JP2008005139A - Terrestrial wave digital tuner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a terrestrial digital tuner capable of acquiring an accurate input level of a desired wave, when an antenna is installed or field intensity is measured during maintenance. <P>SOLUTION: When a contact of SW 33 is pushed down towards a terminal (b), only disturbance wave is attenuated and removed by a SAW filter 15 if both of a desired wave and a disturbance wave exist. Accordingly, an AGC detecting circuit 24 of RF-AGC outputs an AGC control signal according to a received power of a desired wave only. As mentioned above, an AGC gain value of RF-AGC, an AGC gain value of IF-AGC, and a tuner output, i.e. an IF output 21 are measured in a status that AGC is performed. Then, an accurate received power of the desired wave can be computed according to these measured values. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a terrestrial digital tuner having an AGC circuit that accurately measures the electric field strength of a desired wave signal.

  2. Description of the Related Art Conventionally, in a terrestrial digital tuner built-in device such as a television, the signal level input to an OFDM (Orthogonal Frequency Division Multiplexing) demodulating IC is constant even if the magnitude (electric field strength) of the signal input to the tuner changes. AGC (Auto Gain Control) is applied so as to become.

  Here, the configuration and operation of the AGC will be schematically described with reference to FIGS. 2 and 3 showing the configuration of a conventional terrestrial digital tuner.

  FIG. 2 is a block diagram illustrating a configuration example of a conventional terrestrial tuner, and FIG. 3 is a diagram illustrating an AGC characteristic indicating a relationship between an AGC gain and an input signal level.

  The broadcast wave RF signal input from the RF input terminal 1 is input to the RF amplifier 4 after the unnecessary signal in the low frequency band is removed by the HPF 3, and the output is input to the RF distributor 5.

  The RF amplifier 4 compensates for gain loss in the HPF 3 and the RF distributor 5, and the RF distributor 5 distributes and outputs one input signal in two. Of the two output signals, a is connected to an internal circuit of the tuner (band switching circuit 6 and later), and b is connected to the RF distribution output terminal 2. The RF signal output from the RF distribution output terminal 2 is input to the second tuner.

  Next, the circuits 7, 8 and 9 are high frequency amplifier circuits in respective bands (UHF, VHF-high, VHF-low), and the signal a output from the RF distributor 5 is a band selected by the band switching circuit 6. Connected to. The band switching circuit 6 is controlled by the PLL-IC 20 to select which band.

  Here, when c is selected, the RF signal a is output only to the UHF band 7 and is not output to the VHF-high band 8 and the VHF-low band 9. The BPF 10 is an input tuning band-pass filter that passes only the UHF band, and the amplifier 11 is a variable gain RF amplifier, and the gain is adjusted by the voltage applied to the RF-AGC terminal 22.

  When the signal level entering the RF input terminal 1 is high, the gain is reduced so as not to cause distortion in the subsequent circuit, and when the signal level is low, the gain is controlled so as not to deteriorate NF (noise figure). To do. A signal output from the amplifier 11 is connected to the BPF 12. The BPF 12 is a tracking filter whose pass band changes in synchronization with the oscillation frequency of a VCO (Voltage Controlled Oscillator) 19 so as to pass only a desired reception channel by an interstage band pass filter.

The VCO 19 is a voltage controlled oscillator controlled by a PLL (Phase Locked Loop) circuit 20 (whose oscillation frequency changes depending on a tuning voltage to be applied) and oscillates a local oscillation signal in the UHF band. The local oscillation signal and the RF signal output from the BPF 12 are frequency-converted to IF (intermediate frequency) by the mixer 13. Here, the local oscillation frequency (fvco), the RF frequency (frf), and the IF frequency (fif) are:
fvco-frf = fif
The fif always has a constant frequency.

  In the band switching circuit 6, the VHF-high band 8 or VHF-low band 9 high-frequency amplifier operates even when d or e is selected.

  The high-frequency amplifier circuits 7, 8 and 9 have different frequency bands to be processed, but the role of each circuit is the same as the UHF band 7. The IF signal output from the IF amplifier 14 is input to the BPF 15. The BPF 15 generally uses a SAW filter that can sharply drop out of band, and removes unnecessary out-of-band signals such as adjacent channels that cannot be removed by the BPF 12.

  The IF signal output from the BPF 15 is output to the IF output terminal 21 through the amplifier 16. The amplifier 16 is a variable gain IF amplifier, and the gain is adjusted by the voltage applied to the IF-AGC terminal 23. The IF signal output to the IF output terminal 21 is adjusted by the variable gain RF amplifier and the variable gain IF amplifier so that the RF signal input to the RF input terminal 1 is always at a constant level regardless of the level. To the demodulator circuit.

  Note that the block diagram shown in FIG. 2 is an example. When the RF distribution output is not required, the circuits 2 and 5 are unnecessary, and VHF-high and VHF-low are processed in one band without being divided. Various configurations are possible.

  Next, the AGC operation of the terrestrial digital tuner having the above configuration will be described with reference to FIG.

