JP2000092021A - Digital broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the circuit constitution of a digital broadcast receiver by making it into an IC by using a digital filter instead of a low-pass filter. SOLUTION: By using tracking band-pass filters 2 and 4 and an amplifier 3 the frequency band of a desired channel is selected from high frequency signals inputted from an input terminal 1, the output is converted into IF signals in a mixer 5 and then, I signals and Q signals are generated through the mixer 9 and the mixer 10 respectively. By passing the I signals and the Q signals through the digital filters 13 and 14 for analog signals, signals other than the I and Q signals such as the frequency of an adjacent channel for becoming noise at the time of reproduction and obstructing the reproduction are excluded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a compressed image,
Voice and data are OFDM (Orthogonal Frequency D)
ivision Multiplexing (QAM) and Quadrature Amp
The present invention relates to a digital broadcast receiver for receiving a broadcast transmitted by a digital modulation method such as a litude modulation method.

[0002]

2. Description of the Related Art FIGS. 5 and 6 are block diagrams showing the configuration of a conventionally used digital broadcast receiver. FIG.
The digital broadcast receiver shown in FIG.

The conventional digital broadcast receiver shown in FIG.
Input terminal 1 and tracking bandpass filters 2 and 4
And amplifiers 3, 7, 19 and 23, mixers 5 and 21,
Local oscillators 6, 22, SAW filters 8, 20, low-pass filter 24 for band limitation, and AD converter 25
And an OFDM demodulator 18.

In the digital broadcast receiver having such a configuration, the tracking band pass filter 2 allows the RF signals in the VHF and UHF bands input from the input terminal 1 to be input.
Among the signals, an RF signal in the vicinity of the frequency band of the desired digital channel is obtained, and the obtained RF signal is amplified by the amplifier 3. RF amplified by the amplifier 3
The signal is filtered by the tracking bandpass filter 4 having a higher selectivity than the tracking bandpass filter 2 so that the RF signal near the frequency of the desired digital channel is obtained.
The signal is obtained as a narrower frequency band RF signal.

[0005] The RF signal obtained by the tracking bandpass filter 4 and the oscillation signal oscillated from the local oscillator 6 are input to a mixer 5, and the RF signal is mixed by mixing the two. 36.
The signal is converted to a first IF signal having a low frequency such as a 12 MHz band. The first IF signal is amplified by the amplifier 7 and further passed through SAW filters 8 and 20 to remove unnecessary components. By passing through the two-stage SAW filters 8 and 20 in this manner, a desired channel is extracted from the first IF signal.

The output signal of the SAW filter 20 from which a desired channel has been extracted as described above is input to a mixer 21 and mixed with an oscillation signal oscillated by a local oscillator 22, for example, in a 4.57 MHz band. The signal is converted to a second IF signal having a lower frequency. The second IF signal thus converted is amplified by the amplifier 23, and then band-limited by the low-pass filter 24 functioning as an anti-alias filter (filter for removing aliasing noise) of the AD converter 25 at the subsequent stage. The signal band-limited by the low-pass filter 24 is converted into a digital signal by the AD converter 25 and output to the OFDM demodulator 18.

Referring to FIGS. 3 and 4, the reason for using two stages of the SAW filter as described above will be described below. FIG. 3 shows an example of a European broadcast as an arrangement of channels to be received. FIG. 4 shows the spectrum of the received signal before and after frequency conversion by the mixer 21.

In FIG. 3, in the current analog broadcasting,
Channels are arranged every other channel in consideration of adjacent channel interference of the receiver. In digital broadcasting, such channels are arranged in such vacant channels of the current analog broadcasting, so that there is a high possibility that the analog channels are adjacent as shown in FIG. Also, digital broadcasting should not interfere with adjacent analog broadcasting,
It is transmitted at a level whose output level is lower by about 30 dB at maximum than that of an adjacent analog broadcast. for that reason,
In receiving a digital broadcast, it is necessary to consider the influence of the adjacent analog broadcast. Therefore, a filter for filtering an analog broadcast as described above requires a steep filter characteristic.

