JP3668655B2 - AGC circuit - Google Patents

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JP3668655B2
JP3668655B2 JP31635699A JP31635699A JP3668655B2 JP 3668655 B2 JP3668655 B2 JP 3668655B2 JP 31635699 A JP31635699 A JP 31635699A JP 31635699 A JP31635699 A JP 31635699A JP 3668655 B2 JP3668655 B2 JP 3668655B2
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intermediate frequency
band
signal
pass filter
television signal
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JP2001136462A (en
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憲人 岡田
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Alps Alpine Co Ltd
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Alps Electric Co Ltd
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Description

【０００１】
【発明の属する技術分野】
本発明は、テレビジョン信号送信機等に使用されるＡＧＣ回路に関し、詳しくは、アナログテレビジョン信号またはデジタルテレビジョン信号を送信するＣＡＴＶシステム用のテレビジョン信号送信機に好適なＡＧＣ回路に関する。
【０００２】
【従来の技術】
図４は従来のＡＧＣ回路であり、テレビジョンの中間周波数帯の信号（中間周波信号という）が入力される信号レベル制御手段２１は可変減衰回路あるいは可変利得増幅回路等から構成され、その出力レベルはＡＧＣ電圧によって制御される。この中間周波信号としては、受信した他のテレビジョン信号の再送信のための中間周波信号が用いられたり、録画した自主制作番組のための中間周波信号が用いられたりするが、いずれにしても、音声中間周波信号の周波数（音声中間周波数という）よりも映像中間周波信号の周波数（映像中間周波数という）が高く、例えば、米国仕様では音声中間周波信号は４１．２５ＭＨｚ、映像中間周波信号は４５．７５ＭＨｚである。
【０００３】
そして、信号レベル制御手段２１から出力された中間周波信号は図示しない周波数変換回路によって所定のチャンネルのテレビジョン信号に周波数変換され、ＣＡＴＶシステム等の加入者に送信される。
【０００４】
一方、信号レベル制御手段２１から出力された中間周波信号は、映像中間周波信号を抽出するフィルタ手段２２にも入力される。フィルタ手段２２は、例えば、映像中間周波数に同調する単同調回路等のバンドパスフィルタや、音声中間周波数と映像中間周波数との間にカットオフ周波数を有するハイパスフィルタや、音声中間周波数を減衰するトラップ回路等のバンドエルミネートフィルタ（帯域消去フィルタ）等で構成される。
従って、フィルタ手段２２は音声中間周波信号を除去して映像中間周波信号のみを抽出する。
【０００５】
抽出された映像中間周波信号は中間周波増幅回路２３によって増幅された後、検波手段２４によって検波され、中間周波信号のレベルに比例する直流電圧（検波電圧）が得られる。検波手段２４は二個のダイオード２４ａ、２４ｂからなる周知のダイオード検波回路等で構成される。
【０００６】
検波電圧は直流増幅回路２５によって所定のレベルまで増幅され、その出力電圧はＡＧＣ電圧として信号レベル制御手段２１の制御端に入力される。
【０００７】
以上の構成において、検波電圧は入力された中間周波信号のレベルに比例して出力されるので、この電圧をＡＧＣ電圧として信号レベル制御手段２１に入力することで信号レベル制御手段２１から出力される中間周波信号のレベルはほぼ一定となるように制御される。
【０００８】
【発明が解決しようとする課題】
しかし、従来のＡＧＣ回路は、既存のアナログテレビジョン信号に対応するものであり、フィルタ手段によって音声中間周波数帯が減衰しているので、デジタルテレビジョン信号の送信時にこのまま使用すると、検波手段から出力される検波電圧が低下して正確なＡＧＣ動作が行われないという問題が発生する。
【０００９】
即ち、デジタルテレビジョン信号においては、アナログテレビジョン信号のように、映像信号および音声信号によってそれぞれ変調される特定の搬送波が存在せず、中間周波数帯の全域における極めて多数の周波数（数百乃至数千）成分が映像信号及び音声信号に基づくデジタル信号によってデジタル変調されている。そのため、音声中間周波数帯が減衰していると、その分だけ検波手段に入力されるデジタルテレビジョン信号の電力が低下し、その結果、検波電圧が低下する。
