JP2004312077A

JP2004312077A - Fm tuner

Info

Publication number: JP2004312077A
Application number: JP2003098865A
Authority: JP
Inventors: Yutaka Matsumoto; 豊松本
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2003-04-02
Filing date: 2003-04-02
Publication date: 2004-11-04

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FM tuner capable of more efficiently receiving a desired wave by controlling a bandwidth of its IF filter. <P>SOLUTION: An IF limiter 2 eliminates noise from an FM signal passing through the IF filter 1 and an FM detector 3 outputs an FM detection signal. An adjacent disturbance detector 4 receiving the FM detection signal detects a level of the noise of an adjacent disturbing wave. An electric field detector 6 detects a level of the FM signal from an output of the IF limiter amplifier 2, and a weak electric field detector 7 receiving the level of the FM signal judges whether or not the FM signal results from a weak electric field. A controller 5 receiving output results from the adjacent disturbance detector 4 and the weak electric field detector 7 generates a control signal of the IF filter 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、ＦＭ（ＦｒｅｑｕｅｎｃｙＭｏｄｕｌａｔｉｏｎ）チューナに関し、特にカーオーディオ等の移動体受信に使用されるＦＭチューナに関する。
【０００２】
【従来の技術】
ＦＭチューナの構成を図７に示す。以下、図面に従って説明する。
【０００３】
ＩＦ（ＩｎｔｅｒｍｅｄｉａｔｅＦｒｅｑｕｅｎｃｙ）フィルタ１０１は、中間周波数（例えば、４５０ｋＨｚ）を中心として、−３デシベル帯域幅を約３０ｋＨｚ〜約２００ｋＨｚまで可変できるものである。
【０００４】
ここで帯域幅の可変とは、２つ以上の固定した帯域幅を予め設定しておいて設定した帯域幅に切り替えるものと、帯域幅は予め固定せずにフレキシブルに帯域幅を変えることができるものの双方の意味を有している。
【０００５】
ＩＦフィルタ１０１を通過したＦＭ信号は、ＩＦリミッタアンプ１０２に供給される。ＩＦフィルタ１０１を通過したＦＭ信号は、ＩＦリミッタアンプ１０２に供給される。ＩＦリミッタアンプ１０２は、ＦＭ信号の振幅を増幅して矩形波とし、ＦＭ信号にのったノイズを除去している。
【０００６】
ＦＭ検波器１０３は、ＩＦリミッタアンプ１０２からのＦＭ信号を検波し、ＦＭ検波出力（音声信号）として出力する。
【０００７】
ＦＭ検波出力は、隣接妨害検出器１０４に供給される。隣接妨害検出器１０４は、ＦＭ検波出力の帯域における隣接妨害波のノイズ（高域に位置する）のレベルと所定のレベルとの差を生成する。
【０００８】
このレベル差の信号をコントローラ１０５に供給する。コントローラ１０５は、隣接妨害検出器１０４からのレベル差が大きいとＩＦフィルタ１０１の帯域幅を広くして希望波を広く受信することができる。逆にレベル差が小さいと希望波と隣接妨害波とが接近しているので、ＩＦフィルタ１０１の帯域幅を狭くして隣接妨害波を遮断している。
【０００９】
同様に、図８に示すように隣接妨害検出器１０４とＩＦリミッタアンプ１０２との間に電界検出器１０６を挿入しても隣接妨害波を検出できる。電界検出器１０６は、ＩＦリミッタアンプ１０２からＦＭ信号を検出する。隣接妨害検出器１０４は、電界検出器１０６からの中間周波数帯域での隣接妨害波の搬送波のレベルと所定のレベルとの差を生成する。
【００１０】
このレベル差の信号をコントローラ１０５に供給する。コントローラ１０５は、隣接妨害検出器１０４からのレベル差が大きいとＩＦフィルタ１０１の帯域幅を広くして希望波を広く受信することができる。逆にレベル差が小さいと希望波と隣接妨害波とが接近しているので、ＩＦフィルタ１０１の帯域幅を狭くして隣接妨害波を遮断している（例えば、特許文献１参照。）。
【００１１】
【特許文献１】
特許第２８２５３８９号公報
【００１２】
【発明が解決しようとする課題】
しかし、前述した従来のＦＭチューナは、ＦＭ検波出力の帯域における隣接妨害波のノイズ、中間周波数帯域での隣接妨害波の搬送レベル等を所定値に抑えるため、ＩＦフィルタ１０１の帯域幅を制御している。このため、隣接妨害波と希望波の帯域が接近していたり、希望波の変調度が大きいような場合にはＩＦフィルタ１０１の帯域幅が過度に狭くなってしまい、希望波の変調度に対する欠損が大きくなり、ＦＭ検波特性（全高調波歪等）が悪化する。
