JP3766472B2 - Tuning circuit - Google Patents

Description

となる。
【００３９】
この（５）式によれば、ω＝０（直流の領域）のときにＡ＝−１／（２ｎ＋１）となって、最大減衰量を与えることがわかる。また、ω＝∞のときにもＡ＝−１／（２ｎ＋１）となって、最大減衰量を与えることがわかる。さらに、ω＝１／Ｔの同調点（一般には各移相回路の時定数が異なるので、ω＝１／√（Ｔ₁ ・Ｔ₂ ）の同調点）においてはＡ＝１であって図１に示した抵抗７０と７４の抵抗比ｎに無関係であって、図９に示すように、同調帯域幅（すなわちＱ）と最大減衰量が任意に設定可能なバンドパスフィルタとして動作することがわかる。
【００４０】
また、上述した同調回路１は、前段の移相回路１０Ｌに含まれるインダクタ１７をアンテナコイルによって形成しているため、放送波等の各種の受信信号を直接同調回路１に取り込むことができ、従来不可欠であったバリコンが不要となる。このため、アンテナコイルを除く同調回路１全体を半導体基板上に形成することができ、集積化にも適する。
【００４１】
また、同調回路１の後段の移相回路３０Ｃに含まれる可変抵抗３６の抵抗値を可変することにより、閉ループを一巡したときの位相シフト量の合計が３６０°となる周波数を変えることができる。したがって、同調回路１の中心周波数（同調周波数）を任意に変えることができ、必ずしも従来のようにスーパーヘテロダイン方式を用いなくとも受信機を構成することができる。このため、スーパーヘテロダイン方式の受信機では不可欠であった中間周波トランスや局部発振トランス等が不要となり、同調機構全体、さらには受信機のほとんどを半導体基板上に一体形成することも可能となる。
【００４２】
また、前段の移相回路１０Ｌの入力側に接続された可変抵抗７４の抵抗値を変えることにより同調帯域幅、すなわちバンドパスフィルタのＱを可変することができる。これにより、同調回路１を用いて構成した受信機において、混信が生じる場合には可変抵抗７４の抵抗値を調整することにより同調帯域幅を狭くして混信を防ぎ、反対に混信が少ない場合においては可変抵抗７４の抵抗値を調整することにより同調帯域幅を広げて受信信号を忠実に再現することが可能となり、混信状態に応じて最適な受信機を設計できる。
【００４３】
なお、上述した同調回路はＦＥＴを用いて各移相回路を構成したが、バイポーラ型のトランジスタを用いて各移相回路を構成してもよい。バイポーラ型のトランジスタを用いると、ＦＥＴを用いた場合に比べて各移相回路を通過する際の信号振幅の減衰が少なくなるため、後段の非反転回路や位相反転回路の増幅度を低くすることができる。ただし、後段の移相回路内にバイポーラトランジスタを設けると、バイポーラトランジスタは入力インピーダンスが低いことから、前段の移相回路の位相シフト量が変化するおそれがある。このため、信号振幅の減衰を少なくするために前段の移相回路内にバイポーラトランジスタを設け、かつ高入力インピーダンスとするために後段の移相回路内にＦＥＴを設けるのがより望ましい。
【００４４】
〔第２の実施形態〕
図１０は、第２の実施形態の同調回路の構成を示す回路図であり、図１に示した同調回路１の前段および後段の移相回路１０Ｌ、３０Ｃをそれぞれ移相回路３０Ｌ、１０Ｃに置き換えた構成を有している。
【００４５】
図１０に示す前段の移相回路３０Ｌは、図１に示した移相回路３０Ｃ内のキャパシタ３４と可変抵抗３６からなるＣＲ回路を、抵抗３５とインダクタ３７からなるＬＲ回路に置き換えたものであり、このインダクタ３７はアンテナコイルを用いて形成されており、移相回路３０Ｌの入出力電圧の関係は移相回路３０Ｃの入出力電圧間の関係と同じである。
【００４６】
同様に、図１０に示した後段の移相回路１０Ｃは、図１に示した移相回路１０Ｌ内のインダクタ１７と抵抗１６からなるＬＲ回路を、可変抵抗１５とキャパシタ１４からなるＣＲ回路に置き換えたものである。この移相回路１０Ｃの入出力電圧の関係は移相回路１０Ｌの入出力電圧との関係と同じである。
【００４７】
このように、同調回路１Ａ内の移相回路３０Ｌ、１０Ｃは、図１に示した同調回路１内の２つの移相回路１０Ｌ、３０Ｃと等価であり、前段の移相回路３０Ｌ内にアンテナコイルにより構成したインダクタ３７を含むことも同じであるから、図１に示した同調回路１と同様の効果が得られる。
【００４８】
〔第３の実施形態〕
上述した第１の実施形態の同調回路１、１Ａは、各同調回路を構成する２つの移相回路による位相シフト量の合計が３６０°となる周波数で所定の同調動作を行っていたが、２つの移相回路による位相シフト量の合計が１８０°となる周波数で所定の同調増幅を行うようにしてもよい。
【００４９】
図１１は、第３の実施形態の同調回路１Ｂの詳細な構成を示す回路図である。同図に示す同調回路１Ｂは、所定の周波数において合計で１８０°の位相シフトを行う２つの移相回路１０Ｌおよび１０Ｃと、後段の移相回路１０Ｃの出力信号の位相をさらに反転する位相反転回路８０と、帰還抵抗７０と、可変抵抗７４とを含んで構成されている。
【００５０】
前段の移相回路１０Ｌは、その詳細構成および入出力信号の位相関係は図２および図３を用いて説明した通りであり、例えば抵抗１６とインダクタ１７からなるＬＲ回路の時定数をＴ₁ とすると、ω＝１／Ｔ₁ 近傍の周波数において位相シフト量φ1 がほぼ９０°となる。
【００５１】
また、後段の移相回路１０Ｃの入出力電圧の関係は、第１図に示した前段の移相回路１０Ｌの入出力電圧の関係と同じであり、例えばキャパシタ１４と可変抵抗１５からなるＣＲ回路の時定数をＴ₁ ′とすると、ω＝１／Ｔ₁ ′近傍の周波数において位相シフト量φ1 ′はほぼ９０°となる。
【００５２】
このように、２つの移相回路１０Ｌおよび１０Ｃの全体による位相シフト量の合計が所定の周波数において、φ1 ＋φ1 ′＝１８０°となる。
【００５３】
また、位相反転回路８０は、ドレインと正電源との間に抵抗８４が、ソースとアースとの間に抵抗８６がそれぞれ接続されたＦＥＴ８２と、ＦＥＴ８２のゲートに所定のバイアス電圧を印加する抵抗８８とを含んで構成されている。ＦＥＴ８２のゲートに交流信号が入力されると、トランジスタ８２のドレインからは位相を反転した逆相の信号が出力される。また、この位相反転回路８０は、２つの抵抗８４、８６の抵抗比によって定まる所定の増幅度を有する。
【００５４】
このように、所定の周波数において、２つの移相回路１０Ｌおよび１０Ｃによって位相が１８０°シフトされ、さらに後段に接続された位相反転回路８０によって位相が反転され、これら３つの回路の全体による位相シフト量の合計が３６０°となる。
【００５５】
また、位相反転回路８０の出力は、出力端子９２から同調回路１Ｂの出力として取り出されるとともに、その出力を分圧回路１６０により分圧した電圧が帰還抵抗７０を介して前段の移相回路１０Ｌの入力側に帰還されている。
【００５６】
このように、一方の移相回路１０Ｌにアンテナコイルで形成したインダクタ１７を含めるとともに、位相反転回路８０の出力を帰還抵抗７０を介して前段の移相回路１０Ｌの入力側に帰還させ、この帰還ループのループゲインを１以下に設定することにより、所定の同調動作を行わせることができる。したがって、図１に示した同調回路１等と同様に、任意に同調周波数を変えることができ、バリコンが不要であって集積化に適するという特長を有している。
【００５７】
〔第４の実施形態〕
図１１に示した同調回路は、移相回路１０Ｌと１０Ｃを縦続接続する例を示したが、図１２に示すように移相回路３０Ｌと３０Ｃを縦続接続する場合も同調動作を行わせることができる。
【００５８】
２つの移相回路３０Ｌおよび３０Ｃの全体による位相シフト量の合計が所定の周波数において、φ2 ′＋φ2 ＝１８０°となり、この所定の周波数において、２つの移相回路３０Ｌおよび３０Ｃによって位相が１８０°シフトされ、さらに後段に接続された位相反転回路８０によって位相が反転され、これら３つの回路の全体による位相シフト量の合計が３６０°となる。
【００５９】
〔第５の実施形態〕
上述した各種の同調回路では、アンテナコイルで形成したインダクタを移相回路内に設ける例を説明したが、ＡＭ受信機等のバーアンテナの１次コイルおよび２次コイルを利用して同調回路を構成することもできる。
【００６０】
図１３は同調回路の第５の実施形態の詳細構成を示す回路図である。同図に示す同調回路１Ｄは、移相回路１１０Ｌと、移相回路３０Ｃと、非反転回路８０とを縦続接続して構成され、移相回路１１０Ｌは抵抗１６およびインダクタ１１７ＡからなるＬＲ回路を含んでいる。インダクタ１１７Ａは、ＡＭ受信機等のバーアンテナの１次コイルを用いて構成され、この１次コイルには２次コイル１１７Ｂが磁気結合されており、この２次コイル１１７Ｂの両端から同調回路の出力、すなわち同調信号が取り出される。また、図１３に示す同調回路１内の後段の移相回路３０Ｃの出力は分圧回路を介することなく前段の移相回路１１０Ｌの入力側に帰還されている。その他の構成は、図１に示した同調回路と共通する。
