JP2002300053A - Broadcast receiver and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a car radio receiver 10 for DAB(digital audio broadcasting) that can suppress a noise output from a loudspeaker caused by an increased level of an RF signal outputted from a tracking filter 1 for processing a band III for an L band selection period. SOLUTION: Before switching an input of a band selection switch 20 from the band III to the L band, a control voltage at which the pass band of the tracking filter 18 includes no DAB reception signal of the band III is searched and the searched control voltage is determined for the control voltage of the tracking filter 18. The control voltage of the tracking filter 18 is maintained for the searched control voltage for the L band selection period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to, for example, DAB (D
digital Audio Broadcastin
The present invention relates to a broadcast receiver such as a car radio for g) and a control method thereof, and more particularly, to a broadcast receiver which switches a plurality of bands to be able to receive a broadcast of each band and a control method thereof.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a main part of a conventional DAB car radio 70. The same parts as those of the DAB car radio 10 according to the embodiment of the present invention, which will be described later, are designated by the same reference numerals, and description thereof will be omitted. Only the main points will be described.
DAB radio broadcasts include VHF band III and L band around 1.4 GHz.
The car radio 70 can receive radio broadcasts of both bands. The band filter 13 for the band III and the band filter 14 for the L band correspond to the band III and the L band, respectively, and are composed of a low-pass filter and a high-pass filter, respectively. In the DAB car radio 70, the band selection switch 20 selects the amplifier 19 side and the down converter 21 side, respectively, and selects the selected side according to whether the currently selected radio broadcast belongs to the band III or the L band. The detection device 29 is connected.

In a DAB car radio 70, a user
During the period when the L-band DAB is selected, the control voltage that determines the center frequency of the tracking filter 18 is not managed, and is not controlled before the switching, that is, before the switching.
When the DAB of III is selected, the DAB is left at the control voltage corresponding to the DAB, or is set to the ground voltage or the power supply voltage.

[0004]

In the conventional DAB car radio 70, for example, the area in which the car is running while listening to the L-band DAB is close to the band III DAB station, and If the frequency of the signal received from the DAB station happens to be equal to or close to the center frequency corresponding to the control voltage of the tracking filter 18, when the level of the signal received from the DAB station increases, the band selection switch 20 Despite the selection of the side, the effect of the increased output of the tracking filter 18 appears on the output side of the band selection switch 20 and is added as a disturbing signal to the reception signal of the DAB station of the selected L band. Sometimes. If the added value exceeds the threshold value, noise is output from the speaker.

An object of the present invention is to provide a broadcast receiver and a control method therefor which prevent a broadcast belonging to a band not selected by the band selecting means from being output as noise due to the presence of a tracking filter. That is.

[0006]

A broadcast receiver according to a first aspect of the present invention is provided with a first band filter for passing an RF signal having a frequency included in a first band, and an output side of the first band filter. Selects a tracking filter whose pass band is changed according to the control voltage, a filter for another band that passes an RF signal included in another band different in frequency from the first band, and a tracking filter side or another band filter side And a band selecting means for outputting the result to the detection stage. Then, the broadcast receiver performs a period during which the band selecting means selects the other band filter side (hereinafter, referred to as a band).
This period is called “other band selection period”. ) Has tracking filter control means for controlling the control voltage of the tracking filter so that the level of the output RF signal of the tracking filter becomes equal to or lower than a predetermined value.

[0007] The broadcast receiver is not limited to a radio broadcast receiver, but may be a television broadcast receiver. The broadcast receiver particularly includes a vehicle-mounted broadcast receiver and a DAB radio broadcast receiver. The number of bands that can be switched by the band selection means is not limited to two, and may be three or more. It is essential that a tracking filter is interposed between the first band filter and the band selecting means, but if a tracking filter is interposed between the other band filter and the band selecting means, , Even if not intervening. The first band filter and the other band filter are a high-pass filter, a low-pass filter,
And a bandpass filter or the like that meets the conditions is selected. If the broadcast receiver is a DAB radio broadcast receiver, for example, the first band is band III,
The other band is the L band.