【００１３】
更に、隣接妨害検出器の出力は、ＦＭ検波出力の帯域における隣接妨害波のノイズレベル、または中間周波数帯域での隣接妨害波を検出したものであるため、リップルを生じてしまう。このため、隣接妨害時におけるＩＦフィルタ１０１の安定な帯域幅の可変は望めない。
【００１４】
そこで本発明は、希望波を受信中はＩＦフィルタの帯域幅を過度に狭くすることのないＦＭチューナを提供することを目的とする。
【００１５】
更に本発明は、隣接妨害時における中間周波数フィルタの安定な帯域の可変を可能にするＦＭチューナを提供することを目的とする。
【００１６】
【課題を解決するための手段】
上記課題を解決するために本発明の一態様によれば、ＦＭ信号が入力される、帯域幅を可変可能な中間処理フィルタと、この中間処理フィルタからのＦＭ信号の振幅を増幅し、前記ＦＭ信号を矩形波とする中間周波数リミッタアンプと、この中間周波数リミッタアンプからのＦＭ信号をＦＭ検波するＦＭ検波器と、このＦＭ検波器から出力されたＦＭ検波出力より、前記ＦＭ検波出力の帯域における隣接妨害波のノイズのレベルと所定のレベルとのレベル差を生成する隣接妨害検出器と、前記中間周波数フィルタの出力端と前記ＦＭ検波器の入力端との間から供給されるＦＭ信号のレベルを検出する電界検出器と、この電界検出器で検出されたＦＭ信号の電界検出量と所定のレベルとのレベル差を生成する弱電界検出器と、前記隣接妨害検出器で生成されたレベル差及び前記弱電界検出器で生成されたレベル差が供給されるコントローラとを備え、前記コントローラは、前記隣接妨害検出器で生成されたレベル差及び前記弱電界検出器で生成されたレベル差に基づき、前記中間周波数フィルタの帯域幅を制御する制御信号を生成し、かつ前記制御信号に対し所定の時定数を備えたことを特徴とするＦＭチューナが提供される。
【００１７】
また本発明の他の態様によれば、ＦＭ信号が入力される、帯域幅を可変可能な中間周波数フィルタと、この中間周波数フィルタからのＦＭ信号の振幅を増幅し、前記ＦＭ信号を矩形波とする中間周波数リミッタアンプと、この中間周波数リミッタアンプからのＦＭ信号をＦＭ検波するＦＭ検波器と、前記中間周波数フィルタの出力端と前記ＦＭ検波器の入力端との間から供給されるＦＭ信号のレベルを検出する電界検出器と、この電界検出器で検出されたＦＭ信号の電界検出量と所定のレベルとのレベル差を生成する弱電界検出器と、前記電界検出器からの中間周波数帯域での隣接妨害波の搬送レベルと所定のレベルとのレベル差を生成する隣接妨害検出器と、前記隣接妨害検出器で生成されたレベル差及び前記弱電界検出器で生成されたレベル差が供給されるコントローラとを備え、前記コントローラは、前記隣接妨害検出器で生成されたレベル差及び前記弱電界検出器で生成されたレベル差に基づき、前記中間周波数フィルタの帯域幅を制御する制御信号を生成し、かつ前記制御信号に対し所定の時定数を備えたことを特徴とするＦＭチューナが提供される。
【００１８】
また本発明の他の態様によれば、ＦＭ信号が入力される、帯域幅を可変可能な中間周波数フィルタと、この中間周波数フィルタからのＦＭ信号の振幅を増幅し、前記ＦＭ信号を矩形波とする中間周波数リミッタアンプと、この中間周波数リミッタアンプからのＦＭ信号をＦＭ検波するＦＭ検波器と、このＦＭ検波器から出力されたＦＭ検波出力より、前記ＦＭ検波出力の帯域における隣接妨害波のノイズのレベルとのレベル差を生成する隣接妨害検出器と、前記ＦＭ検波出力から希望波の音声レベルを検出する変調度検出器と、前記中間周波数フィルタの出力端と前記ＦＭ検波器の入力端との間から供給されるＦＭ信号のレベルを検出する電界検出器と、この電界検出器で検出されたＦＭ信号の電界検出量と所定のレベルとのレベル差を生成する弱電界検出器と、前記隣接妨害検出器で生成されたレベル差及び前記変調度検出器で生成された音声レベル及び前記弱電界検出器で生成されたレベル差が供給されるコントローラとを備え、前記隣接妨害検出器で生成されたレベル差及び前記音声レベル及び前記弱電界検出器で生成されたレベル差に基づき、前記中間周波数フィルタの帯域幅を制御する制御信号を生成し、かつ前記制御信号に対し所定の時定数を備えたことを特徴とするＦＭチューナが提供される。
【００１９】
【発明の実施の形態】
本発明の実施形態について図を参照しながら説明する。
【００２０】
［第１の実施形態］図１は本発明の第１の実施形態に係るＦＭチューナの構成図である。
【００２１】
ＩＦフィルタ１は、中間周波数（例えば、４５０ｋＨｚ）を中心にして設定された帯域幅のＦＭ信号を通過させる。帯域幅は、−３デシベル帯域幅を約３０ｋＨｚ〜約２００ｋＨｚまで可変することができる。
【００２２】
ここで帯域幅の可変とは、２つ以上の固定した帯域幅を予め設定しておいて設定した帯域幅に切り替えるものと、帯域幅は予め固定せずにフレキシブルに帯域幅を変えることができるものの双方の意味を有している。
【００２３】
ＩＦフィルタ１を通過したＦＭ信号は、ＩＦリミッタアンプ２に供給される。ＩＦリミッタアンプ２は、ＦＭ信号の振幅を増幅して矩形波とし、ＦＭ信号にのったノイズを除去している。
【００２４】
ＩＦリミッタアンプ２で増幅され矩形波のＦＭ信号は、ＦＭ検波器３に入力される。ＦＭ検波器３は、ＩＦリミッタアンプ２で形成された矩形波を検知してＦＭ検波出力（音声信号）を出力する。
【００２５】
ＦＭ検波出力は、隣接妨害検出器４に入力される。隣接妨害検出器４は、ＦＭ信号の希望波に隣接する妨害波を検出している。
【００２６】