  First, in the state where the signal level on the left end side of the horizontal axis shown in FIG. 3 is extremely weak, RF-AGC (22) and IF-AGC are not applied and the maximum gain state is obtained, and the total gain of the entire circuit is maximized. Yes.

  When the input signal level gradually rises from the weak input state, IF-AGC starts to be applied first, and when it exceeds a certain level, RF-AGC is applied next. This point at a certain level is called TOP (Take Over Point) and is usually settable by the user who uses the tuner.

  Here, if the RF-AGC is applied too early (in a weak input state), the gain at the RF stage decreases, and the NF of the tuner main body deteriorates. On the other hand, if RF-AGC is applied too slowly (in a strong input state), distortion in the RF stage or the mixer tends to occur. Therefore, the balance between the two is important for setting the TOP.

  When the level of the input signal is further increased from the above state, the RF-AGC and IF-AGC are finally saturated and become the minimum gain, and the total gain becomes the minimum.

  Thus, within the range of the total gain line area shown in FIG. 3, the electric field of the input signal to the tuner from the RF-AGC gain value, IF-AGC gain value, and the output level set to a predetermined value is set. You can know the strength.

  Patent Document 1 also has a plurality of variable gain amplifiers, and supplies the AGC control voltage of a detector that generates an AGC control signal from the output of each amplifier to each amplifier, and adds the outputs of each amplifier. A technique for calculating the electric field strength from the obtained overall gain and a predetermined signal level is disclosed.

  Next, an operation when an interference wave such as an analog signal having a level higher than that of the desired wave is input to a region adjacent to the desired wave will be described with reference to FIG.

  The diagrams from FIG. 4A to FIG. 4C show the AGC-controlled input levels of the respective units in a state where only the desired wave is received. Also, (d) to (f) are diagrams showing the AGC-controlled input levels of each part when there is an interference wave having a level larger than the desired wave adjacent to the desired wave signal.

  FIG. 4A shows the input level of the desired wave to the tuner. As shown in (b) and (c), since only the desired wave exists, AGC is applied according to the power of only the desired wave signal, so that the input levels of IF-AMP and OFDM-IC are the same level. Will be controlled.

  On the other hand, as shown in FIG. 4 (d), if there is an adjacent interference signal, the RF-AGC is applied to the desired signal + interference signal, so that the level is higher than the desired signal level shown in FIG. 4 (b). Is attenuated. Then, after the interference wave is removed by the SAW filter 15, as shown in (f), the level of the desired wave is controlled to a predetermined level (the level shown in (c)) by the IF-AGC, so that the OFDM-IC Entered.

As described above, the RF-AGC in the terrestrial digital tuner is provided with an AGC detection circuit at the mixer output stage (the front stage of the SAW filter) to improve resistance against interference caused by an analog signal adjacent to the desired wave. Thus, a feedback loop is configured to perform AGC control.
JP-A-1-318434

  However, in the conventional RF-AGC method, when an interference wave such as an adjacent analog signal larger than the desired wave is input, the RF-AGC is applied to the total power of the desired wave and the interference wave. Although it is effective in reducing the occurrence of distortion at the mixer stage, the desired wave is also attenuated. For example, when measuring the radio field intensity during antenna installation or maintenance, the exact radio field intensity of the desired wave is not known. There is a problem of disappearing.

  Accordingly, the present invention has been made in view of the above-described problems, and is a terrestrial digital tuner that acquires an accurate input level of a desired wave when measuring radio wave intensity at the time of antenna installation or maintenance. Is to provide.

  In order to solve the above problems, a terrestrial digital tuner according to the present invention has the following features.

  The terrestrial digital tuner according to the present invention is a terrestrial digital tuner including a multi-stage AGC control circuit including a bandpass filter for removing an interference wave existing in a frequency region adjacent to a desired wave and an AGC detection circuit. In addition, a switch is provided between the input and output of the band-pass filter, and the switch switches to the input signal of the band-pass filter when the digital tuner is performing a normal operation, including when an antenna is installed. When measuring the received input power of the desired wave, an operation of switching to the output signal of the bandpass filter is performed, the switched input signal or output signal is supplied to the AGC detection circuit, and the multistage AGC control is performed. From the total AGC gain obtained by adding the AGC gain of the circuit and the final output value of the terrestrial digital tuner Characterized in that to calculate the accurate received power value of the desired signal.

  In the terrestrial digital tuner according to the present invention, the switch is provided in an AGC control circuit in a first stage among the multi-stage AGC circuits.

  In the terrestrial digital tuner according to the present invention, the multi-stage AGC control circuit has two stages of an initial stage RF-AGC control circuit and an intermediate frequency stage IF-AGC control circuit.

  As described above, according to the terrestrial digital tuner according to the present invention, after removing the interference wave component in the first stage AGC control loop in the multi-stage AGC control loop, AGC control is performed using only the desired wave component, An excellent effect can be obtained in that the accurate received power of the desired wave can be calculated from the combined value of the respective AGC control gains.

  Hereinafter, an embodiment of a terrestrial digital tuner according to the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram of a terrestrial digital tuner according to the present invention.