However, a SAW filter having a currently available pass frequency band of 8 MHz has a filter characteristic whose frequency corresponding to the peak of the level of the adjacent analog channel is 30 d with respect to the pass band frequency.
Only about B attenuation is obtained. As described above, the peak of the level of the adjacent analog channel is higher than that of the digital channel by about 30 dB.
Even if one filter is used, at the frequency corresponding to the peak of the level of the adjacent analog channel, the signal is input at the same level as the level of the digital channel. Therefore, in the conventional digital broadcast receiver, the above SA
By using two W filters, the attenuation of adjacent analog channels was obtained.

When the frequency conversion is performed by the mixer 21, the frequency difference between the local oscillation signal frequency FLo oscillated by the local oscillator 22 and the desired frequency FD is obtained in the analog channel, as shown in FIG. An image frequency F equal to the frequency difference from the local oscillation signal frequency FLo.
im. Therefore, when the frequency is converted by the mixer 21, the spectrum of the desired digital channel overlaps with the spectrum of the desired analog channel as shown in FIG. 4B. Therefore, such adjacent channel interference cannot be removed by the filter at the subsequent stage of the mixer 21, and must be removed at the preceding stage of the mixer 21. Therefore, the SAW filters 8 and 20 and the amplifier 19
Is inserted before the mixer 21. The SAW filters 8 and 20 inserted in this way have the function of removing interference of a normal adjacent analog channel and the function of the mixer 2.
1 also serves to eliminate image disturbance.

The digital broadcast receiver shown in FIG. 6 will be described. The conventional digital broadcast receiver shown in FIG. 6 has an input terminal 1 and tracking bandpass filters 2 and 4.
, Amplifiers 3, 7, mixers 5, 9, 10, local oscillators 6, 12, SAW filter 8, 90 ° phase shifter 11
, Low-pass filters 26 and 27, and AD converters 16,
17 and an OFDM demodulator 18.

In the digital broadcast receiver having such a configuration, as in the digital broadcast receiver of FIG. 5, of the RF signals input at the input terminal 1, an RF signal in the vicinity of the frequency band of a desired digital channel is used as a tracking bandpass. The RF signal obtained by the filters 2, 4 and the amplifier 3 is further mixed with an oscillated signal oscillated from the local oscillator 6 by the mixer 5 to convert the RF signal into a low-frequency IF signal. .

The IF signal thus converted is amplified by an amplifier 7 and input to a SAW filter 8. In the SAW filter 8, the signal level of an analog channel adjacent to a desired digital channel is attenuated. The mixer 9 generates an I signal by mixing the output of the SAW filter 8 with an oscillation signal having the same frequency as the IF signal output from the local oscillator 12. Further, the mixer 10 mixes the output of the SAW filter 8 and the phase of the oscillation signal output from the local oscillator 12 with the oscillation signal shifted by 90 ° by the 90 ° phase shifter 11 so as to convert the Q signal. Generate.

The I and Q signals generated as described above are input to low-pass filters 26 and 27 disposed after the mixers 9 and 10, respectively. Outputs of the low-pass filters 26 and 27 are respectively converted to AD converters 16 and 1
In 7, the digital signal is converted into a digital signal, and the converted digital signal is input to the OFDM demodulator 18.

At this time, the low-pass filters 26 and 27
Has two roles: Its role is (1) the role of the AD converters 16 and 17 at the subsequent stage as an anti-alias filter, and (2) the analog channel adjacent to the desired digital channel included in the I and Q signals is removed. Role. Regarding the latter role, when the signal level of the adjacent analog channel is large and very close to the desired digital channel, the low-pass filters 26 and 27 are required to have steep filter characteristics.

[0016]

In the digital broadcast receiver shown in FIG. 5, as two SAW filters such as SAW filters 8 and 20 are used, when the signals pass through the SAW filters 8 and 20, Two amplifiers, such as the amplifiers 7 and 19, are required to compensate for the passing loss that occurs. Therefore, miniaturization of the digital broadcast receiver has been prevented, and cost and power consumption have been disadvantageous.