隣接妨害検出器４は例えば図２のように構成されている。ＦＭ検波器３からのＦＭ検波出力を第１のバンドパスフィルタ４１と第２のバンドパスフィルタ４２に入力する。第１のバンドパスフィルタ４１は高域側の隣接妨害波の中心周波数ｆ０を持つフィルタである。また、第２のバンドパスフィルタ４２は低域側の隣接妨害波の中心周波数ｆ０を持つフィルタである。
【００２７】
第１及び第２のバンドパスフィルタ４１，４２を通過した信号を合成回路４３に入力し、これらの信号を合成する。合成回路４３では、例えば加算又はＯＲ演算される。検出回路４４は、合成回路４３からの出力レベルと所定のレベルとの差を生成する。このレベル差をコントローラ５に供給する。
【００２８】
検出した妨害波の情報をコントローラ５に入力する。このコントローラ５は、ＦＭチューナが希望波以外の、特に隣接する妨害波を排除するようにＩＦフィルタ１を制御する回路である。
【００２９】
また、ＩＦリミッタアンプ２は電界検出器６にも接続されている。ＩＦリミッタアンプ２は、数段のバッファ回路が直列に繋げた回路から構成されている。電界検出器６は、ＩＦリミッタアンプ２の複数のバッファ回路の出力をそれぞれ入力信号としており、ＦＭ信号の信号強度を検出している。
【００３０】
電界検出器６の出力信号は、弱電界検出器７に入力される。弱電界検出器７は、ＦＭ信号の信号強度を監視して、所定の電界以下（弱電界）を検出する検出器である。弱電界検出器７の出力信号もコントローラ５に入力する。
【００３１】
コントローラ５では、隣接妨害検出器４から入力されたレベル差が大きい場合、すなわち希望波と隣接妨害波が接近していない場合は、ＩＦフィルタ１の帯域幅を広くするように制御する。他方、隣接妨害検出器４から入力されたレベル差が小さい場合、すなわち希望波と隣接妨害波が接近している場合は、ＩＦフィルタ１の帯域幅を狭くするように制御する。
【００３２】
また、コントローラ５は、弱電界検出器７から入力されたＦＭ信号の信号強度が小さい場合、すなわち希望波が弱電界の場合は、ＩＦフィルタ１の帯域幅を広くするように制御する。
【００３３】
通常、弱電界の場合はＦＭ検波出力又は電界検出出力のノイズによるＩＦフィルタ１の帯域制御誤動作を防ぐため、予め隣接妨害検出器４の検出感度の設定を低くしなくてはいけない。そのため隣接妨害検出器４が本来の隣接妨害波を検出することができず、例え隣接妨害波が希望波と比較的離れていてもＩＦフィルタ１の帯域幅を広くすることができない。本来帯域幅を広げられるＩＦフィルタ１も帯域幅が狭くなってしまう。
【００３４】
しかし、弱電界検出器７によって弱電界時にはＩＦフィルタ１の帯域幅を広くすることによって、隣接妨害検出器４の検出感度を向上させて隣接妨害波を有効に検出してＩＦフィルタ１を調整することができる。
【００３５】
また、本実施形態の隣接妨害検出器４は図３に示すように電界検出器６とコントローラ５間に挿入しても隣接妨害波を検出でき、本発明の効果を得ることができる。
【００３６】
［第２の実施形態］次に本発明の第２の実施形態に係るＦＭチューナの構成図を図４に示す。
【００３７】
ＩＦフィルタ１、ＩＦリミッタアンプ２、ＦＭ検波器３、隣接妨害検出器４、コントローラ５、電界検出器６及び弱電界検出器７は、第１の実施形態において説明した図１のＦＭチューナの構成と同様であるので、説明を省略する。
【００３８】
図４に示すＦＭチューナは、図１に示すＦＭチューナのＦＭ検波器３とコントローラ５間に変調度検出器８を挿入した構成である。
【００３９】
変調度検出器８は、ＦＭ検波器３のＦＭ検波出力から希望波の音声レベルを検出する。希望波の変調度（希望波の中心周波数ｆ０からの周波数変調）が大きいほど、大きな音声レベルの信号となる。この音声レベルをコントローラ５に供給する。ここで、変調度検出器８から出力された音声レベルは、検波出力の帯域における隣接妨害波のノイズ、中間周波数帯域の搬送レベル等は基本的に含まれていない。
【００４０】
コントローラ５には、隣接妨害検出器４、弱電界検出器７及び変調度検出器８で検出された信号が入力されている。
【００４１】
隣接妨害検出器４から入力されたレベル差が大きいほどＩＦフィルタ１の帯域幅を広くするように制御し、レベル差が小さいほどＩＦフィルタ１の帯域幅を狭くするように制御する。
【００４２】
また、弱電界検出器７から入力されたＦＭ信号の信号強度が小さい場合はＩＦフィルタ１の帯域幅を広くするように制御する。
【００４３】
更に、変調度検出器８から入力された希望波の変調度が大きい場合、すなわち大きな音声レベルの場合は、ＩＦフィルタ１の帯域幅を大きくするように制御する。希望波の変調度に対する欠損を極力抑え、ＦＭ検波特性（全高調波歪等）を高めることができる。
【００４４】
このように、受信したＦＭ信号を各々の検出器で得た情報からコントローラ５を制御して、最適なＩＦフィルタ１の帯域幅を決定することができる。
【００４５】
なお、第１の実施形態と同様に隣接妨害検出器４は電界検出器６とコントローラ５間に挿入してもよい。
【００４６】
［第３の実施形態］次に本発明の第３の実施形態に係るＦＭチューナの構成図を図５に示す。
【００４７】
ＩＦフィルタ１、ＩＦリミッタアンプ２、ＦＭ検波器３、隣接妨害検出器４、コントローラ５、電界検出器６及び弱電界検出器７は、第１の実施形態において説明した図１のＦＭチューナの構成と同様であるので、説明を省略する。
【００４８】
図５に示すＦＭチューナは、ＦＭ検波器３と隣接妨害検出器間４にミュート回路９を挿入した構成である。このミュート回路９は、電界検出器６の出力によって制御されている。電界検出器６で弱電界と判断された場合、ＦＭ検波出力はミュート回路９によってＦＭ検波出力をミューティングする。
【００４９】
