JPH084753Y2 - AFT circuit of television receiver - Google Patents
AFT circuit of television receiverInfo
- Publication number
- JPH084753Y2 JPH084753Y2 JP1988138924U JP13892488U JPH084753Y2 JP H084753 Y2 JPH084753 Y2 JP H084753Y2 JP 1988138924 U JP1988138924 U JP 1988138924U JP 13892488 U JP13892488 U JP 13892488U JP H084753 Y2 JPH084753 Y2 JP H084753Y2
- Authority
- JP
- Japan
- Prior art keywords
- aft
- electric field
- field strength
- control voltage
- circuit
- 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.)
- Expired - Lifetime
Links
Landscapes
- Television Receiver Circuits (AREA)
- Channel Selection Circuits, Automatic Tuning Circuits (AREA)
- Circuits Of Receivers In General (AREA)
Description
【考案の詳細な説明】 （イ） 産業上の利用分野 本考案はテレビジョン受像機のAFT回路に関する。[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to an AFT circuit of a television receiver.
（ロ） 従来の技術 テレビジョン受像機に使用されているAFT回路は、そ
の回路構成上、次のような欠点を有することが従来より
よく知られている。即ち、先ず第１に、テレビジョン信
号の受信電界強度が弱くなって、AFT検波回路への入力
が減少すると、AFT制御電圧の振幅が第３図の破線のよ
うに小さくなり、その結果、AFTの引込み範囲が狭くな
る。これを防止するには、AFT検波回路の感度を上げる
ことによって通常の電界強度時（中電界強度以上の時）
でのAFT制御電圧特性を第３図の実線から一点鎖線のよ
うに変更することが考えられるが、この方法では図中Ｐ
点でAFTロックが行なわれると云う誤動作が生じる。(B) Conventional Technology It is well known that the AFT circuit used in a television receiver has the following drawbacks due to its circuit configuration. That is, first of all, when the received electric field strength of the television signal becomes weak and the input to the AFT detection circuit decreases, the amplitude of the AFT control voltage becomes small as shown by the broken line in FIG. The pulling range of is narrowed. To prevent this, increase the sensitivity of the AFT detection circuit at normal electric field strength (when the electric field strength is medium or higher).
It is conceivable to change the AFT control voltage characteristics in Fig. 3 from the solid line in Fig. 3 to the alternate long and short dash line.
At that point, a malfunction occurs that AFT lock is performed.
また、受信電界強度が更に弱くなって所謂微弱電界強
度状態になると、AFTの検波回路に多くのノイズが入力
されることになり、しかも、そのノイズの周波数分布の
アンバランスから、AFT制御電圧特性が第４図の破線の
ように全体的に持ち上がり、AFTのロック状態となる周
波数が正規の周波数ｆ。からずれる（Ｑ点）と云う問題
があった。Also, when the received electric field strength becomes weaker and becomes a so-called weak electric field strength state, a lot of noise is input to the AFT detection circuit, and moreover, due to the imbalance in the frequency distribution of the noise, the AFT control voltage characteristic Is raised as shown by the broken line in FIG. 4, and the frequency at which the AFT is locked is the normal frequency f. There was a problem of slipping (point Q).
このため、前者即ち弱電界強度状態での誤動作に対し
ては、実開昭59-95142号公報［H03J7/02］や特公昭59-2
7143号公報［H04N5/50］に示されるように、AFT検波回
路の90°移相回路にトラップ回路を付設したり、一定値
以上または以下のAFT制御電圧をクリップすることによ
って、AFT制御電圧特性に不要なロック点が生じないよ
うにしている。しかしながら、斯る従来例では、後者の
誤動作即ち微弱電界強度状態でのAFT制御電圧特性のず
れによる誤動作は全く解消できなかった。For this reason, the former, that is, the malfunction in the weak electric field strength state, is disclosed in Japanese Utility Model Laid-Open No. 59-95142 [H03J7 / 02] and Japanese Patent Publication No. 59-2.
As shown in Japanese Patent No. 7143 [H04N5 / 50], by attaching a trap circuit to the 90 ° phase shift circuit of the AFT detection circuit or clipping the AFT control voltage above or below a certain value, the AFT control voltage characteristic This prevents unnecessary lock points from occurring. However, in the conventional example, the latter malfunction, that is, the malfunction due to the shift of the AFT control voltage characteristic in the weak electric field strength state, cannot be completely eliminated.
（ハ） 考案が解決しようとする課題 本考案は上記の点に留意してなされたものであり、弱
電界強度時だけでなく微弱電界強度状態での誤動作をも
防止し得るテレビジョン受像機のAFT回路を提供しよう
とするものである。(C) Problems to be solved by the present invention The present invention has been made with the above points in mind, and is intended for use in television receivers that can prevent malfunctions not only during weak electric field strength but also under weak electric field strength. It is intended to provide an AFT circuit.