【００６１】
図１４は、図１３に示す同調回路を含むＡＭ受信機のブロック構成図である。同図に示すＡＭ受信機は、図１３に示した同調回路１Ｄ、ＡＭ検波回路２、低周波増幅回路３およびスピーカ４を含んで構成され、ＡＭ検波回路２には同調回路１内の２次コイルから出力される同調信号が入力される。
【００６２】
図１４に示すＡＭ受信機において、同調回路に含まれるバーアンテナ１７によりＡＭ波が受信されるとバーアンテナ１１７の１次コイルからなるインダクタ１１７Ａの両端にはＡＭ波に含まれる各種周波数の交流電圧が発生する。この各種周波数の交流信号の中で、２つの移相回路１１０Ｌ、３０Ｃを合わせた位相シフト量の合計が３６０°以外の成分は同調回路１Ｄの閉ループを介して帰還されることにより減衰し、その結果位相シフト量の合計が３６０°となる周波数成分のみが選択されて、２次コイル１１７Ｂから同調信号として出力される。この同調信号はＡＭ検波回路２でＡＭ検波されて音声信号に変換された後、低周波増幅回路３で増幅されてスピーカ４から出力される。
【００６３】
このように、前段の移相回路１１０Ｌ内のインダクタ１１７Ａをバーアンテナ１１７の１次コイルにより構成したため、バーアンテナ１１７で受信した放送波等の各種の受信信号を直接同調回路１Ｄに取り込むことができ、従来不可欠であったバリコンが不要となる。このため、バーアンテナ１１７を除く同調回路１Ｄ全体を半導体基板上に形成することができ、小型化およびコストの低減が図れる。
【００６４】
また、１次コイルと磁気結合された２次コイル１１７Ｂから同調信号を取り出すため、直流成分をカットすることができ、次段の回路との接続が容易になる。なお、実際に図１３に示す同調回路１を組み立てて出力波形を測定したところ、閉ループの一部から同調信号を直接取り出す場合に比べてノイズを低減することができた。
【００６５】
また、例えば従来のＡＭ受信機のようにＬＣ共振回路によって同調を行う場合には、使用するバリコンの静電容量や可変範囲の制約から、バーアンテナ１１７のインダクタンスを十分に大きくする必要があった。これに対し、本実施形態の同調回路１では、インダクタンスを抵抗と組み合わせているため、インダクタのインダクタンスをある程度自由に設定することができる。したがって、バーアンテナのインダクタンスを従来より小さくすることができ、受信機全体を小型化できる。
【００６６】
なお、図１４では、図１に示した同調回路をＡＭ受信機に適用した例を説明したが、ＦＭ受信機に適用することも可能である。その場合には、図１４に示すＡＭ検波回路をＦＭ検波回路に置き換えればよい。
【００６７】
〔第６の実施形態〕
図１３では、図１に示した前段の移相回路内のインダクタをバーアンテナの１次コイルに置き換えた例を説明したが、同様に、図１０、１１、１２に示す同調回路１Ａ、１Ｂ、１Ｃのそれぞれについても、前段の移相回路内のインダクタをバーアンテナの１次コイルに置き換え、このバーアンテナの２次コイルから同調出力を取り出すようにしてもよい。
【００６８】
図１５、１６、１７のそれぞれは、図１０、１１、１２に示した前段の移相回路内のインダクタをバーアンテナの１次コイルに置き換えるとともに、分圧回路１６０を取り除いた例を示す回路図である。
【００６９】
図１５、１６、１７のいずれの場合も、１次コイルと磁気結合された２次コイルから同調信号を取り出すため、直流分をカットすることができ、次段の回路との接続が容易になる。
【００７０】
〔その他の実施形態〕
本発明は上記実施形態に限定されるものではなく、本発明の要旨の範囲内で種々の変形実施が可能である。
【００７１】
例えば、上述した各種の同調回路は、位相シフトに着目すると２つの移相回路と非反転回路、あるいは２つの移相回路と位相反転回路によって構成されており、接続された３つの回路の全体によって所定の周波数において合計の位相シフト量を３６０°にすることにより所定の同調動作を行うようになっている。したがって、位相シフト量だけに着目すると、２つの移相回路のどちらを前段に用いるか、あるいは３つの回路をどのような順番で接続するかはある程度の自由度があり、必要に応じて接続順番を決めることができる。
【００７２】
また、上述した各種の同調回路においては、アンテナコイルやバーアンテナ１１７の１次コイルにより構成されたインダクタを前段の移相回路内に設けているが、前段と後段の移相回路の配置を入れ換えて、後段の移相回路内にインダクタを設けてもよい。
【００７３】
また、上述した各種の同調回路においては、ＬＲ回路を内部に含む移相回路とＣＲ回路を内部に含む移相回路を縦続接続する例を説明したが、ＬＲ回路を内部に含む２つの移相回路を縦続接続してもよい。
【００７４】
また、上述した各種の同調回路においては、一方の移相回路のみに可変抵抗を設けているが、両方の移相回路内に可変抵抗を設けてもよい。例えば、図１に示した抵抗１６を可変抵抗に置き換えてもよい。両方の移相回路内に可変抵抗を設けると、２つの移相回路による位相シフト量の合計を大きくできるため、同調回路全体の同調周波数の可変範囲を広げることができる。
【００７５】
また、第４の実施形態までに示した各種の同調回路においては、後段の移相回路の出力側に分圧回路を接続しているが、この分圧回路を省略し、後段の移相回路の出力を直接前段の移相回路の入力側に帰還させてもよい。
【００７６】
なお、上述した各種の同調回路内の可変抵抗（例えば図１の可変抵抗３６）は、例えばＦＥＴによって構成できる。この場合、１個のＦＥＴによって可変抵抗を構成してもよいが、ｐチャネルのＦＥＴとｎチャネルのＦＥＴとを並列接続して１つの可変抵抗を構成してもよい。このように、２つのＦＥＴを組み合わせて可変抵抗を構成することにより、ＦＥＴの非線形領域の改善を行うことができるため、同調出力の歪みを少なくすることができる。
【００７７】
【発明の効果】
上述したように本発明の同調回路は、所定の同調周波数を有するバンドパスフィルタとして動作し、しかも一方の移相回路に含まれるインダクタをアンテナコイルによって形成しているため、放送波等の各種の受信信号を直接同調回路に取り込むことができ、従来不可欠であったバリコンが不要となる。このため、インダクタを除く同調回路全体を半導体基板上に形成することができ、集積化に適する。
【００７８】
また、少なくとも一方の移相回路に含まれる可変抵抗の抵抗値を可変することにより、同調回路の閉ループを一巡したときに位相量の合計が３６０°となる周波数を変えることができるため、同調周波数を任意に変えることができ、必ずしも従来のようにスーパーヘテロダイン方式を用いなくとも受信機を構成することが可能となる。このため、スーパーヘテロダイン方式の受信機では不可欠であった中間周波トランスや局部発振トランス等が不要となり、同調機構全体、さらには受信機のほとんどを半導体基板上に一体形成することも可能となる。
【００７９】
また、前段の移相回路の入力側に接続された抵抗あるいは帰還抵抗の少なくとも一方の抵抗値を変えることにより同調帯域幅、すなわちバンドパスフィルタのＱを可変することができるため、例えば同調回路を用いて構成した受信機において、混信が生じる場合には同調帯域幅を狭くして混信を防ぎ、反対に混信が少ない場合においては同調帯域幅を広げて受信信号を忠実に再現するといったことが可能であり、混信状態に応じて最適な受信機の設計が可能となる。
【００８０】
また、バーアンテナ等の２次コイルから同調信号を出力するため、同調信号に含まれる直流成分を除去することができ、次段の回路との接続が容易になる。
【図面の簡単な説明】
【図１】第１の実施形態の同調回路の構成を示す回路図である。
【図２】図１に示す前段の移相回路の構成を示す回路図である。
【図３】図２に示した移相回路の入出力電圧とインダクタ等に現れる電圧の関係を示すベクトル図である。
【図４】図１に示す後段の移相回路の構成を示す回路図である。
【図５】図４に示した移相回路の入出力電圧とキャパシタ等に現れる電圧の関係を示すベクトル図である。
【図６】図１に示した同調回路の一部に対応した等価回路を示す図である。
【図７】同調回路内の２つの移相回路および分圧回路の全体を所定の伝達関数を有する回路に置き換えた図である。
【図８】図７に示す回路をミラーの定理によって変換した図である。
【図９】図１に示す同調回路の特性図である。
【図１０】第２の実施形態の同調回路の構成を示す回路図である。