弱電界時におけるＦＭ検波出力のノイズ増大による聴感品位の低下を緩和するようにミュート回路９によってＦＭ検波出力は制御され、同時にＦＭ検波出力のノイズ増大による隣接妨害検出器４の誤動作を各電界強度でも避けることができる。したがって、弱電界時でも予め隣接妨害検出器４の検出感度の設定を低くする必要がなく、隣接妨害検出器４の検出感度を向上させて隣接妨害波を有効に検出してＩＦフィルタ１を調整することができる。
【００５０】
コントローラ５には、隣接妨害検出器４及び弱電界検出器７で検出された信号が入力されている。
【００５１】
隣接妨害検出器４から入力されたレベル差が大きいほどＩＦフィルタ１の帯域幅を大きくするように制御し、レベル差が小さいほどＩＦフィルタ１の帯域幅を狭くするように制御する。
【００５２】
また、弱電界検出器７から入力されたＦＭ信号の信号強度が小さい場合はＩＦフィルタ１の帯域幅を広くするように制御する。
【００５３】
このように、受信したＦＭ信号を各々の検出器で得た情報からコントローラ５を制御して、最適なＩＦフィルタ１の帯域幅を決定することができる。
【００５４】
なお、第１の実施形態と同様に隣接妨害検出器４は電界検出器６とコントローラ５間に挿入してもよい。
【００５５】
［第４の実施形態］次に本発明の第４の実施形態に係るＦＭチューナの構成図を図６に示す。
【００５６】
ＩＦフィルタ１、ＩＦリミッタアンプ２、ＦＭ検波器３、隣接妨害検出器４、コントローラ５、電界検出器６、弱電界検出器７及びミュート回路９は、第３の実施形態において説明した図５のＦＭチューナの構成と同様であるので、説明を省略する。
【００５７】
図６に示すＦＭチューナは、図５に示すＦＭチューナのＦＭ検波器３とコントローラ５間に変調度検出器８を挿入した構成である。変調度検出器８は、前記第２の実施形態で説明した変調度検出器８と同様なので説明を省略する。
【００５８】
コントローラ５には、隣接妨害検出器４、弱電界検出器７及び変調度検出器８で検出された信号が入力されている。
【００５９】
隣接妨害検出器４から入力されたレベル差が大きいほどＩＦフィルタ１の帯域幅を広くするように制御し、レベル差が小さいほどＩＦフィルタ１の帯域幅を狭くするように制御する。
【００６０】
また、弱電界検出器７から入力されたＦＭ信号の信号強度が小さい場合はＩＦフィルタ１の帯域幅を広くするように制御する。
【００６１】
更に、変調度検出器８から入力された希望波の変調度が大きい場合、すなわち大きな音声レベルの場合は、ＩＦフィルタ１の帯域幅を大きくするように制御する。
【００６２】
このように、受信したＦＭ信号を各々の検出器で得た情報からコントローラ５を制御して、最適なＩＦフィルタ１の帯域幅を決定することができる。
【００６３】
なお、第１の実施形態と同様に隣接妨害検出器４は電界検出器６とコントローラ５間に挿入してもよい。
【００６４】
なお、前述した本発明のＦＭチューナは回路発振を防ぐためＩＦフィルタ１制御には所定の時定数を持たせている。例えば、コントローラ５に積分器を設ければよい。
【００６５】
【発明の効果】
以上詳述したように本発明は、希望波を受信中はＩＦフィルタの帯域幅を過度に狭くすることがなく、隣接妨害時における中間周波数フィルタの安定な帯域の可変を可能にするＦＭチューナを提供することができる。
【図面の簡単な説明】
【図１】本発明の第１の実施形態に係るＦＭチューナ回路の構成図である。
【図２】図１の隣接妨害検出器の一例を表わす構成図である。
【図３】本発明の第１の実施形態に係るＦＭチューナ回路の変形例を表わす構成図である。
【図４】本発明の第２の実施形態に係るＦＭチューナ回路の構成図である。
【図５】本発明の第３の実施形態に係るＦＭチューナ回路の構成図である。
【図６】本発明の第４の実施形態に係るＦＭチューナ回路の構成図である。
【図７】従来技術のＦＭチューナ回路の構成図である。
【図８】従来技術のＦＭチューナ回路の構成図である。
【符号の説明】
１・・・ＩＦフィルタ
２・・・ＩＦリミッタアンプ
３・・・ＦＭ検波器
４・・・隣接妨害検出器
４１・・・第１のバンドパスフィルタ
４２・・・第２のバンドパスフィルタ
４３・・・合成回路
４４・・・検出回路
５・・・コントローラ
６・・・電界検出器
７・・・弱電界検出器
８・・・変調度検出器
９・・・ミュート回路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an FM (Frequency Modulation) tuner, and more particularly to an FM tuner used for receiving a mobile unit such as a car audio.
[0002]
[Prior art]
FIG. 7 shows the configuration of the FM tuner. Hereinafter, description will be made with reference to the drawings.
[0003]
The IF (Intermediate Frequency) filter 101 can change the −3 dB bandwidth from about 30 kHz to about 200 kHz around an intermediate frequency (for example, 450 kHz).
[0004]
Here, the variable bandwidth means that two or more fixed bandwidths are set in advance and switched to the set bandwidth, and the bandwidth can be changed flexibly without fixing the bandwidth in advance. Things have both meanings.