When selecting a broadcast belonging to the first band, the control voltage for the other band selection period is controlled so that the received signal frequency of the broadcast falls within the pass band of the tracking filter. The control voltage for the other band selection period in the other band selection period may be set in advance by the user, or the broadcast receiver may search for an appropriate control voltage when switching from the first band to another band. It is good.

As a cause of noise output from the output means of the broadcast receiver such as a speaker due to the presence of the tracking filter during the other band selection period, that is, the period when the broadcast receiver outputs the broadcast belonging to the other band. Is
The center frequency of the tracking filter that determines the pass band of the tracking filter matches the frequency of the broadcast reception signal belonging to the first band, and the reception signal of the frequency temporarily increases, and the RF output from the tracking filter is output. The level of the signal may rise and appear at the output of the band selection means. On the other hand, in this broadcast receiver, the control voltage of the tracking filter during the other band selection period is a control voltage at which the output RF signal of the tracking filter becomes equal to or lower than a predetermined level. Even if the level of the received signal increases during the other band selection period, the received signal is outside the pass band of the tracking filter and is not transmitted to the output side of the tracking filter. As a result, it is possible to prevent the noise in the output of the broadcast receiver from increasing due to the level of the received signal of the broadcast belonging to the first band increasing during the other band selection period.

According to the broadcast receiver of the second invention, in the broadcast receiver of the first invention, the control voltage of the tracking filter is fixed during the other band selection period.

[0011] The fixed value of the control voltage of the tracking filter during the other band selection period is, for example, such that the frequency of the broadcast belonging to the first band does not exist in the pass band of the tracking filter corresponding to the fixed value. Value. During the other band selection period, the control voltage of the tracking filter at which the level of the output RF signal of the tracking filter becomes equal to or less than the predetermined value is periodically or appropriately searched, and the control voltage of the tracking filter is changed to the searched control voltage. However, by setting the control voltage of the tracking filter to a fixed value, the control of the control voltage of the tracking filter is simplified while the output of predetermined noise is suppressed.

According to the broadcast receiver of the third invention, in the broadcast receiver of the first or second invention, the tracking is performed before the band selecting means switches the selection from the tracking filter side to the other band filter side. The filter control means searches for the control voltage for the other band selection period, and switches the control voltage of the tracking filter to the searched control voltage for the other band selection period.

Before switching to the other band selection period, the tracking filter control means searches for the control voltage for the other band selection period for each switching. Therefore, when the broadcast receiver is, for example, a car radio, the control voltage can be set in the tracking filter to an appropriate control voltage for the other band selection period regardless of the driving region of the vehicle.

According to the broadcast receiver of the fourth invention, in the broadcast receiver of the third invention, the tracking filter control means changes the control voltage of the tracking filter in the increasing direction or the decreasing direction while changing the control voltage of the detection stage. The gain of the automatic gain control unit is detected, and the control voltage of the tracking filter when the gain becomes maximum is set to the control voltage for the other band selection period.

As another method of searching for the control voltage for the other band selection period, while scanning the pass band in the increasing or decreasing direction, an S meter or RSSI (Recei) of the detection stage is used.
veSignal Strength Indicat
There is also a method of searching for a pass band in which the electric field strength detected by ion) or the like becomes equal to or less than a reference value, and setting the searched pass band to a control voltage for another band selection period.

A broadcast receiver to which the control method of the fifth invention is applied is provided on a first band filter for passing an RF signal having a frequency included in the first band, and on an output side of the first band filter. Selects a tracking filter whose pass band is changed according to the control voltage, a filter for another band that passes an RF signal included in another band different in frequency from the first band, and a tracking filter side or another band filter side And a band selecting means for outputting the result to the detection stage. In the control method, the level of the output RF signal of the tracking filter is a predetermined value during a period in which the band selecting means selects the other band filter side (hereinafter, this period is referred to as “other band selection period”). The control voltage of the tracking filter is controlled as follows.

According to the control method of the broadcast receiver of the sixth invention, in the control method of the broadcast receiver of the fifth invention, the control voltage of the tracking filter is fixed during the other band selection period.

According to the control method of the broadcast receiver of the seventh invention, in the control method of the broadcast receiver of the fifth or sixth invention, the band selecting means selects from the tracking filter side to the other band filter side. Prior to the switching, the control voltage for the other band selection period is searched for, and the control voltage of the tracking filter is switched to the control voltage for the other band selection period searched.