【００１０】
そこで、本発明のＡＧＣ回路は、アナログテレビジョン信号の送信時とデジタルテレビジョン信号の送信時とのいずれにおいても確実にＡＧＣがかかるようにすることを目的とする。
【００１１】
上記の課題を解決する手段として、本発明のＡＧＣ回路は、アナログテレビジョン信号又はデジタルテレビジョン信号に基づく中間周波数帯のテレビジョン信号が入力され、ＡＧＣ電圧によって前記中間周波数帯のテレビジョン信号のレベルを変えて出力する信号レベル制御手段と、前記信号レベル制御手段から出力される前記中間周波数帯のテレビジョン信号を検波して直流電圧を出力すると共に前記直流電圧を前記ＡＧＣ電圧として前記信号レベル制御手段に入力する検波手段とを備え、前記信号レベル制御手段の出力端と前記検波手段の入力端との間には、受信チャンネルの前記中間周波数帯における音声中間周波数の信号の通過を阻止して映像中間周波数の信号を通過する第一の帯域通過手段と、少なくとも前記受信チャンネルの中間周波数帯における全ての信号を通過する第二の帯域通過手段とからなる帯域選択手段を設け、前記信号レベル制御手段に前記アナログテレビジョン信号に基づく中間周波数帯のテレビジョン信号が入力されたときには前記第一の帯域通過手段を介して前記中間周波数帯のテレビジョン信号を前記検波手段に入力し、前記デジタルテレビジョン信号に基づく中間周波数帯のテレビジョン信号が入力されたときには前記第二の帯域通過手段を介して前記中間周波数帯のテレビジョン信号を前記検波手段に入力した。
【００１２】
また、本発明のＡＧＣ回路は、前記第一の帯域通過手段を第一のバンドパスフィルタで構成し、前記信号レベル制御手段を前記検波手段に接続するバイパス線路で前記第二の帯域通過手段を構成した。
【００１３】
また、本発明のＡＧＣ回路は、前記第一の帯域通過手段を第一のバンドパスフィルタで構成し、前記中間周波数帯域を通過帯域とする第二のバンドパスフィルタで前記第二の帯域通過手段を構成した。
【００１４】
また、本発明のＡＧＣ回路は、前記帯域選択手段には前記中間周波数帯域のほぼ最高周波数をカットオフ周波数とするローパスフィルタと、前記音声中間周波数と前記映像中間周波数との間にカットオフ周波数を有する第一のハイパスフィルタと、前記中間周波数帯のほぼ最低周波数をカットオフ周波数とする第二のハイパスフィルタとを設け、前記信号レベル制御手段に前記アナログテレビジョン信号に基づく中間周波数帯の信号が入力されたときには前記ローパスフィルタと前記第一のハイパスフィルタとを直列に接続すると共に前記第一の帯域通過手段を構成し、前記デジタルテレビジョン信号の基づく中間周波数帯の信号が入力されたときには前記ローパスフィルタと前記第二のハイパスフィルタとを直列に接続すると共に前記第二の帯域通過手段を構成した。
【００１５】
【発明の実施の形態】
以下、本発明のＡＧＣ回路を図面に従って説明する。図１は本発明のＡＧＣ回路の第一の実施の形態を示す回路図であり、アナログテレビジョン信号又はデジタルテレビジョン信号に基づく中間周波数帯のテレビジョン信号（中間周波信号という）は信号レベル制御手段１に入力される。信号レベル制御手段１は可変減衰回路あるいは可変利得増幅回路等から構成され、その出力レベルはＡＧＣ電圧によって制御される。
【００１６】
ここで、中間周波信号としては、受信した他のシステムのテレビジョン信号に基づくものが用いられたり、録画した自主制作番組に基づくものが用いられたりするが、アナログテレビジョン信号の基づく場合は、音声中間周波信号の周波数（音声中間周波数という）よりも映像中間周波信号の周波数（映像中間周波数という）が高く、例えば、米国仕様では音声中間周波信号は４１．２５ＭＨｚ、映像中間周波信号は４５．７５ＭＨｚとなっている。
【００１７】
一方、デジタルテレビジョン信号に基づく中間周波信号である場合では、中間周波数帯の全域における極めて多数の周波数（数百乃至数千）成分が映像信号及び音声信号に基づくデジタル信号によってデジタル変調されているため、特定の映像搬送及び音声搬送波は存在しない。
【００１８】
そして、信号レベル制御手段１から出力された中間周波信号は図示しない周波数変換回路によって所定のチャンネルのテレビジョン信号に周波数変換され、ＣＡＴＶシステム等の加入者に送信される。
【００１９】
一方、信号レベル制御手段１から出力された中間周波信号は、帯域選択手段２に入力される。帯域選択手段２は、受信チャンネルにおける中間周波数帯における映像中間周波数を通過し、音声中間周波数を阻止する第一の帯域通過手段である第一のバンドパスフィルタ３と、少なくとも中間周波数帯の全体域を通過する第二の帯域通過手段であるバイパス線路４と切替手段５、６とを有し、切替手段５、６によって第一のバンドパスフィルタ３またはバイパス線路４のいずれかが選択される。