[0005]
The FM signal that has passed through the IF filter 101 is supplied to an IF limiter amplifier 102. The FM signal that has passed through the IF filter 101 is supplied to an IF limiter amplifier 102. The IF limiter amplifier 102 amplifies the amplitude of the FM signal to form a rectangular wave, and removes noise on the FM signal.
[0006]
The FM detector 103 detects the FM signal from the IF limiter amplifier 102 and outputs it as an FM detection output (audio signal).
[0007]
The FM detection output is supplied to the adjacent interference detector 104. The adjacent interference detector 104 generates a difference between the level of noise (located at a high frequency) of the adjacent interference wave in the band of the FM detection output and a predetermined level.
[0008]
The signal of the level difference is supplied to the controller 105. When the level difference from the adjacent interference detector 104 is large, the controller 105 can widen the bandwidth of the IF filter 101 and widely receive a desired wave. Conversely, if the level difference is small, the desired wave and the adjacent interference wave are close to each other, so that the bandwidth of the IF filter 101 is narrowed to block the adjacent interference wave.
[0009]
Similarly, as shown in FIG. 8, even if an electric field detector 106 is inserted between the adjacent interference detector 104 and the IF limiter amplifier 102, the adjacent interference wave can be detected. The electric field detector 106 detects an FM signal from the IF limiter amplifier 102. The adjacent interference detector 104 generates a difference between the level of the carrier of the adjacent interference wave in the intermediate frequency band from the electric field detector 106 and a predetermined level.
[0010]
The signal of the level difference is supplied to the controller 105. When the level difference from the adjacent interference detector 104 is large, the controller 105 can widen the bandwidth of the IF filter 101 and widely receive a desired wave. Conversely, if the level difference is small, the desired wave and the adjacent interference wave are close to each other, so that the bandwidth of the IF filter 101 is narrowed to block the adjacent interference wave (for example, see Patent Document 1).
[0011]
[Patent Document 1]
Japanese Patent No. 2,825,389
[Problems to be solved by the invention]
However, the above-described conventional FM tuner controls the bandwidth of the IF filter 101 in order to suppress the noise of the adjacent interference wave in the band of the FM detection output, the carrier level of the adjacent interference wave in the intermediate frequency band, and the like to predetermined values. ing. Therefore, when the band of the adjacent interference wave and the desired wave is close to each other or the modulation degree of the desired wave is large, the bandwidth of the IF filter 101 becomes excessively narrow, and the loss of the modulation degree of the desired wave is lost. And the FM detection characteristics (total harmonic distortion and the like) deteriorate.
[0013]
Further, since the output of the adjacent interference detector detects the noise level of the adjacent interference wave in the band of the FM detection output or the adjacent interference wave in the intermediate frequency band, a ripple occurs. Therefore, it is impossible to stably change the bandwidth of the IF filter 101 at the time of adjacent interference.
[0014]
Therefore, an object of the present invention is to provide an FM tuner that does not excessively narrow the bandwidth of an IF filter while receiving a desired wave.
[0015]
A further object of the present invention is to provide an FM tuner that enables a stable band change of the intermediate frequency filter at the time of adjacent interference.
[0016]
[Means for Solving the Problems]
According to one embodiment of the present invention, there is provided an intermediate processing filter to which an FM signal is input and which has a variable bandwidth, and amplifies the amplitude of the FM signal from the intermediate processing filter. An intermediate frequency limiter amplifier that converts the signal into a rectangular wave, an FM detector that performs FM detection on the FM signal from the intermediate frequency limiter amplifier, and an FM detection output output from the FM detector. An adjacent interference detector that generates a level difference between a noise level of an adjacent interference wave and a predetermined level; and a level of an FM signal supplied from between an output terminal of the intermediate frequency filter and an input terminal of the FM detector. An electric field detector for detecting an adjacent electric field, a weak electric field detector for generating a level difference between an electric field detection amount of the FM signal detected by the electric field detector and a predetermined level, And a controller to which the level difference generated by the weak electric field detector and the level difference generated by the weak electric field detector are supplied, wherein the controller generates the level difference generated by the adjacent interference detector and the level difference generated by the weak electric field detector. An FM tuner is provided, which generates a control signal for controlling the bandwidth of the intermediate frequency filter based on the level difference, and has a predetermined time constant for the control signal.
[0017]
According to another aspect of the present invention, an intermediate frequency filter to which an FM signal is input and whose bandwidth can be varied, the amplitude of the FM signal from the intermediate frequency filter is amplified, and the FM signal is converted into a rectangular wave An intermediate frequency limiter amplifier, an FM detector for performing FM detection on an FM signal from the intermediate frequency limiter amplifier, and an FM signal supplied from between an output terminal of the intermediate frequency filter and an input terminal of the FM detector. An electric field detector for detecting a level, a weak electric field detector for generating a level difference between an electric field detection amount of the FM signal detected by the electric field detector and a predetermined level, and an intermediate frequency band from the electric field detector. An adjacent interference detector that generates a level difference between the carrier level of the adjacent interference wave and a predetermined level; a level difference generated by the adjacent interference detector and a level difference generated by the weak electric field detector. A controller to which the difference is supplied, wherein the controller controls the bandwidth of the intermediate frequency filter based on the level difference generated by the adjacent interference detector and the level difference generated by the weak electric field detector. An FM tuner characterized in that a control signal is generated and a predetermined time constant is provided for the control signal.