【図１１】第３の実施形態の同調回路の構成を示す回路図である。
【図１２】第４の実施形態の同調回路の構成を示す回路図である。
【図１３】第５の実施形態の同調回路の構成を示す回路図である。
【図１４】図１３に示す同調回路を含むＡＭ受信機のブロック構成図である。
【図１５】図１０に示した前段の移相回路内のインダクタをバーアンテナの１次コイルに置き換えた例を示す回路図である。
【図１６】図１１に示した前段の移相回路内のインダクタをバーアンテナの１次コイルに置き換えた例を示す回路図である。
【図１７】図１２に示した前段の移相回路内のインダクタをバーアンテナの１次コイルに置き換えた例を示す回路図である。
【符号の説明】
１ 同調回路
１０Ｌ、３０Ｃ 移相回路
１２、３２ ＦＥＴ
１３、３４ キャパシタ
１６、１８、２０、３８、４０ 抵抗
１７ インダクタ
３６、７４ 可変抵抗
７０ 帰還抵抗
１６０ 分圧回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tuning circuit used for a radio receiver or the like.
[0002]
[Prior art]
Various receivers such as AM radios receive signals of various frequencies. To select and receive a desired signal from these signals, the input circuit has the characteristics of a bandpass filter. You can do it. In addition, in order to select one of a plurality of broadcast waves distributed over a wide range such as AM radio, the center frequency of the bandpass filter may be arbitrarily changed. In the past, there was no bandpass filter with a super-heterodyne method. In this superheterodyne system, only the desired signal is extracted by converting the frequency of the broadcasting station to the center frequency of the bandpass filter without changing the center frequency of the bandpass filter.
[0003]
[Problems to be solved by the invention]
By the way, in the conventional receiver described above, a tuning circuit is formed by an LC resonance circuit using a bar antenna and a variable capacitor, and the variable capacitor is an indispensable component. In addition, a receiver using the superheterodyne system has a tuning mechanism that links the tuning frequency by the input circuit and the oscillation frequency of the local oscillation circuit in order to improve selectivity, and this linkage is a double variable condenser. Had gone by. Since the above-described variable capacitors and double variable capacitors are made to have a predetermined capacitance according to the reception frequency and are determined in size, it is difficult to reduce the size and integration of the entire tuning mechanism.
[0004]
In addition, local oscillator transformers and intermediate frequency transformers are used in local oscillator circuits and intermediate frequency amplifier circuits of conventional receivers using the superheterodyne method (recently, intermediate frequency amplification is performed using a ceramic filter). These transformers are external components, and it is difficult to integrate the entire tuning mechanism from this point.
[0005]
The present invention has been created in view of the above points, and an object of the present invention is to provide a tuning circuit that does not require a variable capacitor and is suitable for integration.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problem, the tuning circuit of the present invention cascades two phase shift circuits and a non-inverting circuit in a predetermined order, and feeds back the output of the final stage circuit to the input side of the first stage circuit. Let The sum of the phase shift amounts of the two phase shift circuits as a whole is 360 ° at a predetermined frequency, and the tuning operation is performed at this frequency. In addition, since the inductor included in one of the phase shift circuits is formed by an antenna coil, various received signals such as broadcast waves can be directly taken into the tuning circuit, eliminating the need for a variable capacitor that has been indispensable in the past.
[0007]
The tuning circuit according to claim 2 and 5 includes a voltage dividing circuit inserted in a part of a closed loop formed by including two phase shift circuits, and an AC signal input to the voltage dividing circuit is extracted as a tuning output. The output amplitude can be increased.