【００２０】
そして、中間周波信号は第一のバンドパスフィルタ３又はバイパス線路４のいずれかを介して中間周波増幅回路７に入力される。ここで増幅された中間周波信号は検波手段８によって検波されて直流電圧（検波電圧）を出力する。検波電圧は信号レベル制御手段１に入力される中間周波信号のレベルに比例する。検波手段８は二個の検波ダイオード８ａ、８ｂからなる周知のダイオード検波回路等で構成される。
【００２１】
検波電圧は直流増幅回路９によって所定のレベルまで増幅され、その出力電圧はＡＧＣ電圧として信号レベル制御手段１の制御端に入力される。この結果、信号レベル制御手段１から出力される中間周波信号のレベルはほぼ一定となるように制御される。
【００２２】
以上の構成において、帯域選択手段２においては、信号レベル制御手段１に入力される中間周波信号がアナログテレビジョン信号に基づくものであれば第一のバンドパスフィルタ３が選択される。すると、検波手段８からは映像中間周波信号のみによる検波電圧が得られる。この結果、信号レベル制御手段１は映像信号に基づいてＡＧＣ動作が行われる。
【００２３】
一方、信号レベル制御手段１に入力される中間周波信号がデジタルテレビジョン信号に基づくものであれば、バイパス線路４が選択される。この結果、中間周波数帯の全体域の信号が検波されるので、検波電圧の低下はない。そして、第二の帯域通過手段としてバイパス線路４を用いるので構成が簡単となる。
【００２４】
図２は本発明のＡＧＣ回路における第二の実施の形態を示し、図１に示すバイパス線路４の代わりに第二のバンドパスフィルタ１１を設けた構成となっている。第二のバンドパスフィルタ１１は中間周波数帯の全体域を通過帯域とするように構成されている。従って、信号レベル制御手段１に入力される中間周波信号がデジタルテレビジョン信号に基づくものであれば、第二のバンドパスフィルタ１１が選択されて中間周波数帯の全体域の信号が検波手段８に入力される。そして、第二の帯域通過手段として第二のバンドパスフィルタ１１を用いるので、中間周波数帯域外の信号による誤った検波電圧を検波することもない。
【００２５】
図３は本発明のＡＧＣ回路における第三の実施の形態を示し、帯域選択手段２はローパスフィルタ１２と第一のハイパスフィルタ１３と第二のハイパスフィルタ１４とを有している。そして、切替手段５、６によって第一のハイパスフィルタ１３又は第二のハイパスフィルタ１４が直列に接続されるようになっている。
【００２６】
ローパスフィルタ１２は中間周波数帯域のほぼ最高周波数にカットオフ周波数を有し、第一のハイパスフィルタ１３は中間周波数帯域における音声中間周波数と映像中間周波数との間にカットオフ周波数を有し、また、第二のハイパスフィルタ１４は、中間周波数地域のほぼ最低周波数にカットオフ周波数を有している。
【００２７】
そして、信号レベル制御手段にアナログテレビジョン信号に基づく中間周波数帯の信号が入力されたときには、第一のハイパスフィルタ１３を選択してローパスフィルタと第一のハイパスフィルタとを直列に接続すると共に第一の帯域通過手段を構成し、デジタルテレビジョン信号の基づく中間周波数帯の信号が入力されたときには第二のハイパスフィルタ１４を選択してローパスフィルタと第二のハイパスフィルタとを直列に接続すると共に第二の帯域通過手段を構成するようにしている。
【００２８】
この結果、信号レベル制御手段１に入力される中間周波信号がアナログテレビジョン信号に基づくものであれば、映像中間周波信号のみが検波手段８に入力される。
一方、信号レベル制御手段１に入力される中間周波信号がデジタルテレビジョン信号に基づくものであれば、中間周波数帯の全体域における信号が検波手段８に入力され、正確な検波電圧が得られる。
【００２９】
【発明の効果】
以上のように、本発明のＡＧＣ回路は、信号レベル制御手段の出力端と検波手段の入力端との間には、受信チャンネルの中間周波数帯における音声中間周波数の信号の通過を阻止して映像中間周波数の信号を通過する第一の帯域通過手段と、少なくとも前記受信チャンネルの中間周波数帯における全ての信号を通過する第二の帯域通過手段とからなる帯域選択手段を設け、前記信号レベル制御手段に前記アナログテレビジョン信号に基づく中間周波数帯のテレビジョン信号が入力されたときには前記第一の帯域通過手段を介して前記中間周波数帯のテレビジョン信号を前記検波手段に入力し、前記デジタルテレビジョン信号に基づく中間周波数帯のテレビジョン信号が入力されたときには前記第二の帯域通過手段を介して前記中間周波数帯のテレビジョン信号を前記検波手段に入力したので、アナログテレビジョン信号に基づく中間周波数帯のテレビジョン信号又はデジタルテレビジョン信号に基づく中間周波数帯のテレビジョン信号のいずれを送信する場合でも、正確なＡＧＣ電圧をえることができる。
【００３０】
また、本発明のＡＧＣ回路は、第一の帯域通過手段を第一のバンドパスフィルタで構成し、信号レベル制御手段を検波手段に接続するバイパス線路で第二の帯域通過手段を構成したので、簡単な構成で、アナログテレビジョン信号に基づく中間周波数帯のテレビジョン信号又はデジタルテレビジョン信号に基づく中間周波数帯のテレビジョン信号を検波手段に入力できる。