[0018]
According to another aspect of the present invention, an intermediate frequency filter to which an FM signal is input and whose bandwidth can be varied, the amplitude of the FM signal from the intermediate frequency filter is amplified, and the FM signal is converted into a rectangular wave An intermediate frequency limiter amplifier, an FM detector for performing FM detection on an FM signal from the intermediate frequency limiter amplifier, and a noise of an adjacent interference wave in a band of the FM detection output based on an FM detection output output from the FM detector. An adjacent interference detector for generating a level difference from the level of the FM signal, a modulation degree detector for detecting a sound level of a desired wave from the FM detection output, an output terminal of the intermediate frequency filter, and an input terminal of the FM detector. An electric field detector for detecting the level of an FM signal supplied from between the detector and a level difference between an electric field detection amount of the FM signal detected by the electric field detector and a predetermined level A weak electric field detector, and a controller to which a level difference generated by the adjacent interference detector, an audio level generated by the modulation degree detector, and a level difference generated by the weak electric field detector are supplied. Generating a control signal for controlling the bandwidth of the intermediate frequency filter based on the level difference generated by the adjacent interference detector and the audio level and the level difference generated by the weak electric field detector; and An FM tuner is provided that has a predetermined time constant for a signal.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
[0020]
[First Embodiment] FIG. 1 is a configuration diagram of an FM tuner according to a first embodiment of the present invention.
[0021]
The IF filter 1 passes an FM signal having a bandwidth set around an intermediate frequency (for example, 450 kHz). The bandwidth can vary the −3 dB bandwidth from about 30 kHz to about 200 kHz.
[0022]
Here, the variable bandwidth means that two or more fixed bandwidths are set in advance and switched to the set bandwidth, and the bandwidth can be changed flexibly without fixing the bandwidth in advance. Things have both meanings.
[0023]
The FM signal that has passed through the IF filter 1 is supplied to an IF limiter amplifier 2. The IF limiter amplifier 2 amplifies the amplitude of the FM signal into a rectangular wave, and removes noise on the FM signal.
[0024]
The rectangular FM signal amplified by the IF limiter amplifier 2 is input to the FM detector 3. The FM detector 3 detects a rectangular wave formed by the IF limiter amplifier 2 and outputs an FM detection output (audio signal).
[0025]
The FM detection output is input to the adjacent interference detector 4. The adjacent interference detector 4 detects an interference wave adjacent to a desired signal of the FM signal.
[0026]
The adjacent interference detector 4 is configured as shown in FIG. 2, for example. The FM detection output from the FM detector 3 is input to a first band-pass filter 41 and a second band-pass filter. The first band-pass filter 41 is a filter having the center frequency f0 of the adjacent interference wave on the high frequency side. The second bandpass filter 42 is a filter having the center frequency f0 of the adjacent interference wave on the low frequency side.
[0027]
The signals that have passed through the first and second band-pass filters 41 and 42 are input to a combining circuit 43, and these signals are combined. In the synthesis circuit 43, for example, addition or OR operation is performed. The detection circuit 44 generates a difference between the output level from the synthesis circuit 43 and a predetermined level. This level difference is supplied to the controller 5.
[0028]
Information on the detected interference wave is input to the controller 5. The controller 5 is a circuit that controls the IF filter 1 so that the FM tuner excludes an interference wave other than a desired wave, particularly an adjacent interference wave.
[0029]
The IF limiter amplifier 2 is also connected to the electric field detector 6. The IF limiter amplifier 2 is configured by a circuit in which several stages of buffer circuits are connected in series. The electric field detector 6 uses the outputs of the plurality of buffer circuits of the IF limiter amplifier 2 as input signals, and detects the signal strength of the FM signal.
[0030]
The output signal of the electric field detector 6 is input to the weak electric field detector 7. The weak electric field detector 7 is a detector that monitors the signal strength of the FM signal and detects a predetermined electric field or less (a weak electric field). The output signal of the weak electric field detector 7 is also input to the controller 5.
[0031]
The controller 5 controls to increase the bandwidth of the IF filter 1 when the level difference input from the adjacent interference detector 4 is large, that is, when the desired wave and the adjacent interference wave are not close to each other. On the other hand, when the level difference input from the adjacent interference detector 4 is small, that is, when the desired wave and the adjacent interference wave are close to each other, control is performed so as to narrow the bandwidth of the IF filter 1.
[0032]
Further, when the signal intensity of the FM signal input from the weak electric field detector 7 is small, that is, when the desired wave is a weak electric field, the controller 5 controls to increase the bandwidth of the IF filter 1.
[0033]
Normally, in the case of a weak electric field, the setting of the detection sensitivity of the adjacent interference detector 4 must be reduced in advance in order to prevent malfunction of the band control of the IF filter 1 due to the noise of the FM detection output or the electric field detection output. Therefore, the adjacent interference detector 4 cannot detect the original adjacent interference wave, and the bandwidth of the IF filter 1 cannot be increased even if the adjacent interference wave is relatively far from the desired wave. The bandwidth of the IF filter 1 whose bandwidth can be broadened is also narrowed.
[0034]
However, when the weak electric field is detected by the weak electric field detector 7, the bandwidth of the IF filter 1 is widened, so that the detection sensitivity of the adjacent interference detector 4 is improved, the adjacent interference wave is effectively detected, and the IF filter 1 is adjusted. be able to.
[0035]
Further, as shown in FIG. 3, even if the adjacent interference detector 4 of the present embodiment is inserted between the electric field detector 6 and the controller 5, the adjacent interference wave can be detected, and the effect of the present invention can be obtained.
[0036]
[Second Embodiment] FIG. 4 is a block diagram of an FM tuner according to a second embodiment of the present invention.
[0037]
The IF filter 1, the IF limiter amplifier 2, the FM detector 3, the adjacent interference detector 4, the controller 5, the electric field detector 6, and the weak electric field detector 7 have the configuration of the FM tuner of FIG. 1 described in the first embodiment. Therefore, the description is omitted.
