 5b is shifted to a frequency fIM+fL0 to being removed state. Since the signal of the frequency fIM+fL0 is sufficiently separated from a frequency fIF of low IF compared with the image frequency fIM, frequency components related with the image signal is completely removed by passing through a band pass filter 6 of a poststage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcast receiver for receiving a broadcast transmitted by a digital modulation method, in particular, a television broadcast.

[0002]

2. Description of the Related Art In recent years, as an alternative to conventional analog television broadcasting, digital television broadcasting which provides television broadcasting with digitally modulated signals has attracted attention. On the receiver side of such a digital television broadcast, a received signal is converted into an intermediate frequency by the superheterodyne method.

FIG. 4 is a block diagram showing an example of the configuration of a digital broadcast receiver 101 of the single conversion type. FIG. 1 shows only a portion related to a main signal flow. The receiving process in the digital broadcast receiver 101 will be described below. First, the antenna 102
Of the digital broadcast signal input to the receiver, a desired frequency band, that is, a desired signal is selected by a tracking bandpass filter 103 capable of changing a center frequency in conjunction with a reception frequency, and is amplified by an RF amplifier 104. Its output is the tracking bandpass filter 1
After being further band-limited at 05, the signal is input to the down-conversion circuit 107 and mixed with an oscillation signal generated by the local oscillator 106 to produce an intermediate frequency (hereinafter referred to as IF).
Becomes

[0004] The IF obtained here corresponds to the input to the analog detection circuit in the case of analog broadcast reception.
Speaking of video signals, for example, in the United States, 45.
The frequency is set to 75 MHz, and 58.75 MHz in Japan. In the case of digital broadcast reception, it is very difficult to perform sampling at this frequency, and it is necessary to convert to a lower IF of a lower frequency, as is well known.

To obtain a low IF, the IF is further input to a band-pass filter 108 to remove unnecessary signals, then amplified by an IF amplifier 109, input to a down-conversion circuit 111, and generated by a local oscillator 110. Mix with the oscillation signal. This Low IF is input to the band-pass filter 112 to remove unnecessary signals,
Amplified by the low IF amplifier 113, the low IF
Output. Then, the signal is input to a detection circuit (not shown), detection is performed, and the A / D conversion process of the video signal is continued.

Next, FIG. 5 shows an example of the configuration of a digital broadcast receiver 121 of the double conversion type. FIG. 3 also shows only the part related to the main signal flow.
The receiving process in the digital broadcast receiver 121 will be described below. First, in the digital broadcast signal input to the antenna 122, only the frequency component to be received is selected by the wideband band-pass filter 123 that allows only the frequency to be received, and then the wideband amplifier 124
Is amplified by The output is input to an up-conversion circuit 126, mixed with a signal generated by a local oscillator 125, and mixed with a first intermediate frequency (hereinafter, 1st intermediate frequency).
IF).

[0007] The frequency of the first IF is fixed, and the desired reception channel is adjusted to be the frequency of the first IF by changing the frequency of the oscillation signal generated by the local oscillator 125. The 1st IF thus obtained is input to the band-pass filter 127 to remove unnecessary frequency components.
The signal is amplified by the amplifier 128. Then, the signal is input to the band-pass filter 129 and further band-limited, and then input to the down-conversion circuit 131. The down-conversion circuit 131 mixes the oscillation signal generated by the local oscillator 130 with a second intermediate frequency (hereinafter referred to as a second intermediate frequency).
F).

[0008] Like the above-mentioned IF, the 2nd IF is a low frequency Low for receiving digital broadcasting.
It is necessary to convert to IF. Therefore, this 2nd IF
Is further input to a band-pass filter 132 to remove unnecessary signals and is amplified by a second IF amplifier 133. The amplified signal is then input to a down-conversion circuit 135 and a local oscillator 134
Is mixed with the oscillation signal generated in step (1) to obtain a low IF. The low IF further includes a band-pass filter 13.
After the unnecessary signal is removed by 6, the signal is amplified by the Low IF amplifier 137 and becomes a Low IF output. Then, the signal is input to a detection circuit (not shown), detection is performed, and the A / D conversion process of the video signal is continued.