[0008]
Since the tuning circuit according to claims 3 and 6 includes a phase shift circuit including an LR circuit including an inductor formed of a primary coil of the antenna and a first resistor, a tuning signal is extracted from the secondary coil. By doing so, the DC component can be cut efficiently, and the connection with the circuit of the next stage becomes easy.
[0009]
The tuning circuit of claim 4 cascade-connects two phase shift circuits and a phase inversion circuit in a predetermined order, and feeds back the output of the final stage circuit to the input side of the first stage circuit. The total amount of phase shift by the two phase shift circuits as a whole is 180 ° at a predetermined frequency, and the tuning operation is performed at this frequency.
[0010]
Each phase shift circuit in the tuning circuit according to claim 7 outputs a signal whose phase is shifted by a predetermined amount together with each phase shift circuit in order to synthesize the AC signal converted by the conversion means via the LR circuit or the CR circuit. can do.
[0011]
In the tuning circuit according to the eighth aspect, since the conversion means is configured using transistors, the circuit configuration can be simplified.
[0012]
Since the tuning circuit according to claims 9 and 10 varies the time constant of at least one of the CR circuit or the LR circuit in the two phase shift circuits, the tuning frequency can be arbitrarily changed.
[0013]
The tuning circuit according to claim 11 includes a fourth resistor inserted into a part of a closed loop formed including two phase shift circuits, and a fifth resistor for branching a part of the AC signal flowing through the closed loop. Therefore, the tuning bandwidth can be changed by varying the resistance ratio of the fourth and fifth resistors.
[0014]
The tuning circuit of the twelfth aspect sets a loop gain of a closed loop including two phase shift circuits to 1 or less, so that it does not oscillate and a stable tuning operation is performed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment to which a tuning circuit of the present invention is applied will be described in detail with reference to the drawings.
[0016]
[First Embodiment]
FIG. 1 is a circuit diagram showing a configuration of a tuning circuit according to the first embodiment. The tuning circuit 1 shown in the figure has a predetermined frequency without changing the phase of the output signals of the two phase shift circuits 10L and 30C that shift the phase of the AC signal having a predetermined frequency by a total of 360 ° and the phase shift circuit 30C in the subsequent stage. A non-inverting circuit 50 that amplifies and outputs with the degree of amplification, a voltage dividing circuit 160 comprising resistors 162 and 164 provided at the subsequent stage of the non-inverting circuit 50, and an output of the voltage dividing circuit 160 of the phase shift circuit 10L of the preceding stage The feedback resistor 70 is fed back to the input side, and the variable resistor 74 is provided to branch a part of the signal fed back through the feedback resistor 70.
[0017]
Both the capacitor 72 connected in series with the feedback resistor 70 and the capacitor 73 connected in series with the variable resistor 74 are for blocking direct current, and the impedance thereof is extremely small at the operating frequency, that is, a large electrostatic capacitance. Has capacity.
[0018]
FIG. 2 shows an extracted configuration of the preceding phase shift circuit 10L shown in FIG. The phase-shift circuit 10L in the previous stage shown in the figure includes an FET 12 whose gate is connected to the input terminal 22, an inductor 17 and a resistor 16 connected in series between the source and drain of the FET 12, the drain of the FET 12, and a positive power source. And a resistor 18 connected between the source of the FET 12 and the ground.
[0019]
In the phase shift circuit 10L having such a configuration, an antenna coil such as an AM receiver or an FM receiver is used as the inductor 17. Further, the resistance values of the two resistors 20 and 18 connected to the source and drain of the FET 12 shown in FIG. 2 are set to be approximately equal.
[0020]
The resistor 26 in the phase shift circuit 10L shown in FIG. 1 is for setting the gate potential of the FET 12. The capacitor 13 inserted between the resistor 16 and the drain of the FET 12 is for DC current blocking, and its impedance is set to be extremely small at the operating frequency, that is, has a large capacitance.
[0021]
When a predetermined AC signal is input to the input terminal 22 shown in FIG. 2, that is, when a predetermined AC voltage (input voltage) is applied to the gate of the FET 12, an AC voltage in phase with the input voltage is applied to the source of the FET 12. On the other hand, an alternating voltage having the same amplitude as that of the voltage appearing at the source appears in the drain of the FET 12 in the opposite phase to the input voltage. Let Ei be the amplitude of the AC voltage appearing at the source and drain.
[0022]
A series circuit (LR circuit) composed of an inductor 17 and a resistor 16 is connected between the source and drain of the FET 12. Therefore, a signal obtained by synthesizing each of the voltages appearing at the source and drain of the FET 12 via the inductor 17 or the resistor 16 is output from the output terminal 24.
[0023]
FIG. 3 is a vector diagram showing the relationship between the input / output voltage of the preceding phase shift circuit 10L and the voltage appearing in the inductor or the like. Assuming that the potential difference between the connection point of the resistor 16 and the inductor 17 and the ground level is taken out as the output voltage Eo, the output voltage Eo starts from the center point in the semicircle shown in FIG. 3, and the voltage VR1 and the voltage VL1. Can be represented by a vector whose end point is one point on the circumference where the two intersect with each other, the size of which is equal to the radius Ei of the semicircle. Moreover, even if the frequency of the input signal changes, the end point of this vector only moves on the circumference, so that a stable output whose output amplitude does not change according to the frequency can be obtained.
[0024]
As apparent from FIG. 3, since the voltage VR1 and the voltage VL1 intersect at right angles on the circumference, the phase difference between the input voltage applied to the gate of the FET 12 and the voltage VR1 is theoretically the frequency ω. As 0 changes from 0 to ∞, it changes from 0 ° to 90 °. The phase shift amount φ1 of the entire phase shift circuit 10L is twice that, and varies from 0 ° to 180 ° depending on the frequency.
[0025]
Similarly, FIG. 4 shows an extracted configuration of the subsequent phase shift circuit 30C shown in FIG. The latter-stage phase shift circuit 30C shown in the figure includes an FET 32 whose gate is connected to the input terminal 42, a capacitor 34 and a variable resistor 36 connected in series between the source and drain of the FET 32, and a drain and a positive electrode of the FET 32. The resistor 38 is connected between the power source and the resistor 40 is connected between the source of the FET 32 and the ground. Similar to the phase shift circuit 10C, the resistance values of the two resistors 40 and 38 connected to the source and drain of the FET 32 shown in FIG. 4 are set to be approximately equal.
[0026]
The resistor 46 in the phase shift circuit 30C shown in FIG. 1 is for applying an appropriate bias voltage to the FET 32, and the capacitor 48 provided between the phase shift circuits 30C and 10L has a phase shift circuit 30C. This is for blocking direct current from the output of the circuit 10L, and only the alternating current component is input to the phase shift circuit 30C.
[0027]
When a predetermined AC signal is input to the input terminal 42 shown in FIG. 4, that is, when a predetermined AC voltage (input voltage) is applied to the gate of the FET 32, an AC having the same phase as this input voltage is applied to the source of the FET 32. On the other hand, an alternating voltage having the same amplitude as the voltage appearing at the source appears in the drain of the FET 32. Let Ei be the amplitude of the AC voltage appearing at the source and drain.
[0028]
A series circuit including a capacitor 34 and a variable resistor 36 is connected between the source and drain of the FET 32. Therefore, a signal obtained by synthesizing the voltages appearing at the source and drain of the FET 32 via the capacitor 34 or the variable resistor 36 is output from the output terminal 44.