[0038]
The FM tuner shown in FIG. 4 has a configuration in which a modulation degree detector 8 is inserted between the FM detector 3 and the controller 5 of the FM tuner shown in FIG.
[0039]
The modulation degree detector 8 detects the sound level of a desired wave from the FM detection output of the FM detector 3. The larger the degree of modulation of the desired wave (frequency modulation from the center frequency f0 of the desired wave), the higher the sound level signal. This audio level is supplied to the controller 5. Here, the sound level output from the modulation degree detector 8 basically does not include noise of an adjacent interference wave in a band of a detection output, a carrier level in an intermediate frequency band, and the like.
[0040]
The signals detected by the adjacent interference detector 4, the weak electric field detector 7, and the modulation degree detector 8 are input to the controller 5.
[0041]
Control is performed such that the larger the level difference input from the adjacent interference detector 4 is, the wider the bandwidth of the IF filter 1 is, and the smaller the level difference is, the narrower the bandwidth of the IF filter 1 is.
[0042]
Further, when the signal strength of the FM signal input from the weak electric field detector 7 is low, control is performed so as to widen the bandwidth of the IF filter 1.
[0043]
Further, when the degree of modulation of the desired wave input from the degree-of-modulation detector 8 is large, that is, when the sound level is large, control is performed to increase the bandwidth of the IF filter 1. Loss of the modulation degree of the desired wave can be suppressed as much as possible, and the FM detection characteristics (total harmonic distortion and the like) can be improved.
[0044]
As described above, the controller 5 can be controlled based on the information obtained from the received FM signals by the respective detectors, and the optimum bandwidth of the IF filter 1 can be determined.
[0045]
Note that the adjacent interference detector 4 may be inserted between the electric field detector 6 and the controller 5 as in the first embodiment.
[0046]
[Third Embodiment] FIG. 5 shows a configuration diagram of an FM tuner according to a third embodiment of the present invention.
[0047]
The IF filter 1, the IF limiter amplifier 2, the FM detector 3, the adjacent interference detector 4, the controller 5, the electric field detector 6, and the weak electric field detector 7 have the configuration of the FM tuner of FIG. 1 described in the first embodiment. Therefore, the description is omitted.
[0048]
The FM tuner shown in FIG. 5 has a configuration in which a mute circuit 9 is inserted between the FM detector 3 and the adjacent interference detector 4. This mute circuit 9 is controlled by the output of the electric field detector 6. When the electric field detector 6 determines that the electric field is weak, the FM detection output is muted by the mute circuit 9.
[0049]
The FM detection output is controlled by the mute circuit 9 so as to alleviate the deterioration of the listening quality due to the increase in the noise of the FM detection output at the time of a weak electric field. But you can avoid it. Therefore, even in the case of a weak electric field, it is not necessary to lower the detection sensitivity of the adjacent interference detector 4 in advance, and the detection sensitivity of the adjacent interference detector 4 is improved, and the IF filter 1 is adjusted by effectively detecting the adjacent interference wave. can do.
[0050]
The signals detected by the adjacent interference detector 4 and the weak electric field detector 7 are input to the controller 5.
[0051]
Control is performed such that the larger the level difference input from the adjacent interference detector 4 is, the larger the bandwidth of the IF filter 1 is, and the smaller the level difference is, the narrower the bandwidth of the IF filter 1 is.
[0052]
Further, when the signal strength of the FM signal input from the weak electric field detector 7 is low, control is performed so as to widen the bandwidth of the IF filter 1.
[0053]
As described above, the controller 5 can be controlled based on the information obtained from the received FM signals by the respective detectors, and the optimum bandwidth of the IF filter 1 can be determined.
[0054]
Note that the adjacent interference detector 4 may be inserted between the electric field detector 6 and the controller 5 as in the first embodiment.
[0055]
[Fourth Embodiment] FIG. 6 shows a configuration diagram of an FM tuner according to a fourth embodiment of the present invention.
[0056]
The IF filter 1, the IF limiter amplifier 2, the FM detector 3, the adjacent interference detector 4, the controller 5, the electric field detector 6, the weak electric field detector 7, and the mute circuit 9 shown in FIG. 5 described in the third embodiment Since the configuration is the same as that of the FM tuner, the description is omitted.
[0057]
The FM tuner shown in FIG. 6 has a configuration in which a modulation degree detector 8 is inserted between the FM detector 3 and the controller 5 of the FM tuner shown in FIG. The modulation degree detector 8 is the same as the modulation degree detector 8 described in the second embodiment, and a description thereof will be omitted.
[0058]
The signals detected by the adjacent interference detector 4, the weak electric field detector 7, and the modulation degree detector 8 are input to the controller 5.
[0059]
Control is performed such that the larger the level difference input from the adjacent interference detector 4 is, the wider the bandwidth of the IF filter 1 is, and the smaller the level difference is, the narrower the bandwidth of the IF filter 1 is.
[0060]
Further, when the signal strength of the FM signal input from the weak electric field detector 7 is low, control is performed so as to widen the bandwidth of the IF filter 1.
[0061]
Further, when the degree of modulation of the desired wave input from the degree-of-modulation detector 8 is large, that is, when the sound level is large, control is performed to increase the bandwidth of the IF filter 1.
[0062]
As described above, the controller 5 can be controlled from the information obtained from the received FM signals by the respective detectors, and the optimum bandwidth of the IF filter 1 can be determined.
[0063]
Note that the adjacent interference detector 4 may be inserted between the electric field detector 6 and the controller 5 as in the first embodiment.