[0009]

A mixer circuit such as the down-converting circuits 107, 111, 131, 135 and the up-converting circuit 126 converts the received signal into IF, 1st IF, 2nd IF, or Low.
When the frequency is converted to IF, the RF frequency of the desired signal input to these mixer circuits is set to f _IN , and the local oscillator 106
The oscillation frequency of 110, 125, 130, 134 is f _LO , and the frequency of the frequency-converted signal (each intermediate frequency) is f
_{Assuming IF} , a relationship of f _IF = f _LO −f _IN holds. However, the image frequency f which has a relationship of f _IF = f _IM −f _LO
An image signal having an _IM accompanies and causes reception interference. FIG. 6 shows the relationship between the above frequencies. As can be seen from the figure, the image frequency f _IM has a mirror relationship with the frequency f _{IN of the} input signal with respect to the oscillation frequency f _LO of the local oscillator. Since the image signal must be removed before input to the mixer circuit, a trap circuit for removing the image signal is usually formed and attenuated.

The digital broadcast receiver 121 of the double conversion type is superior to the digital broadcast receiver 101 of the single conversion type in the function of suppressing such image disturbance. In the digital broadcast receiver 101, the desired RF frequency channel signal is immediately converted to an IF having a low frequency, so that f _IN +2
An image frequency f _IM of f _IF will be present on another RF frequency channel. Thus, the level of the image interference signal is very high and very difficult to remove. Further, in the digital broadcast receiver 101, since all band-pass filters preceding the mixer circuit are tracking band-pass filters, it is very difficult to form a high-performance image trap in all reception channels, and image interference characteristics It can be said that it is a weak circuit system.

On the other hand, the digital broadcast receiver 12
In 1, so to convert the desired RF frequency channel signal once the up conversion circuit 126 to the 1st IF very high frequency such 1GHz, f _IN + 2f _IF
The image frequency f _IM becomes a considerably high frequency. Thus, the image signal will not be present on the other RF frequency channels and will not be a problem at this stage. However, when down-converting the first IF to the second IF having a lower frequency, the image signal is present in another frequency channel, as in the case of the single conversion type. Here, the other frequency channel is a frequency channel that is simultaneously up-converted when the desired RF frequency channel signal is up-converted to the first IF.

Since the frequency of the first IF is fixed as described above, the image frequency f _{IM at} the time of down-conversion to the second IF is inevitably constant.
The image trap formed here may be a fixed trap. Therefore, a high-performance trap is easily formed. Therefore, it can be said that the double conversion type is a circuit system having excellent image interference characteristics as compared with the single conversion type.

However, even if an image trap is used in the digital broadcast receiver 121 of the double conversion type, when obtaining the second IF, 45.75 MHz in the US system and 5 in the Japanese system, respectively.
Since the second IF is set to a low frequency such as 8.75 MHz, the frequency interval between the desired signal and the image signal becomes narrow, similarly to the case where the IF is obtained in the single conversion type digital broadcast receiver 101. . Therefore, it is very difficult to greatly attenuate only the image signal. In addition, since an image trap is required, there is a problem that the configuration of the receiver is complicated.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described conventional problems, and has as its object to provide a simple configuration capable of easily removing an image signal from a received digital broadcast signal and suppressing reception interference. To provide a digital broadcast receiver.

[0015]

According to a first aspect of the present invention, there is provided a digital broadcast receiver for converting a lower intermediate frequency from a desired signal selected from a digital broadcast signal. In a digital broadcasting receiver having a down-conversion circuit for generating, the down-conversion circuit is an image rejection type mixer for removing an image signal accompanying the desired signal.

According to the above invention, the intermediate frequency is generated while removing the image signal accompanying the desired signal by using the down-conversion circuit as an image rejection type mixer. Therefore, even when the frequency of the intermediate frequency in the down-converting circuit is relatively low and the frequency of the desired signal and the frequency of the image signal are not so far from each other, there is no possibility of receiving interference due to the image signal.