According to the control method of the broadcast receiver of the eighth invention, in the control method of the broadcast receiver of the seventh invention, the control voltage of the tracking filter is changed while increasing or decreasing the control voltage of the tracking filter. The gain of the automatic gain control unit is detected, and the control voltage of the tracking filter when the gain becomes maximum is set to the control voltage for the other band selection period.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. Figure 1 shows a car radio 1 for DAB
0 is a main part block diagram of FIG. Band filter device 11
Is an antenna 1 for receiving DAB radio waves from a DAB broadcasting station.
2, and a band filter 13 for band III and a band filter 14 for L band, which respectively pass band III and L band reception signals. Band II
I belongs to the VHF band, and the L band is around 1.4 GHz. The tracking filter 18 has a center frequency determined in relation to the control voltage, and has a pass band as a predetermined range with respect to the center frequency. Of the RF signals output from the band filter 13 for band III, only the RF signals included in the pass band of the tracking filter 18 pass through the tracking filter 18. The amplifier 19 amplifies the RF signal from the tracking filter 18 and outputs it to the band selection switch 20. Down converter 21
Is an amplifier 22 for amplifying the RF signal from the L-band band filter 14, and an output of the amplifier 22 and an oscillator 24.
And a mixer 23 that mixes the signal with the signal from the band II and outputs the L-band RF signal to the band II.
Decrease the frequency to a frequency within the band of I. The band selection switch 20 includes an amplifier 19 and a down converter 21.
And an output terminal connected to one of the input terminals. Like the tracking filter 18, the tracking filter 28 limits the pass band of the RF signal that is allowed to pass. The band III DAB RF signal passes through the two tracking filters 18 and 28 to form a detector 29.
, The frequency band of the RF signal arriving at is further narrowed.

In the example shown in FIG. 1, the band filter 13 for band III is composed of a low-pass filter, the band filter 14 for L band is composed of a high-pass filter, and the tracking filters 18 and 28 are composed of band-pass filters. .

The detection device 29 has a mixer 30 and an automatic gain control unit 31. The mixer 30 receives the RF signal from the tracking filter 28 and a VCO (Voltage Con- trol).
An oscillation signal of a controlled oscillator (voltage controlled oscillator) 36 is mixed to generate an IF (intermediate frequency) signal of a predetermined frequency. The automatic gain control unit 31 controls the gain of an IF signal amplifier (not shown) so as to generate an IF signal of a predetermined level at a stage subsequent to the mixer 30. PLL (Phase Locked Loop)
The circuit 35 controls the VCO so that the VCO 36 outputs an oscillation signal of the frequency designated by the microprocessor 34.
Control the control voltage to 36. Microprocessor 34
Sends frequency information to the PLL circuit 35 so that the RF signal related to the radio broadcast specified by the user is converted into an IF signal in the detection device 29. The PLL circuit 35 has a VC
A voltage for controlling the oscillation frequency of O36 is output to VCO 36. In this way, the RF signal of the radio broadcast selected by the user is converted into an IF signal in the detector 29. The microprocessor 34 transmits information on the control voltage of the automatic gain control unit 31 to an ADC (Analog Digital).
Converter: analog-digital converter) 3
7 is input. The interface unit 39 outputs a digital signal input unit 40 to which an instruction signal from the microprocessor 34 is input, and an analog control voltage corresponding to the center frequency thereof to the tracking filters 18 and 28.
AC (Digital Analog Convert)
er: digital-analog converters) 41, 42, output ports 43, 44 for outputting control signals to a band III power supply 49 and an L-band power supply 50. band
The III power supply 49 and the L-band power supply 50 turn on and off the power supply to the amplifiers 19 and 22 based on the input signal from the interface unit 39.

While the user is selecting a band III DAB, the band selection switch 20 selects the amplifier 19 side. The center frequency of the tracking filter 18 is controlled via a control voltage to the tracking filter 18 so that the frequency of the corresponding broadcast signal is included in the pass band of the tracking filter 18. On the other hand,
While the user is selecting the L-band DAB, the band selection switch 20 selects the down converter 21 side. Thus, the RF signal corresponding to the DAB selected by the user is sent to the detection device 29 via the band selection switch 20 and the tracking filter 28. The RF signal input from the tracking filter 28 to the detector 29 is mixed in the mixer 30 with the oscillation signal from the VCO 36 and converted into a predetermined IF signal.

