JPH04343503A - Fm detector - Google Patents
Fm detectorInfo
- Publication number
- JPH04343503A JPH04343503A JP11521791A JP11521791A JPH04343503A JP H04343503 A JPH04343503 A JP H04343503A JP 11521791 A JP11521791 A JP 11521791A JP 11521791 A JP11521791 A JP 11521791A JP H04343503 A JPH04343503 A JP H04343503A
- Authority
- JP
- Japan
- Prior art keywords
- voltage
- signal
- frequency
- detector
- outputs
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000003990 capacitor Substances 0.000 claims abstract description 23
- 238000001514 detection method Methods 0.000 claims abstract description 13
- 230000010355 oscillation Effects 0.000 claims description 5
- 239000000284 extract Substances 0.000 claims description 2
- 238000010586 diagram Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 2
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000009499 grossing Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
Landscapes
- Adjustment Of The Magnetic Head Position Track Following On Tapes (AREA)
Abstract
Description
【0001】0001
【産業上の利用分野】本発明は、FM検波器に関し、特
にFM放送受信機において中間周波数(IF)信号を可
聴周波数(AF)信号へ検波するFM検波器に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM detector, and more particularly to an FM detector for detecting an intermediate frequency (IF) signal into an audio frequency (AF) signal in an FM broadcast receiver.
【0002】0002
【従来の技術】一般に、FM検波器は、ラジオ放送局か
ら送信される様々な周波数を搬送波とする周波数変調(
FM)信号を受信してその一つを選択し、これと受信機
内の局部発振器とを混合して、一定の中間周波数を搬送
波とするFM信号へ変換する。これがIF信号で、その
後IF信号を検波器内部で定まる固有の周波数(以下内
部周波数という)と比較し、周波数差を電圧として取り
出す事により、AF信号を出力する。2. Description of the Related Art In general, an FM detector uses frequency modulation (frequency modulation) using various frequencies transmitted from radio broadcasting stations as carrier waves.
FM) signals, selects one of them, mixes it with a local oscillator in the receiver, and converts it into an FM signal with a fixed intermediate frequency as a carrier wave. This is the IF signal, and the IF signal is then compared with a unique frequency determined inside the detector (hereinafter referred to as internal frequency), and the frequency difference is extracted as a voltage, thereby outputting the AF signal.
【0003】このようなFM検波器では、内部周波数が
搬送波の周波数とずれると、AF信号の歪率が悪化して
しまうので、内部周波数を搬送波の周波数と一致させる
必要がある。In such an FM detector, if the internal frequency deviates from the frequency of the carrier wave, the distortion rate of the AF signal deteriorates, so it is necessary to make the internal frequency coincide with the frequency of the carrier wave.
【0004】図3は、FM検波器の従来例の回路図であ
る。可変インダクタンスのコイル13は、コンデンサ1
4と並列共振回路を構成しており、この共振回路で定ま
る内部周波数で、発振器10が発振する。IF入力端子
1から入力されるIF信号と、発振器10からの内部周
波数出力とをFM検波回路2で比較することにより、A
F出力端子3へAF信号を出力する。FIG. 3 is a circuit diagram of a conventional FM detector. The variable inductance coil 13 is connected to the capacitor 1
4 constitutes a parallel resonant circuit, and the oscillator 10 oscillates at an internal frequency determined by this resonant circuit. By comparing the IF signal input from the IF input terminal 1 and the internal frequency output from the oscillator 10 in the FM detection circuit 2,
Outputs the AF signal to the F output terminal 3.
【0005】この場合、コイル13のインダクタンスを
調節することにより、内部周波数と搬送波の周波数と一
致させてAF信号を、最適点へ設定することができる。[0005] In this case, by adjusting the inductance of the coil 13, the AF signal can be set to the optimum point by making the internal frequency match the frequency of the carrier wave.
【0006】[0006]
【発明が解決しようとする課題】上述の従来のFM検波
器では、AF信号を最適点に設定する為に、個々のFM
検波器毎に可変コイル13を調節する作業が必要であり
、セット組立時の調整工数が大きく能率が低下し、また
このようにして最適点に設定してもその後の局部発振器
10の周波数の変動などによる搬送波の周波数の変動に
対しても、AF出力の歪率が悪化するという問題点があ
った。[Problems to be Solved by the Invention] In the conventional FM detector described above, in order to set the AF signal at the optimum point, it is necessary to
It is necessary to adjust the variable coil 13 for each detector, which increases the number of adjustment steps during set assembly and reduces efficiency.Also, even if the optimum point is set in this way, subsequent fluctuations in the frequency of the local oscillator 10 occur. There is also a problem in that the distortion rate of the AF output deteriorates due to variations in the frequency of the carrier wave caused by such factors.