【００３１】
また、本発明のＡＧＣ回路は、第一の帯域通過手段を第一のバンドパスフィルタで構成し、中間周波数帯域を通過帯域とする第二のバンドパスフィルタで第二の帯域通過手段を構成したので、デジタルテレビジョン信号に基づく中間周波数帯のテレビジョン信号を検波する際には、中間周波数帯域外の信号による誤った検波電圧を検波することもない。
【００３２】
また、本発明のＡＧＣ回路は、帯域選択手段には中間周波数帯域のほぼ最高周波数をカットオフ周波数とするローパスフィルタと、音声中間周波数と映像中間周波数との間にカットオフ周波数を有する第一のハイパスフィルタと、中間周波数帯のほぼ最低周波数をカットオフ周波数とする第二のハイパスフィルタとを設け、信号レベル制御手段に前記アナログテレビジョン信号に基づく中間周波数帯の信号が入力されたときにはローパスフィルタと第一のハイパスフィルタとを直列に接続すると共に第一の帯域通過手段を構成し、デジタルテレビジョン信号の基づく中間周波数帯の信号が入力されたときにはローパスフィルタと第二のハイパスフィルタとを直列に接続すると共に第二の帯域通過手段を構成したので、二つのハイパスフィルタの切替のみで第一又は第二の帯域通過手段を構成できる。
【図面の簡単な説明】
【図１】本発明のＡＧＣ回路における第一の実施の形態の構成を示す回路図である。
【図２】本発明のＡＧＣ回路における第二の実施の形態の構成を示す回路図である。
【図３】本発明のＡＧＣ回路における第三の実施の形態の構成を示す回路図である。
【図４】従来のＡＧＣ回路の構成を示す回路図である。
【符号の説明】
１ レベル制御手段
２ 帯域選択手段
３ 第一のバンドパスフィルタ（第一の帯域通過手段）
４ バイパス線路（第二の帯域通過手段）
５、６ 切替手段
７ 中間周波増幅回路
８ 検波手段
８ａ、８ｂ 検波ダイオード
９ 直流増幅回路
１１ 第二のバンドパスフィルタ（第二の帯域通過手段）
１２ ローパスフィルタ
１３ 第一のハイパスフィルタ
１４ 第二のハイパスフィルタ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an AGC circuit used for a television signal transmitter or the like, and more particularly to an AGC circuit suitable for a television signal transmitter for a CATV system that transmits an analog television signal or a digital television signal.
[0002]
[Prior art]
FIG. 4 shows a conventional AGC circuit, in which a signal level control means 21 to which a television intermediate frequency band signal (referred to as an intermediate frequency signal) is input comprises a variable attenuation circuit or a variable gain amplification circuit, and its output level. Is controlled by the AGC voltage. As this intermediate frequency signal, an intermediate frequency signal for re-transmission of other received television signals or an intermediate frequency signal for a self-produced recorded program is used. The frequency of the video intermediate frequency signal (referred to as video intermediate frequency) is higher than the frequency of the audio intermediate frequency signal (referred to as audio intermediate frequency). For example, in the US specification, the audio intermediate frequency signal is 41.25 MHz and the video intermediate frequency signal is 45 .75 MHz.