[0029]
FIG. 5 is a vector diagram showing the relationship with the voltage appearing in the capacitor and the like of the subsequent phase shift circuit 30C. Assuming that the potential difference between the connection point of the variable resistor 36 and the capacitor 34 and the ground level is taken out as the output voltage Eo, the output voltage Eo starts at the center point in the semicircle shown in FIG. It can be represented by a vector whose end point is one point on the circumference where VC2 intersects, and its size is equal to the radius Ei of the semicircle. Moreover, even if the frequency of the input signal changes, the end point of this vector only moves on the circumference, so that a stable output whose output amplitude does not change according to the frequency can be obtained.
[0030]
Further, as apparent from FIG. 5, since the voltage VR2 and the voltage VC2 intersect at right angles on the circumference, the phase difference between the input voltage applied to the gate of the FET 32 and the voltage VR2 is theoretically the frequency ω. Changes from 90 ° to 0 ° as 0 changes from 0 to ∞. The phase shift amount φ2 of the entire phase shift circuit 30C is twice that and changes from 180 ° to 0 ° depending on the frequency.
[0031]
In this manner, the phase is shifted by a predetermined amount in each of the two phase shift circuits 10L and 30C. Moreover, as shown in FIGS. 3 and 5, the total phase shift amount is 360 ° by the whole of the two phase shift circuits 10L and 30C at a predetermined frequency. At this time, the two phase shift circuits 10L and 30C By setting the loop gain of the feedback loop formed by the circuit 160 and the feedback resistor 70 to 1 or less, the tuning operation for extracting only the predetermined frequency component described above from the signal input to a part of the feedback loop is performed. Is called.
[0032]
In the tuning circuit 1 shown in FIG. 1, since an antenna coil is used as the inductor 17 included in the feedback loop, the inductor 17 functions as a voltage source when a broadcast wave or the like reaches the antenna coil. Equivalently, it can be considered that an AC signal generated by this voltage source is input to a part of the feedback loop.
[0033]
FIG. 6 is a diagram showing an equivalent circuit corresponding to a part of the tuning circuit shown in FIG. In the figure, the inductor 17 in the phase shift circuit 10L shown in FIG. 1 is separated into a portion that functions as a simple inductor 17 'and a portion that functions as a signal source. Specifically, it can be considered that a predetermined AC voltage is generated at both ends of the inductor by an AC signal input from the voltage source 76 connected to the outside of the feedback loop. The predetermined AC signal is input to the phase shift circuit 10L through the variable resistor 74 and the capacitor 73.
[0034]
Therefore, equivalently, the signal fed back through the resistor 70 and the signal generated by the signal source 76 are added, and the added signal is input to the preceding phase shift circuit 10L and flows in the closed loop.
[0035]
FIG. 7 shows a case where the configuration of the tuning circuit 1 shown in FIG. 1 is partially replaced with the equivalent configuration shown in FIG. 6, and includes two phase shift circuits 10L and 30C, a non-inverting circuit 50, and a split circuit. FIG. 9 is a system diagram in which the entire voltage circuit 160 is replaced with a circuit having a transfer function K1, and a feedback resistor 70 having a resistance R0 in parallel with a circuit having a transfer function K1 is a resistance value (n times the feedback resistor 70 in series) An input resistor 74 having nR0) is connected. FIG. 8 is a system diagram in which the system shown in FIG. 7 is converted by Miller's theorem, and the transfer function A of the entire system after conversion is
A = Vo / Vi = K1 / {n (1-K1) +1} (1)
It can be expressed as
[0036]
By the way, the transfer function K2 of the preceding phase shift circuit 10L is the time constant of the LR circuit comprising the inductor 17 and the resistor 16 as T ₁ (If the inductance of the inductor 17 is L and the resistance value of the resistor 16 is R, T ₁ = L / R)
K2 = a ₁ (1-T ₁ s) / (1 + T ₁ s) (2)
It becomes. Where s = jω, a ₁ Is the gain of the phase shift circuit 10L and is a value less than one.
[0037]
Further, the transfer function K3 of the phase shift circuit 30C at the subsequent stage represents the time constant of the CR circuit composed of the capacitor 34 and the variable resistor 36 as T ₂ (When the resistance value of the variable resistor 36 is R and the capacitance of the capacitor 34 is C, T ₂ = CR)
K3 = -a ₂ (1-T ₂ s) / (1 + T ₂ s) (3)
It becomes. Where a ₂ Is the gain of the phase shift circuit 30C and is a value less than one.
[0038]
Further, the gain of the voltage dividing circuit 160 is set to a _Three (≦ 1), and in order to compensate for the attenuation of the signal amplitude by the phase shift circuits 10L and 30C and the voltage dividing circuit 160, the gain of the non-inverting circuit 50 is set to 1 / a ₁ a ₂ a _Three Then, the total transfer function K1 when the phase shift circuits 10L and 30C, the non-inverting circuit 50, and the voltage dividing circuit 160 are connected in cascade is
K1 =-{1+ (Ts) ² -2Ts} / {1+ (Ts) ² + 2Ts} (4)
It becomes. In order to simplify the calculation, the time constant T of each phase shift circuit ₁ , T ₂ Both are T. Substituting this equation (4) into the above equation (1),

It becomes.
[0039]
According to the equation (5), it can be seen that when ω = 0 (DC region), A = −1 / (2n + 1), and the maximum attenuation is given. Further, it can be seen that even when ω = ∞, A = −1 / (2n + 1), which gives the maximum attenuation. Further, the tuning point of ω = 1 / T (in general, since the time constant of each phase shift circuit is different, ω = 1 / √ (T ₁ ・ T ₂ )) Is A = 1 and is not related to the resistance ratio n of the resistors 70 and 74 shown in FIG. 1, and as shown in FIG. 9, the tuning bandwidth (ie, Q) and the maximum attenuation are obtained. It can be seen that operates as a bandpass filter that can be arbitrarily set.
[0040]
In the tuning circuit 1 described above, the inductor 17 included in the preceding phase shift circuit 10L is formed by an antenna coil. Therefore, various received signals such as broadcast waves can be directly taken into the tuning circuit 1, and the conventional technique An indispensable variable condenser is no longer necessary. Therefore, the entire tuning circuit 1 excluding the antenna coil can be formed on the semiconductor substrate, which is suitable for integration.
[0041]
Further, by changing the resistance value of the variable resistor 36 included in the phase shift circuit 30C at the subsequent stage of the tuning circuit 1, the frequency at which the total phase shift amount when making a round of the closed loop becomes 360 ° can be changed. Therefore, the center frequency (tuning frequency) of the tuning circuit 1 can be arbitrarily changed, and the receiver can be configured without necessarily using the superheterodyne system as in the conventional art. This eliminates the need for an intermediate frequency transformer, a local oscillation transformer, and the like, which are indispensable in a superheterodyne receiver, and makes it possible to integrally form the entire tuning mechanism and most of the receiver on a semiconductor substrate.
[0042]
Further, the tuning bandwidth, that is, the Q of the band-pass filter can be varied by changing the resistance value of the variable resistor 74 connected to the input side of the preceding phase shift circuit 10L. Thereby, in the receiver configured using the tuning circuit 1, when interference occurs, the tuning bandwidth is narrowed by adjusting the resistance value of the variable resistor 74 to prevent interference, and conversely, when interference is low. By adjusting the resistance value of the variable resistor 74, it becomes possible to widen the tuning bandwidth and faithfully reproduce the received signal, and an optimum receiver can be designed according to the interference state.