In addition, there is no need to provide an image signal removal trap circuit in the preceding stage of the down-conversion circuit, and the intermediate frequency (Low IF) of the lowest frequency generated by the two-stage down-conversion circuit as in the prior art is eliminated. , 1
Since the signal can be generated by the down-converting circuit of the stage, the receiving circuit can be simplified.

As a result, it is possible to provide a digital broadcast receiver having a simple configuration capable of easily removing an image signal from a received digital broadcast signal and suppressing reception interference.

According to a second aspect of the present invention, there is provided a digital broadcasting receiver for generating a higher intermediate frequency from the desired signal in the digital broadcasting receiver according to the first aspect. In addition, an up-conversion circuit for outputting to a subsequent circuit including the down-conversion circuit is provided.

According to the above invention, after the intermediate frequency of a higher frequency is once generated from the desired signal by the up-conversion circuit, the down-conversion circuit, that is, the image rejection type mixer, removes the image signal and lowers the lower frequency than the desired signal. Generate an intermediate frequency. Therefore, even when the frequency of the intermediate frequency in the down-converting circuit is relatively low and the frequency of the desired signal and the frequency of the image signal are not so far from each other, there is no possibility of receiving interference due to the image signal.

In addition, there is no need to provide an image signal removal trap circuit in the preceding stage of the down-conversion circuit, and as in the prior art, the intermediate frequency (the lowest frequency) generated by the two-stage down-conversion circuit after the up-conversion process. Low IF) can be generated by a one-stage down-conversion circuit, so that the reception circuit can be simplified.

As a result, it is possible to provide a double-conversion type digital broadcast receiver having a simple configuration capable of easily removing an image signal from a received digital broadcast signal and suppressing reception interference.

According to a third aspect of the present invention, there is provided a digital broadcast receiver according to the first or second aspect, wherein the down-converting circuit outputs an output from a local oscillator. And generating the intermediate frequency having a frequency that is a difference between the frequency of the oscillation signal to be input and the frequency of the desired signal input to the down-conversion circuit, and converting the image signal into the frequency of the image signal and the frequency of the oscillation signal. Is converted into a signal having a frequency of the sum of

According to the above invention, the down conversion circuit, that is, the image rejection type mixer is
When generating an intermediate frequency having a frequency that is the difference between the frequency of the oscillation signal output from the local oscillator and the frequency of the desired signal input to the down-conversion circuit, the image signal is converted into the image signal frequency and the oscillation signal frequency. To a signal having the frequency of the sum of Therefore, the frequency of the image signal is converted to a higher frequency by the frequency of the oscillation signal. As a result, the image signal is removed, and the converted signal has a frequency sufficiently distant from the desired signal, thereby facilitating the removal.

According to a fourth aspect of the present invention, there is provided a digital broadcast receiver according to the third aspect of the present invention, wherein the image signal of the image signal is provided downstream of the down-conversion circuit. A filter for removing a signal having a frequency equal to the sum of the frequency and the frequency of the oscillation signal is provided.

According to the above invention, the down-conversion circuit, that is, the signal corresponding to the image signal input to the image rejection type mixer and having the sum of the frequency of the image signal and the frequency of the oscillation signal is output. Is removed by a filter provided at the subsequent stage. As a result, the signal related to the image signal is completely removed, so that subsequent signal processing can be performed without leaving unnecessary frequency components.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] FIGS. 1 and 2 show an embodiment of a digital broadcast receiver according to the present invention.
This will be described below.

FIG. 1 shows a block diagram of a digital broadcast receiver 1 according to the present embodiment. The digital broadcast receiver 1 is a single conversion type receiver, and includes an antenna 2, a tuning circuit 3, a high frequency amplifier circuit 4, a frequency conversion circuit 5, and a low IF amplifier circuit 6. That is, a desired signal is selected by the tuning circuit 3 from the digital broadcast signal received by the antenna 2, the desired signal is amplified by the high frequency amplifier circuit 4, and the desired signal is low while removing the image signal by the frequency conversion circuit 5.
After the frequency conversion to the IF, the Low IF amplifier circuit 6 amplifies the Low IF to obtain a Low IF output.