【0007】本発明の目的は、このような問題を解決し
、可変コイルを不要として調整工数を少くし、内部周波
数の周波数変動にも対応して歪率を改善したFM検波器
を提供することにある。An object of the present invention is to provide an FM detector that solves these problems, eliminates the need for a variable coil, reduces the number of adjustment steps, and improves distortion by responding to frequency fluctuations in the internal frequency. It is in.
【0008】[0008]
【課題を解決するための手段】本発明のFM検波器の構
成は、コイルと可変コンデンサとを並列接続した共振回
路と、この共振回路の共振周波数で発振する発振回路と
、この発振回路の出力信号と周波数変調された中間周波
信号とを受けて両信号の周波数差を可聴周波数信号とし
て出力するFM検波回路とを含むFM検波器において、
前記可聴周波数信号の動作の中心電圧となる動作点を直
流電圧として取出す動作点検出回路と、前記動作点の基
準となる基準電圧を出力する基準電圧源と、前記動作点
電圧と前記基準電圧とを受けてこれら電圧の差に相当す
る差信号を出力して前記可変コンデンサに供給する差動
増幅器とを備え、前記可変コンデンサは外部からの制御
によりその容量値が変化するものであることを特徴とす
る。[Means for Solving the Problems] The configuration of the FM detector of the present invention includes a resonant circuit in which a coil and a variable capacitor are connected in parallel, an oscillation circuit that oscillates at the resonant frequency of this resonant circuit, and an output of this oscillation circuit. An FM detector including an FM detection circuit that receives a signal and a frequency-modulated intermediate frequency signal and outputs a frequency difference between the two signals as an audible frequency signal,
an operating point detection circuit that extracts an operating point that is a center voltage of the operation of the audio frequency signal as a DC voltage; a reference voltage source that outputs a reference voltage that is a reference for the operating point; and a differential amplifier that outputs a difference signal corresponding to the difference between these voltages and supplies it to the variable capacitor, and the variable capacitor is characterized in that its capacitance value is changed by external control. shall be.
【0009】[0009]
【実施例】図1は本発明の一実施例のブロック図である
。図において、4は動作点検出端子、5は大容量コンデ
ンサ、6は基準電圧源、7は差動増幅器、8はコイル、
9は可変型コンデンサ、11はバッファ、15は動作点
検出回路である。差動増幅器7の出力電圧をVとして、
これがコンデンサ9へ入力されているとすると、コンデ
ンサ9の値はVの関数として、C=C(V)のように表
わされ、コイル8のインダクタンスをLとすると、並列
共振回路の共振周波数f0 は次式(1)のようになる
。DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, 4 is an operating point detection terminal, 5 is a large capacitor, 6 is a reference voltage source, 7 is a differential amplifier, 8 is a coil,
9 is a variable capacitor, 11 is a buffer, and 15 is an operating point detection circuit. Assuming that the output voltage of the differential amplifier 7 is V,
Assuming that this is input to the capacitor 9, the value of the capacitor 9 is expressed as a function of V as C=C(V), and if the inductance of the coil 8 is L, then the resonant frequency f0 of the parallel resonant circuit is expressed as the following equation (1).
【0010】
f0 =1/2π{LC(V)}1/2 ………(1)
また、FM検波回路2は、共振周波数f0 に対しIF
信号の周波数が高い時に正の電圧を出力し、低い時に負
の電圧を出力するものとし、コンデンサ9は差動増幅器
7の出力電圧Vに対して次式(2)の関係にあるとする
。
ここでA,Bは定数とする。[0010] f0 =1/2π{LC(V)}1/2 (1)
In addition, the FM detection circuit 2 has an IF for the resonant frequency f0.
It is assumed that a positive voltage is output when the signal frequency is high and a negative voltage is output when the signal frequency is low, and the capacitor 9 has a relationship with the output voltage V of the differential amplifier 7 as shown in the following equation (2). Here, A and B are constants.
【0011】
C(V)=A×V−B …
……(2)すると式(1)は次式(3)のようになる。C(V)=A×V-B...
...(2) Then, equation (1) becomes the following equation (3).
【0012】
f0 =X・VB/2
………(3)ただし X=1/2π(LA)1/
2 ここで仮にキャリアの周波数が、式(3)の共振
周波数f0 より高い周波数であれば、動作点は、基準
電圧より高くなる。これにより差動増幅器7の出力も高
くなるので、式(3)により、共振周波数f0 も高く
なり、動作点は、基準電圧へ近づく方向へ向う。こうし
て、常に最適ポイントで動作する様に、f0 は自動的
に変化する。[0012] f0 =X・VB/2
......(3) However, X=1/2π(LA)1/
2 Here, if the frequency of the carrier is higher than the resonance frequency f0 of equation (3), the operating point will be higher than the reference voltage. As a result, the output of the differential amplifier 7 also becomes high, so according to equation (3), the resonant frequency f0 also becomes high, and the operating point moves toward the reference voltage. In this way, f0 changes automatically so that it always operates at the optimum point.
