JP3538054B2 - Digital broadcast receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a DAB (Dig)
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcast receiver for receiving a digital broadcast signal such as ital Audio Broadcasting, and more particularly, to a digital broadcast receiver equipped with an improved AGC.

[0002]

2. Description of the Related Art Digital broadcast signals such as DAB are transmitted in units of a transmission frame including a digitally modulated carrier part (data part) and a null part having no carrier, and are used as a front end of a receiver. Indicates that digital broadcasting is an input signal. AG
In a receiver with a built-in C, it is necessary to increase the AGC response time with respect to the null time width in consideration of the purpose of synchronizing the null portion at the time of demodulation. Also, the time width Ts of the synchronization signal
The width differs depending on the transmission mode. In a conventional digital broadcast receiver that receives digital broadcast signals in a plurality of transmission modes, the response time of the AGC is fixed, so that the time width of the synchronization signal is fixed. The AGC response time is adjusted to the time width Ts of the synchronization signal in the transmission mode having the longest Ts.

[0003]

The AGC must operate sensitively to the variation in the electric field strength of the received signal due to fading. However, in the conventional digital broadcast receiver, the response time of the AGC is low. Since the time width Ts of the synchronization signal of the transmission frame is adjusted to the maximum transfer mode, the responsiveness is deteriorated when receiving a digital broadcast signal in the transmission mode with the time width Ts of the synchronization signal or a short transmission mode.

An object of the present invention is to provide a digital broadcast receiver which overcomes the above-mentioned problems.

[0005]

According to the digital broadcast receiver (10, 40) of the present invention, the transmission frame has a synchronization signal consisting of a continuous sequence of a plurality of nulls at the beginning, and the transmission frame is a unit. The AGC is performed so that the input level to the demodulator (33, 76) becomes substantially a predetermined level regardless of the electric field strength of the digital broadcast signal with respect to the selected digital broadcast signal. The digital broadcast signals can be received in a plurality of transmission modes in which the time width Ts of the synchronization signal differs depending on the transmission mode. The digital broadcast receiver (10, 40) detects the time width Ts of the synchronization signal of the currently selected digital broadcast signal,
The AGC response time is controlled in accordance with the detection time width Ts so as to be as short as possible and longer than the detection time width Ts.

The digital broadcast receiver (10, 40) includes not only a radio digital broadcast signal but also a television digital broadcast signal. Digital broadcast receiver (1
0,40) especially includes a DAB car radio (10,40).

Thus, a digital broadcast receiver (10, 40)
The response time of the AGC is variable and is set to the minimum value while ensuring the detection of the synchronization signal with respect to the digital broadcast signal in each transmission mode.
A good AGC function can be achieved even when receiving a digital broadcast signal having a short synchronization signal time width Ts. In addition,
The AGC response time is controlled by the RF stage (11, 41) and the IF stage.
(12, 42), the AGC response time is determined by the time width T of the synchronization signal.
Even if the digital broadcast receiver (10, 40) is fixed so as to conform to the largest one, the digital broadcast receiver (10, 40) and the digital broadcast receiver Included in the technical scope of (10,40).

A digital broadcast receiver according to the present invention (10, 40)
According to the control of the response time of the AGC, the RF stage (11, 41)
And in both the IF stage (12,42).

The AGC response times in the RF stage (11, 41) and the IF stage (12, 42) may be the same or different. If different, the RF stage (11, 41) and the IF stage (1
Of the AGCs of 2,42), the response time of the priority is shortened.

A digital broadcast receiver according to the present invention (10, 40)
According to the control of the AGC response time, the AGC signal generation unit (21, 29, 53, 62, 71) and the gain control unit (18, 27, 47, 49, 60, 69)
By controlling the time constant τ of the integrators (22, 30, 54, 63, 72) interposed between them.

The gain of the gain control unit (18, 27, 47, 49, 60, 69) includes both the amplification factor and the attenuation factor, and the gain control unit (18, 2
7, 47, 49, 60, 69) may be an amplifier or an attenuator.