[0064]
The above-described FM tuner of the present invention has a predetermined time constant for controlling the IF filter 1 in order to prevent circuit oscillation. For example, the controller 5 may be provided with an integrator.
[0065]
【The invention's effect】
As described in detail above, the present invention provides an FM tuner that enables a stable change of the band of the intermediate frequency filter during adjacent interference without excessively narrowing the bandwidth of the IF filter during reception of a desired wave. Can be provided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an FM tuner circuit according to a first embodiment of the present invention.
FIG. 2 is a configuration diagram illustrating an example of an adjacent interference detector of FIG.
FIG. 3 is a configuration diagram illustrating a modification of the FM tuner circuit according to the first embodiment of the present invention.
FIG. 4 is a configuration diagram of an FM tuner circuit according to a second embodiment of the present invention.
FIG. 5 is a configuration diagram of an FM tuner circuit according to a third embodiment of the present invention.
FIG. 6 is a configuration diagram of an FM tuner circuit according to a fourth embodiment of the present invention.
FIG. 7 is a configuration diagram of a conventional FM tuner circuit.
FIG. 8 is a configuration diagram of a conventional FM tuner circuit.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 IF filter 2 IF limiter amplifier 3 FM detector 4 Adjacent interference detector 41 First bandpass filter 42 Second bandpass filter 43 ..Synthesis circuit 44 Detection circuit 5 Controller 6 Electric field detector 7 Weak electric field detector 8 Modulation degree detector 9 Mute circuit

Claims

An intermediate processing filter to which an FM signal is input and which can change a bandwidth;
An intermediate frequency limiter amplifier that amplifies the amplitude of the FM signal from the intermediate processing filter and converts the FM signal into a rectangular wave;
An FM detector for FM-detecting the FM signal from the intermediate frequency limiter amplifier,
An adjacent interference detector that generates a level difference between a noise level of an adjacent interference wave and a predetermined level in a band of the FM detection output from the FM detection output output from the FM detector;
An electric field detector for detecting a level of an FM signal supplied from an output terminal of the intermediate frequency filter and an input terminal of the FM detector;
A weak electric field detector for generating a level difference between an electric field detection amount of the FM signal detected by the electric field detector and a predetermined level;
A controller to which a level difference generated by the adjacent interference detector and a level difference generated by the weak electric field detector are supplied,
The controller generates a control signal for controlling a bandwidth of the intermediate frequency filter based on a level difference generated by the adjacent interference detector and a level difference generated by the weak electric field detector, and the control signal An FM tuner characterized by having a predetermined time constant.

A variable bandwidth intermediate frequency filter to which an FM signal is input;
An intermediate frequency limiter amplifier that amplifies the amplitude of the FM signal from the intermediate frequency filter and converts the FM signal into a rectangular wave;
An FM detector for FM-detecting the FM signal from the intermediate frequency limiter amplifier,
An electric field detector for detecting a level of an FM signal supplied from an output terminal of the intermediate frequency filter and an input terminal of the FM detector;
A weak electric field detector for generating a level difference between an electric field detection amount of the FM signal detected by the electric field detector and a predetermined level;
An adjacent interference detector that generates a level difference between a carrier level and a predetermined level of an adjacent interference wave in an intermediate frequency band from the electric field detector,
A controller to which a level difference generated by the adjacent interference detector and a level difference generated by the weak electric field detector are supplied,
The controller generates a control signal for controlling a bandwidth of the intermediate frequency filter based on a level difference generated by the adjacent interference detector and a level difference generated by the weak electric field detector, and the control signal An FM tuner characterized by having a predetermined time constant.

A variable bandwidth intermediate frequency filter to which an FM signal is input;
An intermediate frequency limiter amplifier that amplifies the amplitude of the FM signal from the intermediate frequency filter and converts the FM signal into a rectangular wave;
An FM detector for FM-detecting the FM signal from the intermediate frequency limiter amplifier,
An adjacent interference detector that generates a level difference from a noise level of an adjacent interference wave in the band of the FM detection output from the FM detection output output from the FM detector;
A modulation degree detector for detecting a sound level of a desired wave from the FM detection output;
An electric field detector for detecting a level of an FM signal supplied from an output terminal of the intermediate frequency filter and an input terminal of the FM detector;
A weak electric field detector for generating a level difference between an electric field detection amount of the FM signal detected by the electric field detector and a predetermined level;
A controller to which a level difference generated by the adjacent interference detector and a sound level generated by the modulation degree detector and a level difference generated by the weak electric field detector are supplied.
A control signal for controlling a bandwidth of the intermediate frequency filter is generated based on a level difference generated by the adjacent interference detector and a level difference generated by the audio level and the weak electric field detector, and the control signal An FM tuner characterized by having a predetermined time constant.

A mute circuit that mutes the FM detection output according to the level of the FM signal detected by the electric field detector;
The output signal of the mute circuit is input to the adjacent interference detector, and the bandwidth of the intermediate frequency filter is determined by the difference between the noise level of the adjacent interference wave in the band of the FM detection output via the mute circuit and a predetermined level. The FM tuner according to any one of claims 1 to 3, wherein the FM tuner is controlled.

The control signal for controlling the bandwidth of the intermediate frequency filter increases the bandwidth of the intermediate frequency filter when the level difference generated by the adjacent interference detector is large, and increases the bandwidth of the intermediate frequency filter when the level difference is small. The bandwidth of the intermediate frequency filter is increased when the FM signal is detected by the weak electric field detector as being in a weak electric field. The FM tuner according to any one of claims 1 to 4.

The control signal for controlling the bandwidth of the intermediate frequency filter increases the bandwidth of the intermediate frequency filter when the modulation level detector has a high sound level of the FM signal. FM tuner.