[0043]
In the tuning circuit described above, each phase shift circuit is configured using FETs, but each phase shift circuit may be configured using bipolar transistors. Using a bipolar transistor reduces the signal amplitude attenuation when passing through each phase shift circuit compared to using an FET, so the amplification of the non-inverting circuit and the phase inverting circuit in the subsequent stage should be reduced. Can do. However, if a bipolar transistor is provided in the subsequent phase shift circuit, the input impedance of the bipolar transistor is low, so the phase shift amount of the previous phase shift circuit may change. For this reason, it is more desirable to provide a bipolar transistor in the preceding phase shift circuit in order to reduce the attenuation of the signal amplitude, and to provide an FET in the subsequent phase shift circuit in order to obtain a high input impedance.
[0044]
[Second Embodiment]
FIG. 10 is a circuit diagram showing the configuration of the tuning circuit according to the second embodiment. The phase shift circuits 10L and 30C at the front stage and the rear stage of the tuning circuit 1 shown in FIG. 1 are replaced with phase shift circuits 30L and 10C, respectively. It has a configuration.
[0045]
A previous phase shift circuit 30L shown in FIG. 10 is obtained by replacing the CR circuit composed of the capacitor 34 and the variable resistor 36 in the phase shift circuit 30C shown in FIG. 1 with an LR circuit composed of the resistor 35 and the inductor 37. The inductor 37 is formed using an antenna coil, and the relationship between the input and output voltages of the phase shift circuit 30L is the same as the relationship between the input and output voltages of the phase shift circuit 30C.
[0046]
Similarly, the latter-stage phase shift circuit 10C illustrated in FIG. 10 replaces the LR circuit including the inductor 17 and the resistor 16 in the phase shift circuit 10L illustrated in FIG. 1 with a CR circuit including the variable resistor 15 and the capacitor 14. It is a thing. The relationship between the input / output voltages of the phase shift circuit 10C is the same as the relationship with the input / output voltages of the phase shift circuit 10L.
[0047]
Thus, the phase shift circuits 30L and 10C in the tuning circuit 1A are equivalent to the two phase shift circuits 10L and 30C in the tuning circuit 1 shown in FIG. 1, and the antenna coil is included in the previous phase shift circuit 30L. Since the same is true of including the inductor 37 configured by the above, the same effect as the tuning circuit 1 shown in FIG. 1 can be obtained.
[0048]
[Third Embodiment]
The tuning circuits 1 and 1A of the first embodiment described above are performing a predetermined tuning operation at a frequency at which the total amount of phase shift by the two phase shift circuits constituting each tuning circuit is 360 °. Predetermined tuning amplification may be performed at a frequency at which the total amount of phase shift by the two phase shift circuits is 180 °.
[0049]
FIG. 11 is a circuit diagram showing a detailed configuration of the tuning circuit 1B of the third embodiment. The tuning circuit 1B shown in the figure includes two phase shift circuits 10L and 10C that perform a total phase shift of 180 ° at a predetermined frequency, and a phase inversion circuit that further inverts the phase of the output signal of the subsequent phase shift circuit 10C. 80, a feedback resistor 70, and a variable resistor 74.
[0050]
The phase shift circuit 10L of the previous stage has the detailed configuration and the phase relationship of the input / output signals as described with reference to FIGS. 2 and 3. For example, the time constant of the LR circuit including the resistor 16 and the inductor 17 is set to T ₁ Then, ω = 1 / T ₁ At a nearby frequency, the phase shift amount φ1 is approximately 90 °.
[0051]
Further, the relationship between the input and output voltages of the subsequent phase shift circuit 10C is the same as the relationship between the input and output voltages of the previous phase shift circuit 10L shown in FIG. 1, for example, a CR circuit comprising a capacitor 14 and a variable resistor 15. The time constant of T ₁ ′, Ω = 1 / T ₁ At a frequency in the vicinity of ', the phase shift amount φ1' is approximately 90 °.
[0052]
Thus, the sum of the phase shift amounts of the two phase shift circuits 10L and 10C as a whole becomes φ1 + φ1 ′ = 180 ° at a predetermined frequency.
[0053]
Further, the phase inversion circuit 80 includes an FET 82 in which a resistor 84 is connected between the drain and the positive power source, and a resistor 86 is connected between the source and the ground, and a resistor 88 that applies a predetermined bias voltage to the gate of the FET 82. It is comprised including. When an AC signal is input to the gate of the FET 82, a reverse-phase signal whose phase is inverted is output from the drain of the transistor 82. The phase inversion circuit 80 has a predetermined amplification degree determined by the resistance ratio of the two resistors 84 and 86.
[0054]
Thus, at a predetermined frequency, the phase is shifted by 180 ° by the two phase shift circuits 10L and 10C, and the phase is inverted by the phase inverting circuit 80 connected to the subsequent stage. The total amount is 360 °.
[0055]
Further, the output of the phase inverting circuit 80 is taken out from the output terminal 92 as the output of the tuning circuit 1B, and the voltage obtained by dividing the output by the voltage dividing circuit 160 is fed through the feedback resistor 70 to the phase shift circuit 10L of the preceding stage. Returned to the input side.
[0056]
As described above, the inductor 17 formed of the antenna coil is included in one phase shift circuit 10L, and the output of the phase inversion circuit 80 is fed back to the input side of the previous phase shift circuit 10L via the feedback resistor 70. A predetermined tuning operation can be performed by setting the loop gain of the loop to 1 or less. Therefore, like the tuning circuit 1 shown in FIG. 1 and the like, the tuning frequency can be arbitrarily changed, and there is a feature that a variable capacitor is unnecessary and suitable for integration.
[0057]
[Fourth Embodiment]
The tuning circuit shown in FIG. 11 shows an example in which the phase shift circuits 10L and 10C are connected in cascade. However, as shown in FIG. 12, the tuning operation can be performed even when the phase shift circuits 30L and 30C are connected in cascade. it can.
[0058]
The total phase shift amount of the two phase shift circuits 30L and 30C is φ2 ′ + φ2 = 180 ° at a predetermined frequency, and the phase is shifted by 180 ° by the two phase shift circuits 30L and 30C at the predetermined frequency. Further, the phase is inverted by the phase inversion circuit 80 connected to the subsequent stage, and the total phase shift amount of these three circuits becomes 360 °.
[0059]
[Fifth Embodiment]
In the various tuning circuits described above, the example in which the inductor formed by the antenna coil is provided in the phase shift circuit has been described. However, the tuning circuit is configured using the primary coil and the secondary coil of the bar antenna of the AM receiver or the like. You can also
[0060]
FIG. 13 is a circuit diagram showing the detailed configuration of the fifth embodiment of the tuning circuit. The tuning circuit 1D shown in the figure is configured by cascading a phase shift circuit 110L, a phase shift circuit 30C, and a non-inverting circuit 80. The phase shift circuit 110L includes an LR circuit including a resistor 16 and an inductor 117A. It is out. The inductor 117A is configured using a primary coil of a bar antenna such as an AM receiver, and a secondary coil 117B is magnetically coupled to the primary coil, and an output of a tuning circuit is output from both ends of the secondary coil 117B. That is, a tuning signal is extracted. Further, the output of the subsequent phase shift circuit 30C in the tuning circuit 1 shown in FIG. 13 is fed back to the input side of the previous phase shift circuit 110L without going through the voltage dividing circuit. Other configurations are common to the tuning circuit shown in FIG.