By controlling the time constant τ of the integrators (22, 30, 54, 63, 72), the response of the AGC to the level change of the demodulated signal within the time width Ts of the synchronization signal of the transmission frame is sufficiently suppressed. can do. Although the time constants τ of the integrators (22, 30, 54, 63, 72) are generally the same, different values may be given to priorities for AGC control at each location.

A digital broadcast receiver according to the present invention (10, 40)
According to the method, the detection of the time width Ts of the synchronization signal of the digital broadcasting signal being selected is detected from the output of the demodulator (33, 76).

Since the transmission frame of the digital broadcast signal is restored by the demodulator (33, 76), the time width Ts of the synchronization signal of the transmission frame can be easily detected from the output of the demodulator (33, 76). .

[0015]

Embodiments of the present invention will be described below with reference to the drawings. Figure 1 shows a DAB car radio 10
It is a principal part block diagram of. DAB car radio 10
RF stage as front end in order from signal flow
11, a demodulation stage including an IF stage 12 and a demodulator 33 is provided. In the RF stage 11, the antenna 15 generates an RF signal of a predetermined level or more from all digital radio broadcast radio waves whose current location of the DAB car radio 10 is a service area, and outputs the RF signals of all these digital radio broadcasts.
After passing the signal through the RF stage broadband filter 16, the signal
The signal is amplified in the F-stage amplifier 17 and is amplified in the RF-stage attenuator 18.
Is attenuated. Local oscillator 20 generates a signal at an oscillating frequency related to the ensemble RF signal containing the service selected by the user, and mixer 19 multiplies the input signal from RF stage attenuator 18 by the input signal from local oscillator 20. As a result, an IF signal is generated. RF stage A
The GC detection circuit 21 detects an output level of the mixer 19 and outputs a control signal to the mixer 19 for maintaining the output level at a predetermined level. The integrator 22 integrates the output of the RF stage AGC detection circuit 21 with a time constant τ, and
Changes the attenuation rate in relation to the output of the integrator 22. The IF signal generated in the mixer 19 is transmitted to the IF
After passing through the narrow-band filter 26, it is attenuated by the IF attenuator 27, amplified by the IF amplifier 28, and sent to the next demodulator 33. The IF stage AGC detection circuit 29 detects the output level of the IF stage amplifier 28 and outputs a control signal to the IF stage attenuator 27 for maintaining the output level at a predetermined level. The integrator 30 integrates the output of the IF stage AGC detection circuit 29 with a time constant τ, and
27 changes the attenuation rate in relation to the output of the integrator 30. The demodulator 33 demodulates the input signal from the IF stage amplifier 28 and outputs it to the demodulated signal output terminal 34. The microcomputer 35 is a demodulator 33
, The time width Ts of a continuous sequence of nulls as a synchronization signal of a transmission frame is detected from the demodulated signal of
Are sent to the integrators 22 and 30 so that the time constant τ at is slightly longer than the time width Ts.

The operation of the AGC in the DAB car radio 10 will be described. Digital radio broadcasting including the service selected by the user has various transmission modes,
The time width Ts of the synchronization signal in the transmission frame differs depending on each transmission mode. The microcomputer 35 calculates the time width T of the synchronization signal in the transmission frame from the demodulated signal of the demodulator 33.
s is detected, and a control signal based on the detected
Send to 2,30. Thereby, the integrators 22 and 30 are connected to the RF stage A.
Integrating the attenuation rate control signals from the GC detection circuit 21 and the IF stage AGC detection circuit 29 with a time constant τ longer than the time width Ts;
The RF stage attenuator 18 and the IF stage attenuator 27 receive the integrated output of the integrators 22 and 30 as a control signal for the attenuation rate. Accordingly, during the reception period of the synchronization signal, the attenuation rates of the RF stage attenuator 18 and the IF stage attenuator 27 are suppressed from changing, that is, almost unchanged, despite the decrease in the output levels of the RF stage attenuator 18 and the IF stage attenuator 27. And the synchronization signal can be detected from the demodulated signal of the demodulator 33 without any trouble. On the other hand, the electric field strength of the received radio wave due to fading changes over a time sufficiently longer than the time width Ts of the synchronization signal.
Is sufficient to change the attenuation rate of the RF stage attenuator 18 and the IF stage attenuator 27.
The stage attenuator 18 and the IF stage attenuator 27 are integrators.
The attenuation rate is clearly changed by the outputs from 22 and 30, and the input level of the demodulator 33 becomes substantially a predetermined value. As a result, good A for the data portion following the synchronization signal in the transmission frame
GC can be performed.