[0003]
The intermediate frequency signal output from the signal level control means 21 is converted into a television signal of a predetermined channel by a frequency conversion circuit (not shown) and transmitted to a subscriber such as a CATV system.
[0004]
On the other hand, the intermediate frequency signal output from the signal level control means 21 is also input to the filter means 22 for extracting the video intermediate frequency signal. The filter means 22 is, for example, a bandpass filter such as a single tuning circuit that tunes to the video intermediate frequency, a high-pass filter having a cutoff frequency between the audio intermediate frequency and the video intermediate frequency, or a trap that attenuates the audio intermediate frequency. It is composed of a band-eliminated filter (band elimination filter) such as a circuit.
Accordingly, the filter means 22 removes the audio intermediate frequency signal and extracts only the video intermediate frequency signal.
[0005]
The extracted video intermediate frequency signal is amplified by the intermediate frequency amplifying circuit 23 and then detected by the detection means 24 to obtain a DC voltage (detection voltage) proportional to the level of the intermediate frequency signal. The detection means 24 is constituted by a known diode detection circuit composed of two diodes 24a and 24b.
[0006]
The detection voltage is amplified to a predetermined level by the DC amplification circuit 25, and the output voltage is input to the control terminal of the signal level control means 21 as an AGC voltage.
[0007]
In the above configuration, the detection voltage is output in proportion to the level of the input intermediate frequency signal. Therefore, when this voltage is input to the signal level control means 21 as an AGC voltage, it is output from the signal level control means 21. The level of the intermediate frequency signal is controlled to be substantially constant.
[0008]
[Problems to be solved by the invention]
However, the conventional AGC circuit corresponds to an existing analog television signal, and since the audio intermediate frequency band is attenuated by the filter means, if it is used as it is when transmitting a digital television signal, it will be output from the detection means. As a result, there is a problem that the detected AGC voltage is lowered and an accurate AGC operation is not performed.
[0009]
That is, in a digital television signal, there is no specific carrier wave modulated by a video signal and an audio signal, unlike an analog television signal, and an extremely large number of frequencies (several hundred to several numbers) in the entire intermediate frequency band. Thousand) components are digitally modulated by digital signals based on video and audio signals. Therefore, if the audio intermediate frequency band is attenuated, the power of the digital television signal input to the detection means is reduced by that amount, and as a result, the detection voltage is reduced.
[0010]
Therefore, an object of the AGC circuit of the present invention is to ensure that AGC is applied both when an analog television signal is transmitted and when a digital television signal is transmitted.
[0011]
As means for solving the above-described problems, the AGC circuit of the present invention receives an intermediate frequency band television signal based on an analog television signal or a digital television signal, and outputs the intermediate frequency band television signal by an AGC voltage. A signal level control means for changing the output level, and detecting a television signal in the intermediate frequency band outputted from the signal level control means to output a DC voltage, and using the DC voltage as the AGC voltage, the signal level A detection means for inputting to the control means, and prevents a signal of an audio intermediate frequency in the intermediate frequency band of the reception channel from passing between the output end of the signal level control means and the input end of the detection means. a first band-pass means for passing a signal of a video intermediate frequency Te, at least in said receiving channel Band selection means comprising second band passing means for passing all signals in the frequency band is provided, and when a television signal in an intermediate frequency band based on the analog television signal is input to the signal level control means, The intermediate frequency band television signal is input to the detection means via the first band passing means, and the second band pass when the intermediate frequency band television signal based on the digital television signal is input. The intermediate frequency band television signal is input to the detection means via the means.
[0012]
In the AGC circuit of the present invention, the first band pass means is constituted by a first band pass filter, and the second band pass means is constituted by a bypass line connecting the signal level control means to the detection means. Configured.
[0013]
In the AGC circuit of the present invention, the first band pass means is constituted by a first band pass filter, and the second band pass means is constituted by a second band pass filter having the intermediate frequency band as a pass band. Configured.