[0061]
FIG. 14 is a block diagram of an AM receiver including the tuning circuit shown in FIG. The AM receiver shown in the figure includes the tuning circuit 1D, the AM detection circuit 2, the low frequency amplification circuit 3 and the speaker 4 shown in FIG. 13, and the AM detection circuit 2 includes a secondary circuit in the tuning circuit 1. A tuning signal output from the coil is input.
[0062]
In the AM receiver shown in FIG. 14, when an AM wave is received by the bar antenna 17 included in the tuning circuit, AC voltages having various frequencies included in the AM wave are formed at both ends of the inductor 117A composed of the primary coil of the bar antenna 117. Will occur. Among the AC signals of various frequencies, components whose total phase shift amount of the two phase shift circuits 110L and 30C is other than 360 ° are attenuated by being fed back through the closed loop of the tuning circuit 1D. As a result, only frequency components with a total phase shift amount of 360 ° are selected and output as a tuning signal from the secondary coil 117B. This tuning signal is AM detected by the AM detection circuit 2 and converted into an audio signal, then amplified by the low frequency amplifier circuit 3 and output from the speaker 4.
[0063]
In this manner, since the inductor 117A in the preceding phase shift circuit 110L is configured by the primary coil of the bar antenna 117, various received signals such as broadcast waves received by the bar antenna 117 can be directly taken into the tuning circuit 1D. This eliminates the need for a variable condenser that was indispensable in the past. Therefore, the entire tuning circuit 1D excluding the bar antenna 117 can be formed on the semiconductor substrate, and downsizing and cost reduction can be achieved.
[0064]
Further, since the tuning signal is taken out from the secondary coil 117B magnetically coupled to the primary coil, the DC component can be cut, and the connection with the circuit at the next stage is facilitated. When the tuning circuit 1 shown in FIG. 13 was actually assembled and the output waveform was measured, noise could be reduced compared to the case where the tuning signal was directly extracted from a part of the closed loop.
[0065]
Further, for example, when tuning is performed by an LC resonance circuit as in a conventional AM receiver, the inductance of the bar antenna 117 has to be sufficiently increased due to restrictions on the capacitance of the variable capacitor used and the variable range. . On the other hand, in the tuning circuit 1 of the present embodiment, the inductance is combined with the resistance, so that the inductance of the inductor can be set freely to some extent. Therefore, the inductance of the bar antenna can be made smaller than before, and the entire receiver can be downsized.
[0066]
In FIG. 14, the example in which the tuning circuit shown in FIG. 1 is applied to an AM receiver has been described. However, the tuning circuit can also be applied to an FM receiver. In that case, the AM detection circuit shown in FIG. 14 may be replaced with an FM detection circuit.
[0067]
[Sixth Embodiment]
FIG. 13 illustrates an example in which the inductor in the preceding phase shift circuit shown in FIG. 1 is replaced with the primary coil of the bar antenna. Similarly, the tuning circuits 1A, 1B, For each of 1C, the inductor in the preceding phase shift circuit may be replaced with the primary coil of the bar antenna, and the tuning output may be extracted from the secondary coil of the bar antenna.
[0068]
15, 16, and 17 are circuit diagrams showing examples in which the inductor in the preceding phase shift circuit shown in FIGS. 10, 11, and 12 is replaced with the primary coil of the bar antenna and the voltage dividing circuit 160 is removed. It is.
[0069]
15, 16, and 17, since the tuning signal is extracted from the secondary coil magnetically coupled to the primary coil, the DC component can be cut, and the connection to the circuit at the next stage is facilitated. .
[0070]
[Other Embodiments]
The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the gist of the present invention.
[0071]
For example, the various tuning circuits described above are composed of two phase shift circuits and a non-inversion circuit, or two phase shift circuits and a phase inversion circuit, focusing on the phase shift. A predetermined tuning operation is performed by setting the total phase shift amount to 360 ° at a predetermined frequency. Therefore, when focusing only on the phase shift amount, there is a certain degree of freedom in which of the two phase shift circuits is used in the preceding stage, or in what order the three circuits are connected, and the connection order as necessary. Can be decided.
[0072]
Further, in the various tuning circuits described above, an inductor constituted by an antenna coil or a primary coil of the bar antenna 117 is provided in the preceding phase shift circuit, but the arrangement of the preceding and succeeding phase shift circuits is switched. Thus, an inductor may be provided in the subsequent phase shift circuit.
[0073]
Further, in the various tuning circuits described above, the example in which the phase shift circuit including the LR circuit and the phase shift circuit including the CR circuit are cascade-connected has been described, but two phase shift circuits including the LR circuit are included. Circuits may be connected in cascade.
[0074]
In the various tuning circuits described above, the variable resistor is provided only in one of the phase shift circuits, but the variable resistor may be provided in both of the phase shift circuits. For example, the resistor 16 shown in FIG. 1 may be replaced with a variable resistor. If variable resistors are provided in both phase shift circuits, the total amount of phase shift by the two phase shift circuits can be increased, so that the variable range of the tuning frequency of the entire tuning circuit can be expanded.
[0075]
In the various tuning circuits shown up to the fourth embodiment, the voltage dividing circuit is connected to the output side of the subsequent phase shift circuit. However, this voltage dividing circuit is omitted, and the subsequent phase shift circuit. May be directly fed back to the input side of the preceding phase shift circuit.
[0076]
Note that the variable resistors (for example, the variable resistor 36 in FIG. 1) in the various tuning circuits described above can be configured by, for example, FETs. In this case, the variable resistor may be configured by one FET, but one variable resistor may be configured by connecting a p-channel FET and an n-channel FET in parallel. In this way, by configuring the variable resistor by combining two FETs, it is possible to improve the nonlinear region of the FETs, so that the distortion of the tuning output can be reduced.
[0077]
【The invention's effect】
As described above, the tuning circuit of the present invention operates as a bandpass filter having a predetermined tuning frequency, and the inductor included in one phase shift circuit is formed by an antenna coil. The received signal can be directly taken into the tuning circuit, eliminating the need for a variable capacitor that has been indispensable in the past. Therefore, the entire tuning circuit excluding the inductor can be formed on the semiconductor substrate, which is suitable for integration.
[0078]
Further, by changing the resistance value of the variable resistor included in at least one of the phase shift circuits, the frequency at which the total amount of phase becomes 360 ° when the loop of the tuning circuit is made can be changed. The receiver can be configured without necessarily using the superheterodyne system as in the prior art. This eliminates the need for an intermediate frequency transformer, a local oscillation transformer, and the like, which are indispensable in a superheterodyne receiver, and makes it possible to integrally form the entire tuning mechanism and most of the receiver on a semiconductor substrate.
[0079]
Further, since the tuning bandwidth, that is, the Q of the bandpass filter can be varied by changing the resistance value of at least one of the resistor connected to the input side of the preceding phase shift circuit or the feedback resistor, for example, the tuning circuit In a receiver configured using this method, when interference occurs, the tuning bandwidth can be narrowed to prevent interference, and when interference is low, the tuning bandwidth can be widened to faithfully reproduce the received signal. Therefore, an optimum receiver can be designed according to the interference state.