FIG. 2 is a flowchart of a program relating to the control voltage processing of the tracking filter 18 which is executed when switching the channel selection from the band III DAB to the L band DAB in the DAB car radio 10. Note that the control voltage to the tracking filter 18 changes the center frequency of the tracking filter 18, and
The pass band of the tracking filter 18 has a range of ± a predetermined amount around the center frequency of the tracking filter 18. In control voltage S60, band II before switching
The DAB of I is being received. In S61, the AGC (Auto Gain Controller) in the automatic gain control unit 31 is performed.
ol) Detect voltage. In S62, it is determined whether or not the AGC voltage detected in S61 is equal to or greater than the maximum value. If the determination is Yes, the process proceeds to S64, and if No, the process proceeds to S63. When the control voltage is set so that the pass band of the tracking filter 18 includes the reception frequency of any DAB of band III, the detection device 2
9 is supplied with an RF signal of a sufficiently high level from the tracking filter 28, the AGC voltage does not reach the maximum value, and the determination in S62 is No. On the contrary,
When the control voltage of the passing signal in the tracking filter 18 does not include the reception frequency of any DAB belonging to band III, the AGC voltage has the maximum value, and the determination in S62 is Yes. In S63, the center frequency X of the tracking filter 18 is increased by a predetermined amount ΔX, and in S6
Return to 1. When the scanning direction of the center frequency of the tracking filter 18 is not the increasing direction but the decreasing direction, the processing in S63 is not an increase of ΔX but a decrease. In this way, S61 to S63 are repeated until the AGC voltage becomes equal to or higher than the predetermined value, that is, until the pass band of the tracking filter 18 does not include the reception frequency of any DAB belonging to the band III. The center frequency is scanned. Then, when the AGC voltage exceeds a predetermined value, that is, when the center frequency of the tracking filter 18 reaches so that the pass band of the tracking filter 18 does not include the reception frequency of any DAB belonging to the band III, S64
Proceed to. In S64, the center frequency of the tracking filter 18 is fixed to the value X at the time of exiting from the loop of S61 to S63, and the input side of the band selection switch 20 is switched from the amplifier 19 to the down converter 21 side. Thus, in the L band selection period, the interface unit 39
The control voltage to the tracking filter 18 is controlled such that the pass band of the tracking filter 18 related to the center frequency of the tracking filter 18 does not include the reception signal of any DAB of the band III. Even if the automobile equipped with the DAB car radio 10 runs near the radio broadcasting station of the band III DAB during the L band selection period, tracking occurs even if the electric field strength of the received signal of the DAB of band III accidentally increases. Filter 18
The level of the RF signal output from is maintained at or below a predetermined value, and noise generation from the speaker due to the large output level of the tracking filter 18 during the L band selection period is prevented.

FIG. 3 is a block diagram of a main part when searching for the center frequency of the tracking filter 18 during the L band selection period instead of the AGC voltage of the detector 29. The detector 29 is an RSSI (Receive Signal S).
strength indication) or an S-meter 69, and the RSSI or S-meter 69 receives the R signal input from the tracking filter 28.
The RSSI or electric field strength of the corresponding DAB reception signal is detected from the F signal. (A) The above-mentioned AGC voltage becomes small when the pass signal of the tracking filter 18 contains the received signal of the band III DAB,
(B) The RSSI and the electric field strength become large when the pass band of the tracking filter 18 contains the reception signal of the band III DAB, that is, the magnitude relation of the detection voltage between (a) and (b). Is reversed, the output of the RSSI or S meter 69 is input to the ADC 37 of the microprocessor 34 via the inverter 70. Thus, A
Searching for the control voltage of the tracking filter 18 that can sufficiently suppress the output level of the tracking filter 18 during the L band selection period by using the RSSI or the RSSI or the electric field strength detected by the S meter 69 instead of the GC voltage. Can be.