The tuning circuit 3 comprises a tracking band-pass filter 3a capable of changing the center frequency in conjunction with the reception frequency. The tuning circuit 3 converts a digital broadcast signal input to the antenna 2 into a desired signal corresponding to the degree of selection. Take out.

The high-frequency amplifier circuit 4 comprises an RF amplifier 4a and a tracking bandpass filter 4b. The RF amplifier 4a amplifies the desired signal extracted by the tuning circuit 3 to a gain necessary for a subsequent circuit. The tracking bandpass filter 4b converts the desired signal amplified by the RF amplifier 4a into a signal from which unnecessary signals have been removed in accordance with the selectivity.

The frequency conversion circuit 5 comprises a local oscillator 5a and a down-conversion circuit 5b. Local oscillator 5a outputs an oscillation signal having a predetermined oscillation frequency f _LO to down-convert circuit 5b. Down conversion circuit 5
b denotes an image rejection type mixer to be described later, and a frequency f _D input through the high-frequency amplifier circuit 4.
_Is mixed with the oscillation signal of the oscillation frequency f _LO from the local oscillator 5a, so that the frequency f _IF =
It has a function of generating a low IF of f _LO −f _D (f _IF <f _D ) and removing an image signal having an image frequency f _IM having a relation of f _IF = f _IM −f _LO .

The low IF amplifier circuit 6 includes a band pass filter 6a and a low IF amplifier 6b. The bandpass filter 6a removes unnecessary components from the signal output from the frequency conversion circuit 5, and outputs a low IF signal.
The amplifier 6b amplifies the output of the band-pass filter 6a and makes it a Low IF output.

Next, the circuit configuration and operation of the image rejection type mixer constituting the down-convert circuit 5b will be described with reference to FIG. FIG.
As shown in the figure, the input signal A of the image rejection type mixer is obtained by converting the oscillation signal F from the local oscillator 5a by 90
The signal whose phase is shifted by 90 ° by the phase shifter 51 is multiplied by the multiplier 52 to generate a signal B. On the other hand, the input signal A is the oscillation signal F from the local oscillator 5a and the multiplier 5
The signal C is generated by multiplying by three. Signal C is 9
The phase is shifted by 90 ° by the 0 ° phase shifter 54 and the signal D
Then, the adder 55 adds the signal B to the output signal E to generate an output signal E.

[0034] In the above operation, (= 2πf _D ω _D) a desired signal (input signal A) sinω _D t, the local oscillator 5
When the oscillation signal F of a and _{sinω Lo t (ω Lo = 2πf} LO), each part of the signal is calculated as follows.

[0035] _{A: sinω D t B: sinω} D t × sin (ω Lo t-90 °) = (1/2) × cos (ω Lo t-90 ° -ω D t) + (1/2) × _{cos (ω Lo t-90 °} + ω D t) C: sinω D t × sinω Lo t = (1/2) × cos (ω Lo t-ω D t) + (1/2) × cos (ω Lo t + ω _D t) D: (１ ／) × cos (ω _Lo t−ω _D t−90 °) + (１ ／) × cos (ω _Lo t + ω _D t−90 °) E: B + D = cos (ω _{Lo t-ω D t-90 °} ) + cos (ω Lo t + ω D t-90 °) = sin (ω Lo t-ω D t) + sin (ω Lo t + ω D t) Thus, from the image rejection type mixer a frequency f _D of the desired signal (input signal a), the output signal E is output having a frequency difference and the sum of the oscillation frequency f _LO of the oscillator signal F of the local oscillator 5a . Low to get
IF has a difference frequency component sin (ω _Lot −ω
_D t), the sin (ω _Lot ) of the frequency of the sum component
+ Ω _D t) may be removed by the subsequent band-pass filter 6a.