【0013】図2は、本発明の第2の実施例の回路図で
あり、図1の外部制御型コンデンサ9を、電圧制御型コ
ンデンサ12にしたものである。この電圧制御型コンデ
ンサ12は、半導体のPN接合の接合容量を利用したコ
ンデンサで、制御電圧に対し、式(2)のような特性を
有している。FIG. 2 is a circuit diagram of a second embodiment of the present invention, in which the externally controlled capacitor 9 in FIG. 1 is replaced with a voltage controlled capacitor 12. This voltage-controlled capacitor 12 is a capacitor that utilizes the junction capacitance of a semiconductor PN junction, and has characteristics as shown in equation (2) with respect to the control voltage.
【0014】[0014]
【発明の効果】以上説明したように本発明は、FM検波
した信号を平滑した電圧を用いて、共振周波数を自動的
に調整することにより、可変コイルを調整する作業が必
要なくなり、またキャリアの変動に対し、歪率が悪化す
ることなく検波できるという効果を有する。Effects of the Invention As explained above, the present invention automatically adjusts the resonant frequency using a voltage obtained by smoothing an FM detected signal, thereby eliminating the need for adjusting the variable coil and This has the effect of being able to detect fluctuations without deteriorating the distortion rate.
【図1】本発明の一実施例の回路図。FIG. 1 is a circuit diagram of an embodiment of the present invention.
【図2】本発明の第2の実施例の回路図。FIG. 2 is a circuit diagram of a second embodiment of the present invention.
【図3】従来例のFM検波器の一例のブロック図。FIG. 3 is a block diagram of an example of a conventional FM detector.
1 IF入力端子 2 FM検波回路 3 AF出力端子 4 動作点検出端子 5 大容量コンデンサ 6 基準電圧源 7 差動増幅器 8 コイル 9 外部制御型コンデンサ 10 発振器 11 バッファ 12 電圧制御型コンデンサ 13 可変コイル 14 コンデンサ 15 動作点検出回路 1 IF input terminal 2 FM detection circuit 3 AF output terminal 4 Operating point detection terminal 5 Large capacity capacitor 6 Reference voltage source 7 Differential amplifier 8 Coil 9 Externally controlled capacitor 10 Oscillator 11 Buffer 12 Voltage controlled capacitor 13 Variable coil 14 Capacitor 15 Operating point detection circuit
Claims (3)
した共振回路と、この共振回路の共振周波数で発振する
発振回路と、この発振回路の出力信号と周波数変調され
た中間周波信号とを受けて両信号の周波数差を可聴周波
数信号として出力するFM検波回路とを含むFM検波器
において、前記可聴周波数信号の動作の中心電圧となる
動作点を直流電圧として取出す動作点検出回路と、前記
動作点の基準となる基準電圧を出力する基準電圧源と、
前記動作点電圧と前記基準電圧とを受けてこれら電圧の
差に相当する差信号を出力して前記可変コンデンサに供
給する差動増幅器とを備え、前記可変コンデンサは外部
からの制御によりその容量値が変化するものであること
を特徴とするFM検波器。Claim 1: A resonant circuit in which a coil and a variable capacitor are connected in parallel, an oscillation circuit that oscillates at the resonant frequency of the resonant circuit, and an oscillation circuit that receives an output signal of the oscillation circuit and a frequency-modulated intermediate frequency signal. An FM detector that includes an FM detection circuit that outputs a frequency difference between signals as an audio frequency signal, an operating point detection circuit that extracts an operating point that is the center voltage of the operation of the audio frequency signal as a DC voltage; a reference voltage source that outputs a reference voltage as a reference;
a differential amplifier that receives the operating point voltage and the reference voltage, outputs a difference signal corresponding to the difference between these voltages, and supplies the signal to the variable capacitor; An FM detector characterized in that the FM detector changes.
る電圧、電流または物理的要因により、その容量値を可
変できるものである請求項1記載のFM検波器。2. The FM detector according to claim 1, wherein the variable capacitor is capable of varying its capacitance value depending on an externally input voltage, current, or physical factor.
的特性が最適となる最適点の動作点の電圧値と一致した
電圧値である請求項1または2記載のFM検波器。3. The FM detector according to claim 1, wherein the reference voltage source has a voltage value that matches a voltage value at an optimal operating point where the electrical characteristics of the audio frequency signal are optimal.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP11521791A JPH04343503A (en) | 1991-05-21 | 1991-05-21 | Fm detector |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP11521791A JPH04343503A (en) | 1991-05-21 | 1991-05-21 | Fm detector |
Publications (1)
Publication Number | Publication Date |
---|---|
JPH04343503A true JPH04343503A (en) | 1992-11-30 |
Family
ID=14657265
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP11521791A Pending JPH04343503A (en) | 1991-05-21 | 1991-05-21 | Fm detector |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPH04343503A (en) |
-
1991
- 1991-05-21 JP JP11521791A patent/JPH04343503A/en active Pending
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