[0014]
In the AGC circuit of the present invention, the band selecting means has a low-pass filter having a cutoff frequency that is substantially the highest frequency of the intermediate frequency band, and a cutoff frequency between the audio intermediate frequency and the video intermediate frequency. A first high-pass filter having a first high-pass filter and a second high-pass filter having a cut-off frequency at a substantially lowest frequency of the intermediate frequency band, and the signal level control means receives a signal in the intermediate frequency band based on the analog television signal. When input, the low-pass filter and the first high-pass filter are connected in series and constitute the first band pass means, and when an intermediate frequency band signal based on the digital television signal is input, A low-pass filter and the second high-pass filter are connected in series and the second To constitute a band-pass means.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The AGC circuit of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of an AGC circuit according to the present invention. A television signal in an intermediate frequency band (referred to as an intermediate frequency signal) based on an analog television signal or a digital television signal is signal level controlled. Input to means 1. The signal level control means 1 is composed of a variable attenuation circuit or a variable gain amplifier circuit, and its output level is controlled by the AGC voltage.
[0016]
Here, as the intermediate frequency signal, a signal based on a television signal of another received system is used, or a signal based on a recorded self-produced program is used, but when based on an analog television signal, The frequency of the video intermediate frequency signal (referred to as video intermediate frequency) is higher than the frequency of the audio intermediate frequency signal (referred to as audio intermediate frequency). For example, in the US specification, the audio intermediate frequency signal is 41.25 MHz, and the video intermediate frequency signal is 45. 75 MHz.
[0017]
On the other hand, in the case of an intermediate frequency signal based on a digital television signal, an extremely large number of frequencies (several hundreds to thousands) in the entire intermediate frequency band are digitally modulated by a digital signal based on a video signal and an audio signal. Therefore, there is no specific video carrier and audio carrier.
[0018]
The intermediate frequency signal output from the signal level control means 1 is converted into a television signal of a predetermined channel by a frequency conversion circuit (not shown) and transmitted to a subscriber such as a CATV system.
[0019]
On the other hand, the intermediate frequency signal output from the signal level control unit 1 is input to the band selection unit 2. The band selecting means 2 includes a first band pass filter 3 that is a first band passing means that passes the video intermediate frequency in the intermediate frequency band of the reception channel and blocks the audio intermediate frequency, and the entire band of at least the intermediate frequency band. The bypass line 4 that is the second band passing means that passes through and the switching means 5 and 6 are selected, and either the first bandpass filter 3 or the bypass line 4 is selected by the switching means 5 or 6.
[0020]
The intermediate frequency signal is input to the intermediate frequency amplifier circuit 7 via either the first bandpass filter 3 or the bypass line 4. The amplified intermediate frequency signal is detected by the detection means 8 and outputs a DC voltage (detection voltage). The detection voltage is proportional to the level of the intermediate frequency signal input to the signal level control means 1. The detection means 8 is constituted by a known diode detection circuit or the like including two detection diodes 8a and 8b.
[0021]
The detection voltage is amplified to a predetermined level by the DC amplification circuit 9 and the output voltage is input to the control end of the signal level control means 1 as an AGC voltage. As a result, the level of the intermediate frequency signal output from the signal level control means 1 is controlled to be substantially constant.
[0022]
In the above configuration, the band selection unit 2 selects the first bandpass filter 3 if the intermediate frequency signal input to the signal level control unit 1 is based on an analog television signal. Then, a detection voltage based only on the video intermediate frequency signal is obtained from the detection means 8. As a result, the signal level control means 1 performs the AGC operation based on the video signal.
[0023]
On the other hand, if the intermediate frequency signal input to the signal level control means 1 is based on a digital television signal, the bypass line 4 is selected. As a result, since the signal in the entire intermediate frequency band is detected, the detection voltage does not decrease. And since the bypass line 4 is used as a 2nd zone passage means, a structure becomes simple.
[0024]
FIG. 2 shows a second embodiment of the AGC circuit of the present invention, in which a second band pass filter 11 is provided instead of the bypass line 4 shown in FIG. The second band pass filter 11 is configured so that the entire intermediate frequency band is the pass band. Therefore, if the intermediate frequency signal input to the signal level control means 1 is based on a digital television signal, the second band pass filter 11 is selected and the signal in the entire intermediate frequency band is sent to the detection means 8. Entered. And since the 2nd band pass filter 11 is used as a 2nd zone passage means, the false detection voltage by the signal outside an intermediate frequency band is not detected.
[0025]
FIG. 3 shows a third embodiment of the AGC circuit of the present invention. The band selecting means 2 has a low-pass filter 12, a first high-pass filter 13, and a second high-pass filter 14. The first high-pass filter 13 or the second high-pass filter 14 is connected in series by the switching means 5 and 6.