Further, in the digital broadcast receiver shown in FIG. 6, the second IF like the digital broadcast receiver shown in FIG.
Since the signal is not converted to a low-frequency signal such as a signal, the image interference caused by the image frequency generated with the signal is eliminated and the use of the SAW filter is reduced, but the problem of adjacent analog channel interference remains. In order to prevent such interference, low-pass filters 26 and 27 each having a filter characteristic for removing adjacent analog channels included in the I and Q signals and including a coil and a capacitor are provided.

However, in order for the low-pass filters 26 and 27 to obtain desired filter characteristics, since the coils and capacitors constituting the low-pass filters 26 and 27 have individual variations, the coils are not used in the production process. And adjustment of the capacitor is required.

An object of the present invention is to reduce the number of SAW filters to be used, simplify a circuit constituting a digital broadcast receiver, and reduce the size of the digital broadcast receiver.

The present invention relates to the low-pass filters 26, 2
By using a digital filter in place of the filter 7, the filter characteristics can be changed by simpler means as compared with the low-pass filters 26 and 27 which change the filter characteristics by changing the coils and capacitors. It is an object of the present invention to provide a digital broadcast receiver capable of changing the digital broadcast receiver.

The present invention relates to the low-pass filters 26, 2
An object of the present invention is to simplify a circuit configuration of a digital broadcast receiver by forming an IC using a digital filter instead of the digital filter 7.

[0022]

A digital broadcasting receiver according to the first aspect of the present invention comprises: a signal conversion unit for converting a quadrature amplitude modulated digital RF signal using an I signal and a Q signal into an IF signal; I signal generating means for generating an I signal by mixing the IF signal with an oscillation signal having the same frequency as the IF signal; and generating a Q signal by mixing the IF signal with an oscillation signal having the same frequency as the IF signal. An input / output signal that is operated by a Q signal generating means and a clock signal output from a local oscillator, is connected to a stage subsequent to the I signal generating means and the Q signal generating means, and passes the I signal component and the Q signal component. And a digital filter for an analog signal using an analog signal.

In the digital broadcast receiver having such a configuration, by changing the frequency of the clock signal output from the local oscillator, the filter characteristic of the digital filter for the analog signal is changed to change the I signal component and the I signal component. And the Q signal component.

A digital broadcast receiver according to claim 2 is
I signal generating means for generating an I signal by mixing a digital RF signal subjected to quadrature amplitude modulation using an I signal and a Q signal with an oscillation signal having the same frequency as the RF signal;
The signal is mixed with an oscillation signal having the same frequency as that of the RF signal, and Q
A Q signal generating means for generating a signal, and a clock signal output from a local oscillator, and connected to a subsequent stage of the I signal generating means and the Q signal generating means;
A digital filter for an analog signal using an analog signal as an input / output signal for passing the signal component and the Q signal component.

In the digital broadcast receiver having such a configuration, the I signal generating means and the Q signal generating means directly orthogonally demodulate the RF signal, and then change the frequency of the clock signal output from the local oscillator. Thereby, the filter characteristic of the digital filter for the analog signal is changed to pass the I signal component and the Q signal component.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram illustrating the configuration of the digital broadcast receiver according to the first embodiment. 6, the same components as those of the conventional digital broadcast receiver in FIG. 6 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 7 is a block diagram showing the internal configuration of digital filters 13 and 14 for analog signals.

The digital broadcast receiver used in this embodiment is a digital filter for an analog signal to which a clock signal is input from a local oscillator 15 instead of the low-pass filters 26 and 27 in the conventional digital broadcast receiver shown in FIG. The analog signals output from the digital filters 13 and 14 for analog signals are input to AD converters 16 and 17 using the analog signal converters 13 and 14, respectively.