[0080]
In addition, since a tuning signal is output from a secondary coil such as a bar antenna, a direct current component included in the tuning signal can be removed, and connection with a circuit at the next stage is facilitated.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a tuning circuit according to a first embodiment.
2 is a circuit diagram showing a configuration of a preceding phase shift circuit shown in FIG. 1; FIG.
3 is a vector diagram showing a relationship between input / output voltages of the phase shift circuit shown in FIG. 2 and voltages appearing in an inductor or the like. FIG.
4 is a circuit diagram showing a configuration of a subsequent phase shift circuit shown in FIG. 1; FIG.
5 is a vector diagram showing a relationship between input / output voltages of the phase shift circuit shown in FIG. 4 and voltages appearing in a capacitor or the like. FIG.
6 is a diagram showing an equivalent circuit corresponding to a part of the tuning circuit shown in FIG. 1; FIG.
FIG. 7 is a diagram in which two phase shift circuits and a voltage dividing circuit in the tuning circuit are replaced with a circuit having a predetermined transfer function.
8 is a diagram obtained by converting the circuit shown in FIG. 7 by Miller's theorem.
FIG. 9 is a characteristic diagram of the tuning circuit shown in FIG. 1;
FIG. 10 is a circuit diagram showing a configuration of a tuning circuit according to a second embodiment.
FIG. 11 is a circuit diagram showing a configuration of a tuning circuit according to a third embodiment.
FIG. 12 is a circuit diagram showing a configuration of a tuning circuit according to a fourth embodiment.
FIG. 13 is a circuit diagram showing a configuration of a tuning circuit according to a fifth embodiment.
14 is a block diagram of an AM receiver including the tuning circuit shown in FIG.
15 is a circuit diagram showing an example in which the inductor in the preceding phase shift circuit shown in FIG. 10 is replaced with a primary coil of a bar antenna.
16 is a circuit diagram showing an example in which the inductor in the preceding phase shift circuit shown in FIG. 11 is replaced with a primary coil of a bar antenna.
17 is a circuit diagram showing an example in which the inductor in the preceding phase shift circuit shown in FIG. 12 is replaced with a primary coil of a bar antenna.
[Explanation of symbols]
1 Tuning circuit
10L, 30C phase shift circuit
12, 32 FET
13, 34 Capacitor
16, 18, 20, 38, 40 Resistance
17 Inductor
36, 74 Variable resistance
70 Feedback resistance
160 Voltage divider circuit

Claims (13)

An all-pass type that includes a non-inverting circuit that amplifies the input AC signal at a predetermined amplification level and outputs it in the same phase, and conversion means that converts the input AC signal into an in-phase and reverse-phase AC signal and outputs the same. With two phase shift circuits,
One of the two phase shift circuits includes an LR circuit including an inductor formed of an antenna coil and a first resistor,
The other of the two phase shift circuits includes a CR circuit composed of a capacitor and a second resistor,
A tuning circuit, wherein the two phase shift circuits and the non-inverting circuit are cascaded in a predetermined order, and the output of the final stage circuit is fed back to the input side of the first stage circuit. In claim 1,
A tuning circuit, wherein a voltage dividing circuit is inserted into a part of a closed loop formed including the two phase shift circuits, and an AC signal inputted to the voltage dividing circuit is taken out as a tuning output. A non-inverting circuit that amplifies the input AC signal with a predetermined amplification and outputs it in the same phase, and a conversion means that converts the input AC signal into an in-phase and reverse-phase AC signal and outputs them, respectively, are connected in cascade. Two phase-shift circuits that are all-pass
One of the two phase shift circuits includes an LR circuit composed of an inductor composed of a primary coil of an antenna and a first resistor, and a secondary coil magnetically coupled to the primary coil,
The other of the two phase shift circuits includes a CR circuit composed of a capacitor and a second resistor,
The two phase shift circuits and the non-inverting circuit are cascaded in a predetermined order, the output of the final stage circuit is fed back to the input side of the first stage circuit, and the tuning signal is taken out from both ends of the secondary coil A tuning circuit characterized by that. A phase inverting circuit that amplifies the input AC signal at a predetermined amplification and inverts and outputs the phase; and a conversion means that converts the input AC signal into an in-phase AC signal and an anti-phase AC signal and outputs the converted AC signal. Two phase shift circuits connected in cascade with each other, and
One of the two phase shift circuits includes an LR circuit including an inductor formed of an antenna coil and a first resistor,
The other of the two phase shift circuits includes a CR circuit composed of a capacitor and a second resistor,
A tuning circuit, wherein the two phase shift circuits and the phase inversion circuit are cascaded in a predetermined order, and the output of the final stage circuit is fed back to the input side of the first stage circuit. In claim 4,
A tuning circuit, wherein a voltage dividing circuit is inserted into a part of a closed loop formed including the two phase shift circuits, and an AC signal inputted to the voltage dividing circuit is taken out as a tuning output. A phase inverting circuit that amplifies the input AC signal at a predetermined amplification and inverts and outputs the phase; and a conversion means that converts the input AC signal into an in-phase AC signal and an anti-phase AC signal and outputs the converted AC signal. Two phase shift circuits connected in cascade with each other, and
One of the two phase shift circuits includes an LR circuit composed of an inductor composed of a primary coil of an antenna and a first resistor, and a secondary coil magnetically coupled to the primary coil,
The other of the two phase shift circuits includes a CR circuit composed of a capacitor and a second resistor,
The two phase shift circuits and the phase inversion circuit are cascaded in a predetermined order, the output of the final stage circuit is fed back to the input side of the first stage circuit, and a tuning signal is taken out from both ends of the secondary coil. A tuning circuit characterized by that. In any one of Claims 1-6,
One of the two phase shift circuits synthesizes one AC signal converted by the conversion means via one end of the LR circuit and the other AC signal via the other end of the LR circuit. Including the synthesis means of
The other of the two phase shift circuits synthesizes one AC signal converted by the conversion means via one end of the CR circuit and the other AC signal via the other end of the CR circuit. Including the synthesis means of
Each of the first and second combining means outputs a signal having a constant amplitude and only a phase shifted by a predetermined amount. In any one of Claims 1-7,
Each of the conversion means includes a transistor, and a third resistor having substantially the same resistance value is connected to the source and drain or emitter and collector of the transistor, respectively, and an AC signal is input to the gate or base of the transistor. The LR circuit or the CR circuit is connected between the source and drain of the transistor or between the emitter and collector. In any one of Claims 1-8,
A tuning circuit, wherein a tuning frequency is changed by varying a time constant of at least one of the CR circuit or the LR circuit. In claim 9,
A tuning circuit, wherein the time constant is changed by changing a resistance value of a resistor included in at least one of the CR circuit or the LR circuit. In any one of Claims 1-10,
A fourth resistor inserted in a part of a closed loop formed including the two phase shift circuits, and a fifth resistor provided for branching a part of the AC signal flowing in the closed loop; A tuning circuit comprising: a tuning bandwidth varying by varying a resistance ratio of the fourth and fifth resistors. In any one of Claims 1-11,
A tuning circuit characterized in that a tuning operation is performed without oscillation by setting a loop gain of a closed loop formed including the two phase shift circuits to 1 or less. In any one of Claims 1-12,
A tuning circuit, wherein the components excluding the inductor are integrally formed on a semiconductor substrate.

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