[0026]
The low-pass filter 12 has a cutoff frequency at substantially the highest frequency in the intermediate frequency band, the first high-pass filter 13 has a cutoff frequency between the audio intermediate frequency and the video intermediate frequency in the intermediate frequency band, and The second high-pass filter 14 has a cut-off frequency at approximately the lowest frequency in the intermediate frequency region.
[0027]
When an intermediate frequency band signal based on an analog television signal is input to the signal level control means, the first high-pass filter 13 is selected to connect the low-pass filter and the first high-pass filter in series and And a second high-pass filter 14 is selected to connect the low-pass filter and the second high-pass filter in series when an intermediate frequency band signal based on the digital television signal is input. The second band passing means is configured.
[0028]
As a result, if the intermediate frequency signal input to the signal level control means 1 is based on an analog television signal, only the video intermediate frequency signal is input to the detection means 8.
On the other hand, if the intermediate frequency signal input to the signal level control means 1 is based on a digital television signal, a signal in the entire intermediate frequency band is input to the detection means 8 and an accurate detection voltage is obtained.
[0029]
【The invention's effect】
As described above, AGC circuit of the present invention, between the input terminal of the output terminal and the detection means of the signal level control means, the image and prevents the passage of sound intermediate frequency signal in the intermediate frequency band of the receiving channel a first band-pass means for passing the intermediate frequency signal, provided band selection means comprising a second band-pass means for passing all of the signal at least an intermediate frequency band of said reception channel, the signal level control means When an intermediate frequency band television signal based on the analog television signal is input to the digital television, the intermediate frequency band television signal is input to the detection means via the first band passing means. When a television signal of an intermediate frequency band based on the signal is input, the intermediate frequency band of the intermediate frequency band is passed through the second band passing means. Since the revision signal is input to the detection means, an accurate AGC voltage can be obtained regardless of whether an intermediate frequency band television signal based on an analog television signal or an intermediate frequency band television signal based on a digital television signal is transmitted. You can
[0030]
In the AGC circuit of the present invention, the first band pass means is constituted by the first band pass filter, and the second band pass means is constituted by the bypass line connecting the signal level control means to the detection means. With a simple configuration, an intermediate frequency band television signal based on an analog television signal or an intermediate frequency band television signal based on a digital television signal can be input to the detection means.
[0031]
In the AGC circuit of the present invention, the first band pass means is constituted by the first band pass filter, and the second band pass means is constituted by the second band pass filter having the intermediate frequency band as the pass band. Therefore, when detecting an intermediate frequency band television signal based on a digital television signal, an erroneous detection voltage due to a signal outside the intermediate frequency band is not detected.
[0032]
In the AGC circuit of the present invention, the band selecting means includes a low-pass filter having a cutoff frequency that is substantially the highest frequency in the intermediate frequency band, and a first filter having a cutoff frequency between the audio intermediate frequency and the video intermediate frequency. A high-pass filter and a second high-pass filter having a cut-off frequency at a substantially lowest frequency in the intermediate frequency band, and a low-pass filter when a signal in the intermediate frequency band based on the analog television signal is input to the signal level control means And a first high-pass filter are connected in series and constitute a first band-pass means. When an intermediate frequency band signal based on a digital television signal is input, a low-pass filter and a second high-pass filter are connected in series. And the second bandpass means is configured so that two high-pass filters Switching only possible configuration of the first or second band-pass means.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a first embodiment in an AGC circuit of the present invention.
FIG. 2 is a circuit diagram showing a configuration of a second embodiment of the AGC circuit of the present invention.
FIG. 3 is a circuit diagram showing a configuration of a third embodiment of the AGC circuit of the present invention.
FIG. 4 is a circuit diagram showing a configuration of a conventional AGC circuit.