On the other hand, as the input signal A, an image signal: s
The signal of each unit when inω _IM t (ω _IM = 2πf _IM ) is input is calculated as follows.

A: sin ω _IM t B: sin ω _IM t × sin (ω _Lo t−90 °) = (１ ／) × cos (ω _IM t−ω _Lot t + 90 °) + (×) × cos ( _{ω IM t + ω Lo t-} 90 °) C: sinω IM t × sinω Lo t = (1/2) × cos (ω IM t-ω Lo t) + (1/2) × cos (ω IM t + ω Lo t) D: (1/2) × cos (ω _IM t−ω _Lo t−90 °) + (１ ／) × cos (ω _IM t + ω _Lo t−90 °) E: B + D = cos (ω _IM t + ω _Lot ) −90 °) = sin (ω _IM t + ω _Lot ) Thus, the image frequency f _IM of the image signal (input signal A) is output from the image rejection type mixer.
And an output signal E having the sum of the oscillation frequency f _LO of the oscillation signal F of the local oscillator 5a. As a result, the image frequency f _IM is converted into the frequency f _IM + f _LO , and the image signal is removed. Further, the frequency f _IM + f
_{Since the LO} is farther away from the low IF frequency f _LO -f _D than the image frequency f _IM , the _LO can be easily removed by the subsequent band-pass filter 6a, and the band-pass filter 6a can remove the _LO from the band-pass filter 6a. No frequency component is output.

As described above, according to the digital broadcast receiver 1 of the present embodiment, even if an image signal is input to the image rejection type mixer constituting the down-conversion circuit 5b, it causes reception interference. It can be confirmed that the frequency component of the difference between the image frequency f _IM and the oscillation frequency f _LO of the local oscillator 5a is not output, and that the frequency component output in association with the image signal can be easily removed. That is, even if the image frequency f _IM input to the image rejection type mixer is not so far from the frequency f _{D of the} desired signal, no reception interference is caused. Therefore, it is not necessary to provide an image signal removal trap circuit in the preceding stage of the down-conversion circuit 5b, and the low IF generated by the two-stage down-conversion circuit is generated by the one-stage down-conversion circuit as in the related art. Therefore, the receiving circuit can be simplified.

[Embodiment 2] Another embodiment of the digital broadcast receiver of the present invention is described below with reference to FIG. For convenience of explanation, components having the same functions as those shown in the drawings of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 3 shows a block diagram of the digital broadcast receiver 11 of the present embodiment. Digital broadcast receiver 11
Is a double conversion type receiver, which comprises an antenna 12, a tuning circuit 13, a high frequency amplifier circuit 14, a first frequency converter circuit 15, a first IF amplifier circuit 16, a second frequency converter circuit 17, and a low IF amplifier circuit 18. Is done. That is, a desired signal is selected by the tuning circuit 13 from the digital broadcast signal received by the antenna 12, the desired signal is amplified by the high-frequency amplifier circuit 14, and then converted to the first IF by the first frequency conversion circuit 15 to be converted to the first IF. The signal is amplified by the amplifier circuit 16. Next, after the first IF is frequency-converted to a low IF while removing the image signal by the second frequency conversion circuit 17, the low IF amplifying circuit 18 converts the low IF to a low IF.
Is amplified to be a Low IF output.

The tuning circuit 13 is composed of a wideband band-pass filter 13a that passes only the frequency to be received, and selects a desired signal of the frequency to be received from the digital broadcast signal input to the antenna 12.

The high-frequency amplifier circuit 14 includes a broadband amplifier 14
a, and amplifies the desired signal selected by the tuning circuit 13 to a gain required for a subsequent circuit.