In the digital broadcast receiver having such a configuration, as in the conventional digital broadcast receiver of FIG. 6, of the RF signals input at the input terminal 1, an RF signal near the frequency band of a desired digital channel is tracked. The RF signal obtained by the band-pass filters 2 and 4 and the amplifier 3 is further mixed with an oscillating signal oscillated from a local oscillator 6 by the mixer 5 to the obtained RF signal.
The F signal is converted to a low frequency IF signal.

After the IF signal thus converted passes through the amplifier 7 and the SAW filter 8, the SA signal is
The output of the W filter 8 is combined with the oscillation signals output from the local oscillator 12 and the 90 ° phase shifter 11 and the mixers 9 and 9 respectively.
By mixing at 10, an I signal and a Q signal are generated, and the I and Q signals are input to digital filters 13 and 14 for analog signals, respectively. The digital filters 13 and 14 for analog signals use digital signals as coefficients, can perform analog-to-digital multiplication, and operate by a clock signal generated from a local oscillator 15.

The digital filters 13 and 14 for analog signals to which the I and Q signals are input include a clock input terminal 28 to which a clock signal is input from the local oscillation circuit 15 and an output of the mixer 9 as shown in FIG. Alternatively, an analog signal input terminal 29 to which an output of the mixer 10 is input, hold circuits (delay circuits) 30 to 33 for delaying respective input signals by a period of a clock signal, and the hold circuits 30 to 33
Multiplier 3 for multiplying each of the signal passed through 33 and the signal input to analog signal input terminal 29 by a certain coefficient
4 to 38; an adder 39 for adding all outputs from the multipliers 34 to 38; and an analog signal output terminal 48 for outputting an output from the adder 39.

A digital filter for an analog signal will be described with reference to FIG. FIG. 8 shows a digital filter for an analog signal to be a two-element filter. The analog signal digital filter 40 includes a clock input terminal 41 to which a clock signal is input, and an input signal X.
(T) is input, an analog signal input terminal 42, a hold circuit (delay circuit) 43 for delaying by the cycle T of the clock signal, and the input signal X (t) and the output X (t−T ), Multipliers 44 and 45 for multiplying by coefficients α and β, an adder 46 for adding the outputs of the multipliers 44 and 45, and an output signal Y from the adder 46.
An analog signal output terminal 47 for outputting (t) is provided.

The output signal Y (t) output from the analog signal output terminal 47 of the digital filter 40 for analog signals is Y (t) = αX (t) + βX (t−
T). For simplicity, input signal X (t) = cosω
t, α = β = 1, the output signal is Y (t) = 1 × c
osωt + 1 × cosω (t−T). Further, this output signal is Y (t) = 2cos (ωT / 2) · cosω
(T−T / 2). When ωT = (2n + 1) π,
cos (ωT / 2) = 0 and the output signal Y (t) is always 0, whereas when ωT = 2nπ, |
cos (ωT / 2) | = 1, and the output signal Y (t) is not attenuated.

When the frequency of the input signal X (t) is f, ω = 2πf. Now, when an input signal X (t) having a frequency f such that f = (2n + 1) / T is input to the analog signal digital filter 40, an output signal Y
(T) is always 0, and there is no output from the digital filter 40 for analog signals. Further, when an input signal X (t) having a frequency f where f = 2n / T is input, the level of the output signal Y (t) is changed to an input signal X of another frequency.
This is the maximum level as compared with the case where (t) is input. In this way, by changing the output level according to the frequency, the digital filter 40 for the analog signal is changed.
Are separated into signals having frequencies that can pass through and signals having frequencies that cannot pass. At this time, it is clear from the above equation that the passable frequency and the non-passable frequency can be changed by the cycle T of the clock signal.

A logic element having such a configuration as a digital filter 40 for an analog signal, which is a two-element filter, which is stacked in several stages as shown in FIG. 7, is a digital signal for an analog signal employed in the present embodiment. Filters 13 and 14. Digital filters 13 and 14 for the analog signals
Performs the same operation as the operation of the digital filter 40 for analog signals.