[Explanation of symbols]
1 Level control means 2 Band selection means 3 First band pass filter (first band pass means)
4 Bypass line (second band pass means)
5, 6 Switching means 7 Intermediate frequency amplification circuit 8 Detection means 8a, 8b Detection diode 9 DC amplification circuit 11 Second bandpass filter (second bandpass means)
12 Low-pass filter 13 First high-pass filter 14 Second high-pass filter

Claims (4)

アナログテレビジョン信号又はデジタルテレビジョン信号に基づく中間周波数帯のテレビジョン信号が入力され、ＡＧＣ電圧によって前記中間周波数帯のテレビジョン信号のレベルを変えて出力する信号レベル制御手段と、前記信号レベル制御手段から出力される前記中間周波数帯のテレビジョン信号を検波して直流電圧を出力すると共に前記直流電圧を前記ＡＧＣ電圧として前記信号レベル制御手段に入力する検波手段とを備え、前記信号レベル制御手段の出力端と前記検波手段の入力端との間には、受信チャンネルの前記中間周波数帯における音声中間周波数の信号の通過を阻止して映像中間周波数の信号を通過する第一の帯域通過手段と、少なくとも前記受信チャンネルの中間周波数帯における全ての信号を通過する第二の帯域通過手段とからなる帯域選択手段を設け、前記信号レベル制御手段に前記アナログテレビジョン信号に基づく中間周波数帯のテレビジョン信号が入力されたときには前記第一の帯域通過手段を介して前記中間周波数帯のテレビジョン信号を前記検波手段に入力し、前記デジタルテレビジョン信号に基づく中間周波数帯のテレビジョン信号が入力されたときには前記第二の帯域通過手段を介して前記中間周波数帯のテレビジョン信号を前記検波手段に入力したことを特徴とするＡＧＣ回路。A signal level control means for inputting a television signal in an intermediate frequency band based on an analog television signal or a digital television signal and changing the level of the television signal in the intermediate frequency band according to an AGC voltage, and the signal level control Detecting means for detecting the television signal in the intermediate frequency band outputted from the means and outputting a DC voltage, and inputting the DC voltage as the AGC voltage to the signal level control means, and the signal level control means A first band pass means for preventing the passage of the audio intermediate frequency signal in the intermediate frequency band of the reception channel and passing the video intermediate frequency signal between the output end of the detection means and the input end of the detection means. a second band-pass hand which passes all signals in at least the intermediate frequency band of the receiving channel And when the intermediate frequency band television signal based on the analog television signal is input to the signal level control means, the intermediate frequency band television is set via the first band passing means. The intermediate frequency band is input to the detection means, and when the intermediate frequency band television signal based on the digital television signal is input, the intermediate frequency band television signal is detected via the second band passing means. An AGC circuit characterized by being input to the means. 前記第一の帯域通過手段を第一のバンドパスフィルタで構成し、前記信号レベル制御手段を前記検波手段に接続するバイパス線路で前記第二の帯域通過手段を構成したことを特徴とする請求項１記載のＡＧＣ回路。  The first band-pass means is constituted by a first band-pass filter, and the second band-pass means is constituted by a bypass line connecting the signal level control means to the detection means. 1. The AGC circuit according to 1. 前記第一の帯域通過手段を第一のバンドパスフィルタで構成し、前記中間周波数帯域を通過帯域とする第二のバンドパスフィルタで前記第二の帯域通過手段を構成したことを特徴とする請求項１記載のＡＧＣ回路。  The first band pass means is constituted by a first band pass filter, and the second band pass means is constituted by a second band pass filter having the intermediate frequency band as a pass band. Item 2. The AGC circuit according to Item 1. 前記帯域選択手段には前記中間周波数帯域のほぼ最高周波数をカットオフ周波数とするローパスフィルタと、前記音声中間周波数と前記映像中間周波数との間にカットオフ周波数を有する第一のハイパスフィルタと、前記中間周波数帯のほぼ最低周波数をカットオフ周波数とする第二のハイパスフィルタとを設け、前記信号レベル制御手段に前記アナログテレビジョン信号に基づく中間周波数帯の信号が入力されたときには前記ローパスフィルタと前記第一のハイパスフィルタとを直列に接続すると共に前記第一の帯域通過手段を構成し、前記デジタルテレビジョン信号の基づく中間周波数帯の信号が入力されたときには前記ローパスフィルタと前記第二のハイパスフィルタとを直列に接続すると共に前記第二の帯域通過手段を構成したことを特徴とする請求項１記載のＡＧＣ回路。  The band selection means includes a low-pass filter having a cutoff frequency that is substantially the highest frequency of the intermediate frequency band, a first high-pass filter having a cutoff frequency between the audio intermediate frequency and the video intermediate frequency, A second high-pass filter having a cutoff frequency that is substantially the lowest frequency of the intermediate frequency band, and when the signal of the intermediate frequency band based on the analog television signal is input to the signal level control means, the low-pass filter and the A first high-pass filter is connected in series and constitutes the first band-pass means. When a signal in an intermediate frequency band based on the digital television signal is input, the low-pass filter and the second high-pass filter Are connected in series and the second band pass means is configured. AGC circuit according to claim 1, wherein.
JP31635699A 1999-11-08 1999-11-08 AGC circuit Expired - Fee Related JP3668655B2 (en)

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