In FIG. 1, the microcomputer 35 includes an integrator 2
The same control signal is sent to the integrators 22 and 30 so that the time constants τ of the integrators 22 and 30 are controlled to be the same. Can be made slightly different.

FIG. 2 is a block diagram of a main part of another car radio 40 for DAB. The DAB car radio 40 is, in order from the signal flow, an RF stage 41 as a front end and an IF stage.
Stage 42 and a demodulation stage including demodulator 76 are provided. RF stage
In 41, the antenna 45 receives the radio waves of all digital radio broadcasts where the current location of the DAB car radio 40 is the service area, and the RF signals of all these digital radio broadcasts are transmitted to the first broadband filter for the RF stage. After passing through 46, it is amplified in a variable gain RF stage amplifier 47, further passed through an RF stage second broadband filter 48, and then attenuated in an RF stage attenuator 49. PL
L52 sends a control signal to the first local oscillator 51 so that the first local oscillator 51 oscillates at an oscillation frequency related to the RF signal of the ensemble including the service selected by the user.
The first mixer 50 generates a first-stage IF signal by multiplying the input signal from the RF-stage attenuator 49 and the input signal from the first local oscillator 51. The RF stage AGC detection circuit 53 detects the output level of the first mixer 50 and outputs a control signal to the RF stage attenuator 49 for maintaining the output level at a predetermined level. The integrator 54 integrates the output of the RF stage AGC detection circuit 53 with a time constant τ, and the variable gain type RF stage amplifier 47 and RF stage attenuator 49 change the amplification factor and the attenuation factor in relation to the output of the integrator 22. Let it. No. 1 mixer
The first-stage IF signal generated at 50 passes through the IF-stage first narrow-band filter 59 at the IF stage 42,
After being attenuated in the F-stage first attenuator 60, it is further amplified in the IF-stage first amplifier 61 and sent to the second mixer 66. The IF stage first AGC detection circuit 62
It detects the output level of the stage first amplifier 61 and outputs a control signal to the IF stage first attenuator 60 for maintaining it at a predetermined level. The integrator 63 integrates the output of the IF stage first AGC detection circuit 62 with a time constant τ, and the IF stage first attenuator 60 changes the attenuation rate in relation to the output of the integrator 63. The second local oscillator 67 generates a signal of a fixed frequency. Generate. The second-stage IF signal passes through the second-stage IF narrow-band filter 68, is attenuated by the second-stage IF attenuator 69, and then amplified by the second-stage IF amplifier 70. The IF stage AGC detection circuit 71 is an IF stage second amplifier.
It detects the output level of 70 and outputs a control signal to the IF stage second attenuator 69 for maintaining it at a predetermined level. The integrator 72 integrates the output of the IF stage AGC detection circuit 71 with a time constant τ, and the IF stage second attenuator 69
The attenuation rate is changed in relation to the output of Demodulator 76 provides I
The input signal is demodulated from the F-stage second amplifier 70 and output to the demodulated signal output terminal 77. The microcomputer 78 detects the time width Ts of a continuous sequence of nulls as a synchronization signal of the transmission frame from the demodulated signal of the demodulator 76, and controls the time constant τ of the integrators 54, 63, and 72.