That is, first, the hold circuits 30 to 33
, The input signal X (t) input to the analog signal input terminal 29 is delayed by the period T of the clock signal input to the clock input terminal 28 from the local oscillation circuit 15. Then, in the multipliers 34 to 38, the input signal X (t) and the signals X (t−T), X (t−2T),
X (t−3T),..., X (t−nT) are coefficients α0, α
1, α2, α3,..., Αn.
Are all added by the adder 39. At this time, the coefficient α
0 to αn are determined to be appropriate values to give filter characteristics as low-pass filters to the digital filters 13 and 14 for analog signals, and at the same time, the period T of the clock signal.
Is changed, and only the desired I and Q signals can pass and a sharp filter characteristic is provided.

As described above, when the digital filters 13 and 14 for analog signals are set to operate as low-pass filters through which I and Q signals pass, I and Q
A signal such as an analog channel adjacent to a desired digital channel other than the signal is removed, and the AD converter 1 at the subsequent stage is removed.
Serves as 6,17 anti-alias filter. Thus, the digital filters 13 and 14 for analog signals are used.
I and Q signals passing through the A / D converters 16 and 1
7, and is converted into a digital signal.
The signal is input to the FDM demodulator 18.

The second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram illustrating a configuration of a digital broadcast receiver according to the second embodiment.

The digital broadcast receiver used in the present embodiment shown in FIG. 2 has an input terminal 1, tracking bandpass filters 2, 4, an amplifier 3, mixers 9, 10, a local oscillator 12, a 90.degree. Phase shifter 11, digital filters 13 and 14 for analog signals, and AD converters 16 and 1
7 and an OFDM demodulator 18.

In the digital broadcast receiver having such a configuration, like the digital broadcast receiver used in the first embodiment, of the RF signals input at the input terminal 1, the RF signal near the frequency band of the desired digital channel is selected. A signal is acquired by the tracking bandpass filters 2 and 4 and the amplifier 3.

The RF signal output in this manner is input to mixers 9 and 10. The mixer 9 includes the R
An I signal is generated by mixing the F signal with an oscillation signal having the same frequency as the RF signal output from the local oscillator 12. Further, the mixer 10 includes the RF signal,
The phase of the oscillation signal output from the local oscillator 12 is set to 9
The Q signal is generated by mixing with the oscillation signal shifted by 90 ° by the 0 ° phase shifter 11. Then, the I and Q signals are input to digital filters 13 and 14 for analog signals, respectively. The digital filters 13 and 14 for analog signals use digital signals as coefficients, can perform analog-to-digital multiplication, and operate by a clock signal generated from a local oscillator 15.

The digital filter 13 for analog signals,
14 uses a digital filter for an analog signal as shown in FIG. 7 similar to the first embodiment. As in the first embodiment, the local oscillators 15 and 14 are configured so that the digital filters 13 and 14 for analog signals having such a configuration operate as low-pass filters through which I and Q signals pass.
When the period of the clock signal oscillated from is set, I,
Signals other than the Q signal, such as analog channels adjacent to the desired digital channel, are removed, and work as anti-alias filters for the AD converters 16 and 17 at the subsequent stage. As described above, the digital filters 13 and 1 for the analog signal are used.
4 are passed through the AD converters 16,
17 and is converted into a digital signal,
The signal is input to the OFDM demodulator 18.

As described above, when demodulating the I and Q signals, the quadrature demodulation for directly converting the RF signal into the I and Q signals is performed, so that the I and Q signals used in the first embodiment are used.
In the present embodiment, the mixer 5, the local oscillator 6, the amplifier 7, and the SAW filter 8 for converting into an F signal can be eliminated.

[0043]

According to the digital broadcast receiver of claim 1, an I signal is generated by mixing an IF signal and an oscillation signal of a local oscillator having the same frequency as the IF signal, and the phase of the oscillation signal is set to 90%. The phase-shifted oscillation signal was mixed with the IF signal to generate a Q signal. Since the IF signal is subjected to the quadrature demodulation, the SAW filter and the amplifier that compensates for the attenuation by the SAW filter can be reduced or eliminated, and the circuit can be simplified.