FIG. 4 is an additional circuit diagram when the detected value of the AGC voltage of the automatic gain controller 31 is input to the analog input port 75 of the microprocessor 34. A reference voltage intermediate between the power supply voltage Vcc and the ground voltage is applied to the inverting input terminal of the comparator 73 via voltage dividing resistors 76 and 77.
The AGC voltage from the automatic gain controller 31 is input to the non-inverting input terminal of the comparator 73. The reference voltage is set to a value slightly lower than the maximum value of the AGC voltage. Thus, the output of the comparator 73 is at a low level when the AGC voltage is lower than the reference voltage, and at a high level when the AGC voltage reaches near the maximum value. The microprocessor 34 outputs the output of the comparator 73 to the analog input port 75.
And determines whether or not the pass band of the tracking filter 18 includes the frequency of the DAB reception signal of band III based on this input.

[Brief description of the drawings]

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

FIG. 2 DA of band III in DAB car radio
It is a flowchart of the program which concerns on the control voltage process of a tracking filter performed when switching channel selection from B to L-band DAB.

FIG. 3 is a block diagram of a main part when searching for a center frequency of a tracking filter during an L band selection period instead of the AGC voltage of the detector.

FIG. 4 is an additional circuit diagram when the detected value of the AGC voltage of the automatic gain control unit is input to an analog input port of a microprocessor.

FIG. 5 is a block diagram of a main part of a conventional DAB car radio.

[Explanation of symbols]

Reference Signs List 10 Car radio for DAB (broadcast receiver) 13 Band filter for band III (first band filter) 14 Band filter for L band (filter for other bands) 18 Tracking filter 20 Band selection switch (band selection means) 39 Interface (Tracking filter control means)

Claims (8)

[Claims] A first band filter that passes an RF signal having a frequency included in a first band; a tracking filter that is provided on an output side of the first band filter and that changes a pass band according to a control voltage. R included in another band different in frequency from the first band
In a broadcast receiver, comprising: a filter for another band that allows an F signal to pass therethrough; and a band selection unit that selects a tracking filter or a filter for another band and outputs the selected band to a detection stage. The control voltage of the tracking filter is controlled such that the level of the output RF signal of the tracking filter becomes equal to or less than a predetermined value during a period when the filter for the side is selected (hereinafter, this period is referred to as “other band selection period”). And a tracking filter control means. 2. The broadcast receiver according to claim 1, wherein the control voltage of the tracking filter is fixed during another band selection period. 3. The tracking filter control means searches for the control voltage for the other band selection period before the band selection means switches the selection from the tracking filter side to the other band filter side. 3. The broadcast receiver according to claim 1, wherein the control voltage of the tracking filter is switched to the searched control voltage for another band selection period. 4. The tracking filter control means,
While changing the control voltage of the tracking filter in the increasing direction or the decreasing direction, the gain of the automatic gain control unit of the detection stage is detected, and the control voltage of the tracking filter when the gain reaches the maximum is selected for another band. The broadcast receiver according to claim 3, wherein the broadcast control voltage is set to a period control voltage. 5. A first band filter for passing an RF signal having a frequency included in a first band, a tracking filter provided on an output side of the first band filter and changing a pass band according to a control voltage. R included in another band different in frequency from the first band
A method for controlling a broadcast receiver, comprising: a filter for another band that allows an F signal to pass therethrough; and a band selector for selecting a tracking filter or a filter for another band and outputting the selected signal to a detection stage. During the period in which the filter for the other band is selected (hereinafter, this period is referred to as “other band selection period”), the control of the tracking filter is performed so that the level of the output RF signal of the tracking filter becomes equal to or less than a predetermined value. A method for controlling a broadcast receiver, comprising controlling a voltage. 6. The method according to claim 5, wherein the control voltage of the tracking filter is fixed during the other band selection period. 7. Prior to the band selecting means switching the selection from the tracking filter side to the other band filter side, the control voltage for the other band selection period is searched for, and the control voltage of the tracking filter is changed to 7. The control method for a broadcast receiver according to claim 5, wherein the control voltage is switched to the searched control voltage for another band selection period. 8. The gain of an automatic gain control section of the detection stage is detected while changing the control voltage of the tracking filter in an increasing direction or a decreasing direction, and the tracking filter is controlled when the gain becomes maximum. The method according to claim 7, wherein the voltage is set to a control voltage for another band selection period.