The first frequency conversion circuit 15 includes the local oscillator 1
5a and an up-conversion circuit 15b. Local oscillator 15a outputs an oscillation signal having a predetermined oscillation frequency to up-conversion circuit 15b. The up-conversion circuit 15b generates a 1st IF having a higher frequency than the desired signal by mixing the desired signal input through the high-frequency amplifier circuit 14 and the oscillation signal from the local oscillator 15a. Since the frequency of the first IF is fixed, the oscillating frequency of the local oscillator 15a is set to be variable,
The frequency is set to

The first IF amplifying circuit 16 comprises a band pass filter 16a, a first IF amplifier 16b, and a band pass filter 16c. The band-pass filter 16a removes unnecessary frequency components from the signal output from the first frequency conversion circuit 15, and outputs the output
The signal is amplified by the IF amplifier 16b. Then, the band of the amplified signal is limited by the band-pass filter 16c according to the selectivity.

The second frequency conversion circuit 17 includes the local oscillator 1
7a and a down-conversion circuit 17b. Local oscillator 17a outputs an oscillation signal having a predetermined oscillation frequency f _LO to down-convert circuit 17b. The down-conversion circuit 17b is composed of the image rejection type mixer described in the first embodiment, and includes a first IF
And desired signal of a frequency f _D which is input through the amplifier circuit 16, an oscillation signal and frequency by mixing the f _IF = f _LO -f _D from the local oscillator 17a (f _IF <f _D)
And a low IF of f _IF = f _IM −f _LO
Has a function of removing an image signal having an image frequency f _{IM satisfying} the following relationship.

The low IF amplifier 18 includes a band pass filter 18a and a low IF amplifier 18b. The band-pass filter 18a removes unnecessary components from the signal output from the second frequency conversion circuit 17, and the low IF amplifier 18b uses the band-pass filter 1
The output of 8a is amplified to be a Low IF output.

Since the circuit configuration and operation of the image rejection type mixer are the same as those in the first embodiment, the description is omitted.

As described above, according to the digital broadcast receiver 11 of the present embodiment, the down conversion circuit 17b
Even if an image signal is input to the image rejection type mixer, the frequency component of the difference between the image frequency f _IM causing reception interference and the oscillation frequency f _LO of the local oscillator 17a is not output, and It can be confirmed that the frequency component output in association with the signal can be easily removed. That is, even if the image frequency f _IM input to the image rejection type mixer is not so far from the frequency f _{D of the} desired signal, no reception interference is caused. Therefore, the down conversion circuit 1
There is no need to provide an image signal removal trap circuit in the preceding stage of 7b, and L generated by a two-stage down-converting circuit after up-conversion processing as in the related art.
Since the ow IF can be generated by a one-stage down-conversion circuit, the receiving circuit can be simplified.

[0049]

As described above, the digital broadcast receiver according to the first aspect of the present invention has the down-convert circuit for generating a lower intermediate frequency from the desired signal selected from the digital broadcast signal. In the digital broadcast receiver, the down-conversion circuit is configured as an image rejection type mixer for removing an image signal accompanying the desired signal.

Therefore, even when the frequency of the intermediate frequency in the down-converting circuit is relatively low and the frequency of the desired signal is not so far from the frequency of the image signal,
There is no reception interference due to the image signal.

Further, it is not necessary to provide a trap circuit for removing an image signal in a stage preceding the down-conversion circuit, and the intermediate frequency (Low IF) of the lowest frequency generated by the two-stage down-conversion circuit as in the related art is not required. , 1
Since the signal can be generated by the down-converting circuit of the stage, the receiving circuit can be simplified.

As a result, it is possible to provide a digital broadcast receiver having a simple configuration capable of easily removing an image signal from a received digital broadcast signal and suppressing reception interference.

According to the digital broadcasting receiver of the second aspect of the present invention, as described above, in the digital broadcasting receiver of the first aspect, a higher intermediate frequency is generated from the desired signal. This is a configuration having an up-convert circuit for outputting to a subsequent circuit including the down-convert circuit.

Therefore, even when the frequency of the intermediate frequency in the down-converting circuit is relatively low and the frequency of the desired signal and the frequency of the image signal are not so far from each other,
There is no reception interference due to the image signal.