  FIG. 1 is an example of an embodiment of the invention. In the figure, the same reference numerals as those in FIG. 2 denote the same components, and the basic configuration is the same as the conventional one shown in the figure.

  As shown in FIG. 1, since the basic configuration is the same as the conventional configuration, the description of each component] and the overall schematic operation description are omitted here.

  The difference from the prior art is that a switch (SW) 33 is newly provided.

  The following description will focus on the operation of SW33.

  The terminal a of the SW 33 is connected to the input of the SWA filter, that is, the output side of the IF amplifier 14, and the terminal b is connected to the output of the SAW filter, that is, the input side of the gain variable RF amplifier 16.

  The terminal c is connected to the input side of the AGC detection circuit. The SW 33 operates so that the contact point of the switch is switched to either the terminal a or the terminal b.

  At the time of normal operation, the contact of the SW 33 is tilted to the terminal a as in the conventional case, and the output signal of the IF amplifier is input to the AGC detection circuit.

  As described above, when both the desired wave and the jamming wave exist, the RF-AGC is controlled by the total power of the desired wave and the jamming wave.

  On the other hand, when the contact of SW33 is brought down to terminal b, when both the desired wave and the disturbing wave exist, only the disturbing wave is attenuated and removed by the SAW filter 15, so that AGC detection of the RF-AGC is performed. The circuit 24 outputs an AGC control signal corresponding to the received power of only the desired wave.

  As a result, AGC control can be performed in the state shown in FIG.

  Here, the interference wave component is removed by the SAW filter 15, but any other device type can be used as long as it is a steep band removal filter.

  As described above, the AGC gain value of the RF-AGC, the AGC gain value of the IF-AGC, and the tuner output, that is, the IF output 21, are measured in the state where the AGC control is performed as described above. From this, it is possible to calculate the accurate received power of the desired wave.

  Therefore, at the time of initial installation or maintenance when determining the direction of the antenna, the reception power of the desired wave can be obtained by tilting the contact of the SW 33 to the terminal b to form an RF-AGC control loop.

  As shown in FIG. 1, the SW 33 is controlled by receiving a control signal from the PLL circuit 20 that also controls the entire tuner body, for example.

  This control signal may be generated by a notification signal by the user at the time of initial installation or the like.

  As described above, in the first stage AGC control loop in the multi-stage AGC control loop, after the interference wave component is removed, AGC control is performed using only the desired wave component, and the desired wave is determined from the combined value of each AGC control gain. It is possible to accurately calculate the received power.

  It should be noted that the terrestrial digital tuner according to the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

1 is a block diagram of a terrestrial digital tuner according to the present invention. FIG. It is a block diagram which shows the structural example of the conventional terrestrial tuner. It is a figure which shows the AGC characteristic which shows the relationship of the AGC gain with respect to an input signal level. (A)-(c) is a figure which shows the input level by which AGC control of each part in the state which has received only the desired wave. Also, (d) to (f) are diagrams showing the AGC-controlled input levels of each part when there is an interference wave having a level larger than the desired wave adjacent to the desired wave signal.

Explanation of symbols

1 RF input terminal 2 RF distribution output terminal 3 HPF
4 RF amplifier 5 RF distributor 6 Band switching circuit 7 UHF band 8 VHF-high band 9 VHF-low band 10 BPF
11 Variable gain RF amplifier 12 BPF (tracking filter)
13 Mixer 14 IF amplifier 15 BPF (SAW filter)
16 Gain variable IF amplifier 17 VHF-low VCO
18 VHF-high VCO
19 UHF VCO
20 PLL circuit 21 IF output 22 RF-AGC
23 IF-AGC terminal 24 AGC detection circuit 25 RF-AGC monitor terminal 26 OFDM demodulation IC
27 AD converter 28 Dual AGC control circuit 29 OFDM demodulation / FEC circuit 30 AGC1 (RF-AGC) output terminal 31 AGC2 (IF-AGC) output terminal 32 TS output terminal 33 SW

Claims (3)

A terrestrial digital tuner comprising a multi-stage AGC control circuit including a band-pass filter for removing an interference wave existing in a frequency region adjacent to a desired wave, and an AGC detection circuit,
A switch is provided between the input and output of the bandpass filter,
The switch is switched to the input signal of the band-pass filter when the digital tuner is performing a normal operation, and when measuring the received input power of the desired wave including when an antenna is installed, An operation of switching to an output signal of a band pass filter is performed, and the switched input signal or output signal is supplied to the AGC detection circuit,
An accurate received power value of the desired wave is calculated from a total AGC gain obtained by adding AGC gains of the multi-stage AGC control circuit and a final output value of the terrestrial digital tuner. Wave digital tuner.   2. The terrestrial digital tuner according to claim 1, wherein the switch is provided in an AGC control circuit in a first stage among the multi-stage AGC circuits.   3. The terrestrial digital tuner according to claim 1, wherein the multi-stage AGC control circuit includes two stages of an initial stage RF-AGC control circuit and an intermediate frequency stage IF-AGC control circuit.

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