The operation of the AGC in the DAB car radio 40 will be described. Digital radio broadcasting including the service selected by the user has various transmission modes,
The time width Ts of the synchronization signal in the transmission frame differs for each transmission mode. The microcomputer 78 detects a time width Ts of a null string as a synchronization signal of each transmission frame in the demodulated signal from the demodulated signal from the demodulator 76, and
The control signal is sent to the integrators 54, 63, 72 so that the time constant τ in 63, 72 becomes a value slightly longer than the time width Ts.
Therefore, in the reception period of the synchronizing signal, the variable gain type RF stage amplifier 47, the RF stage attenuator 49, and the IF stage first attenuator despite the decrease in the input level of the demodulator 76.
Changes in the gains of the 60 and IF stage second attenuators 69 are suppressed, and the trouble-free detection of the synchronization signal from the demodulated signal of the demodulator 76 is guaranteed. On the other hand, the change in the electric field strength of the received radio wave due to fading or the like is sufficiently longer than the time width Ts of the synchronization signal.
Changes in the control signals of the AGC detection circuit 62 and the IF stage AGC detection circuit 71 depend on the variable gain type RF stage amplifier 47 and RF stage attenuator despite the integration in the integrators 54, 63 and 72.
49, the IF stage first attenuator 60 and the IF stage second attenuator 69 are sufficiently affected.
Broadband filter 48, RF stage attenuator 49, IF stage first
The attenuator 60 and the IF-stage second attenuator 69 can greatly change the amplification factor or the attenuation factor, and can perform good AGC on the data portion following the synchronization signal in the transmission frame.

In FIG. 2, the microcomputer 78 includes an integrator 5
The same control signal is sent to 4, 63, 72 and the integrators 54, 63, 7
Although the two time constants τ are controlled to be the same, a control signal may be sent through separate output lines to make the time constants τ of the integrators 54, 63, and 72 different from each other.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a DAB car radio.

FIG. 2 is a block diagram of a main part of another DAB car radio.

[Explanation of symbols]

Reference Signs List 10 Car radio for DAB (digital broadcasting receiver) 18 RF stage attenuator (gain control unit) 21 RF stage AGC detection circuit (AGC signal generation unit) 22 integrator 27 IF stage attenuator (gain control unit) 29 IF stage AGC detection circuit (AGC signal generator) 30 integrator 33 demodulator 40 DAB car radio (digital broadcast receiver) 41 RF stage 42 IF stage 47 Variable gain RF stage amplifier (gain control unit) 49 RF stage attenuator (gain control unit) 53 RF stage AGC detection circuit (AGC signal generation unit) 54 Integrator 60 IF stage first attenuator (gain control unit) 62 IF stage first AGC detection circuit (AGC signal generation unit) 63 Integrator 69 IF stage second attenuator (gain) Control section) 71 IF stage AGC detection circuit (AGC signal generation section) 72 integrator 76 demodulator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04B 1/16 H03G 3/20 H04H 1/00 H04J 11/00 H04L 27/00

Claims (4)

(57) [Claims] 1. A transmission frame having a synchronization signal consisting of a continuous sequence of a plurality of nulls at a head thereof, receiving a digital broadcast signal transmitted in units of the transmission frame, and selecting a digital broadcast signal from the selected digital broadcast signal. Demodulator (33,
AGC is performed so that the input level to the signal 76) becomes substantially a predetermined level irrespective of the electric field strength of the digital broadcast signal, and a plurality of transmissions in which the time width Ts of the synchronization signal differs depending on the transmission mode. A digital broadcast receiver (10, 40) adapted to receive a digital broadcast signal in a mode, detecting means for detecting a time width Ts of a synchronous signal of the selected digital broadcast signal , and receiving the synchronous signal. Control that controls the AGC response time according to the detection time width Ts so as to be longer than the detection time width Ts, while keeping the response time of the AGC as short as possible irrespective of the period.
Digital broadcasting receiver, characterized in that it comprises means. 2. The control of a response time of the AGC is performed in an RF stage.
2. The digital broadcast receiver according to claim 1, wherein the digital broadcast is performed in both (11, 41) and the IF stage (12, 42). 3. The method of controlling a response time of the AGC, comprising:
The signal generator (21, 29, 53, 62, 71) and the gain controller (18, 27, 47, 4)
9. The method according to claim 1, wherein the control is performed by controlling a time constant τ of an integrator (22, 30, 54, 63, 72) interposed between the first and second integrators (9, 60, 69). A digital broadcast receiver as described. 4. The digital signal according to claim 1, wherein the detection of the time width Ts of the synchronizing signal of the selected digital broadcast signal is detected from the output of the demodulator (33, 76). Broadcast receiver.