Further, it is not necessary to provide a trap circuit for removing an image signal before the down-conversion circuit, and unlike the prior art, the intermediate frequency (the lowest frequency) generated by the two-stage down-conversion circuit after the up-conversion processing. Low IF) can be generated by a one-stage down-conversion circuit, so that the reception circuit can be simplified.

As a result, it is possible to provide a double-conversion type digital broadcasting receiver having a simple configuration capable of easily removing an image signal from a received digital broadcasting signal and suppressing reception disturbance. Play.

According to a third aspect of the present invention, as described above, in the digital broadcast receiver according to the first or second aspect, the down-converting circuit includes an oscillator output from a local oscillator. Generating an intermediate frequency having a frequency that is a difference between the frequency of the signal and the frequency of the desired signal input to the down-converting circuit, and converting the image signal into a sum of the frequency of the image signal and the frequency of the oscillation signal; Is converted into a signal having a frequency of

Therefore, the frequency of the image signal is converted to a higher frequency by the frequency of the oscillation signal.
As a result, the image signal is removed, and the converted signal has a frequency sufficiently distant from the desired signal, so that the removal is facilitated.

According to a fourth aspect of the present invention, there is provided a digital broadcasting receiver according to the third aspect of the present invention, wherein:
A configuration is provided that includes a filter that removes a signal having a frequency that is the sum of the frequency of the image signal and the frequency of the oscillation signal.

Therefore, since the signal related to the image signal is completely removed, there is an effect that subsequent signal processing can be performed without leaving unnecessary frequency components.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital broadcast receiver according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an image rejection type mixer used in the digital broadcast receiver of FIG. 1;

FIG. 3 is a block diagram showing a configuration of a digital broadcast receiver according to another embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional digital broadcast receiver.

FIG. 5 is a block diagram showing a configuration of another conventional digital broadcast receiver.

FIG. 6 is an explanatory diagram illustrating a frequency distribution of a signal related to reception of a digital broadcast signal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Digital broadcasting receiver 3 Tuning circuit 3a Tracking bandpass filter 4 High frequency amplifier circuit 4a RF amplifier 4b Tracking bandpass filter 5 Frequency conversion circuit 5a Local oscillator 5b Down conversion circuit (image rejection type mixer) 6 Low IF amplifier circuit 6b Low IF amplifier 13 Tuning circuit 14 High-frequency amplifier circuit 15 First frequency conversion circuit 15a Local oscillator 15b Up-conversion circuit 16 1st IF amplifier circuit 17 Second frequency conversion circuit 17a Local oscillator 17b Down-conversion circuit (image rejection type mixer) 18 Low IF amplifier circuit 18b Low IF amplifier 51 90 ° phase shifter 52 Multiplier 53 Multiplier 54 90 ° phase shifter 55 Adder f _D frequency f _IM image frequency f _LO oscillation frequency

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K020 AA02 DD02 DD11 EE01 EE04 EE05 FF05 HH13 5K052 AA01 BB03 CC06 DD04 FF06 GG26

Claims (4)

[Claims] 1. A digital broadcast receiver having a down-converting circuit for generating a lower intermediate frequency from a desired signal selected from a digital broadcast signal, wherein the down-converting circuit is attached to the desired signal. A digital broadcast receiver characterized by being an image rejection type mixer for removing an image signal. 2. The digital broadcast according to claim 1, further comprising an up-conversion circuit for generating a higher intermediate frequency from the desired signal and outputting the intermediate frequency to a subsequent circuit including the down-conversion circuit. For receiver. 3. The down-conversion circuit generates the intermediate frequency having a frequency that is a difference between the frequency of an oscillation signal output from a local oscillator and the frequency of the desired signal input to the down-conversion circuit. The digital broadcast receiver according to claim 1, wherein the image signal is converted into a signal having a sum of a frequency of the image signal and a frequency of the oscillation signal. 4. A digital filter according to claim 3, further comprising a filter provided at a stage subsequent to said down-converting circuit, for removing a signal having a sum of the frequency of said image signal and the frequency of said oscillation signal. Broadcast receiver.