Further, since a digital filter for an analog signal which operates with a clock signal and uses an analog signal as an input / output signal is used as a low-pass filter, the clock signal input to the digital filter for the analog signal is changed. This makes it possible to change the filter characteristics, thereby easily removing adjacent analog channels and easily functioning as an anti-alias filter of the AD converter at the subsequent stage. Also, by using such a digital filter for analog signals,
The circuit can be integrated into an IC.

A digital broadcast receiver according to claim 2 generates an I signal obtained by mixing an RF signal and an oscillation signal of a local oscillator having the same frequency as the RF signal, and shifts the phase of the oscillation signal by 90 °. The phased oscillation signal was mixed with the RF signal to generate a Q signal. As described above, since the RF signal is directly quadrature-demodulated, the SAW filter and the amplifier that compensates for the attenuation by the SAW filter can be further reduced or eliminated, and the circuit can be simplified.

Further, since a digital filter for an analog signal which operates with a clock signal and uses an analog signal as an input / output signal is used as a low-pass filter, the clock signal input to the digital filter for the analog signal is changed. This makes it possible to change the filter characteristics, thereby easily removing adjacent analog channels and easily functioning as an anti-alias filter of the AD converter at the subsequent stage. Also, by using such a digital filter for analog signals,
The circuit can be integrated into an IC.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a configuration of a digital broadcast receiver according to a second embodiment of the present invention.

FIG. 3 is a spectrum diagram in a mixed analog and digital broadcast.

FIG. 4 is a spectrum diagram before and after frequency conversion in digital broadcast reception.

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

FIG. 6 is a block diagram showing another example of the configuration of a conventional digital broadcast receiver.

FIG. 7 is a block diagram showing a circuit configuration of a digital filter for an analog signal shown in FIGS. 1 and 2;

FIG. 8 is a block diagram showing a circuit configuration of a digital filter for an analog signal which is a two-element filter.

[Explanation of symbols]

 Reference Signs List 1 high-frequency input terminal 2 tracking bandpass filter 3 amplifier 4 tracking bandpass filter 5 mixer 6 local oscillator 7 amplifier 8 SAW filter 9, 10 mixer 11 90 ° phase shifter 12 local oscillator 13, 14 digital filter for analog signal 15 local Oscillator 16, 17 AD converter 18 OFDM demodulator 19 Amplifier 20 SAW filter 21 Mixer 22 Local oscillator 23 Amplifier 24 Low-pass filter 25 AD converter 26, 27 Low-pass filter 28 Clock input terminal 29 Analog signal input terminal 30-33 Hold circuit 34 -38 Multiplier 39 Adder 40 Digital filter for analog signal 41 Clock input terminal 42 Analog signal input terminal 43 Hold circuit 44,45 Multiplier 46 Adder 47,48 Grayed signal output terminal

Claims (2)

[Claims] 1. A signal conversion means for converting a digital RF signal subjected to quadrature amplitude modulation using an I signal and a Q signal into an IF signal, and mixing the IF signal with an oscillation signal having the same frequency as the IF signal. I signal generating means for generating an I signal by using a clock signal output from a local oscillator, and Q signal generating means for generating an Q signal by mixing the IF signal with an oscillation signal having the same frequency as the IF signal. And a digital filter for an analog signal which is connected to the subsequent stage of the I signal generating means and the Q signal generating means and uses an analog signal as an input / output signal for passing the I signal component and the Q signal component. A digital broadcast receiver characterized by the following. 2. I signal generating means for generating an I signal by mixing an oscillation signal having the same frequency as the RF signal with a quadrature amplitude modulated digital RF signal using an I signal and a Q signal; A Q signal generating means for generating a Q signal by mixing the signal with an oscillation signal having the same frequency as the RF signal; an I signal generating means and the Q signal generating means operating with a clock signal output from a local oscillator; And a digital filter for an analog signal that uses an analog signal as an input / output signal for passing an I signal component and a Q signal component.