（ニ） 課題を解決するための手段 本考案では、テレビジョン信号の受信電界強度の検出
出力に応じてAFT制御電圧特性を切換えるようにしたも
のであり、そして、特に弱電界強度状態ではAFT制御電
圧が増大するように切換えられ、それよりも更に電界強
度の低い微弱電界強度状態ではAFT制御電圧がAFT動作停
止時の一定値に切換えられるようにしている。(D) Means for Solving the Problems In the present invention, the AFT control voltage characteristic is switched according to the detection output of the received electric field strength of the television signal, and especially in the weak electric field strength state. The voltage is switched so as to increase, and in a weak electric field strength state where the electric field strength is lower than that, the AFT control voltage is switched to a constant value when the AFT operation is stopped.
（ホ） 作用 上記構成に依れば、弱電界強度には、AFT制御電圧の
低下が補正され、それによりAFT引込み範囲の減少が阻
止されて誤動作が防止される。また、微弱電界強度時は
AFT制御電圧がAFT動作停止時の一定値に固定されること
により誤動作が防止される。(E) Operation According to the above configuration, the weak electric field strength corrects the decrease in the AFT control voltage, thereby preventing the decrease in the AFT pull-in range and preventing malfunction. When the weak electric field strength is
Malfunction is prevented by fixing the AFT control voltage to a fixed value when AFT operation is stopped.
（ヘ） 実施例 第１図は本考案によるAFT回路の一実施例の要部を示
しており、この回路は大別するとAFT検波部（１）と、A
FT制御電圧出力部（２）と、受信電界強度検出部（３）
と、AFT制御電圧切換部（４）とから構成されている。(F) Embodiment FIG. 1 shows a main part of an embodiment of an AFT circuit according to the present invention. This circuit is roughly classified into an AFT detection part (1) and an AFT detection part (A).
FT control voltage output section (2) and received electric field strength detection section (3)
And an AFT control voltage switching unit (4).
前記AFT検波部（１）は、差動信号型式のVIF信号が導
入される一対の入力端子（Ｉ1）と、90°移相回路
（５）と、二重平衡差動型復調回路（６）とからなる周
知のクォドラチャ検波型に構成されており、その定電流
源トランジスタ（Ｔ7）のベースに検波動作オン・オフ
用のスイッチングトランジスタ（Ｔ8）が接続されてい
る。The AFT detector (1) includes a pair of input terminals (I 1 ) into which a VIF signal of a differential signal type is introduced, a 90 ° phase shift circuit (5), and a double balanced differential demodulator circuit (6). ) And a well-known quadrature detection type, and a switching transistor (T 8 ) for on / off detection operation is connected to the base of the constant current source transistor (T 7 ).
次に前記AFT制御電圧出力部（２）は、上記差動型復
調回路（６）の出力電流路に対して図示の如く接続され
た第１〜第３電流ミラー回路（７）（８）（９）と、そ
の第２第３電流ミラー回路（８）（９）の出力電流に応
じて充放電されるAFT制御電圧取り出し用のコンデンサ
（Ｃ1）と、出力抵抗（Ｒ1）（Ｒ2）からなる周知の構
成である。Next, the AFT control voltage output section (2) is connected to the output current path of the differential demodulation circuit (6) as shown in the drawing, and the first to third current mirror circuits (7) (8) ( 9), a capacitor (C 1 ) for extracting the AFT control voltage charged and discharged according to the output currents of the second and third current mirror circuits (8) and (9), and an output resistance (R 1 ) (R 2 ) Is a well-known configuration.
一方、前記電界強度検出部（３）は、図示しないAGC
検波回路からのIF・AGC電圧が端子（Ｉ2）及び抵抗（Ｒ
3）（Ｒ4）をそれぞれ介して各一方のベースに入力され
各他方のベースに抵抗（Ｒ5）（Ｒ6）（Ｒ7）による一
定電圧（Vr1）（Vr2）がそれぞれ印加される第１第２差
動比較回路（10）（11）からなる。そして、その第１差
動比較回路（10）のトランジスタ（Ｔ19）の出力電力
が、前記AFT検波部（１）の検波動作オン・オフ用のト
ランジスタ（Ｔ8）のベースに抵抗（Ｒ8）を介して印加
されるようになっている。On the other hand, the electric field strength detector (3) is
The IF / AGC voltage from the detector circuit is applied to the terminal (I 2 ) and the resistor (R
3 ) (R 4 ) is applied to each of the bases and a constant voltage (Vr 1 ) (Vr 2 ) is applied to each of the other bases by resistors (R 5 ) (R 6 ) (R 7 ). It is composed of first and second differential comparison circuits (10) and (11). Then, the output power of the transistor (T 19 ) of the first differential comparison circuit (10) causes the resistance (R 8 ) to be applied to the base of the transistor (T 8 ) for the detection operation ON / OFF of the AFT detection unit (1). ) Is applied via.
次に、前記AFT制御電圧切換部（４）は、上記第２差
動比較回路（11）のトランジスタ（Ｔ22）の出力電圧が
それぞれ抵抗（Ｒ9）（Ｒ10）及び（Ｒ11）（Ｒ12）を
介して入力されるスイッチングトランジスタ（Ｔ24）
（Ｔ25）と、その各トランジスタに応答してオン・オフ
するFET（Ｔ26）（Ｔ27）と、出力抵抗（Ｒ13）
（Ｔ14）等からなり、そのFET（Ｔ26）（Ｔ27）の接続
中点がAFT制御電圧出力点（Ａ）に接続されている。Then, the AFT control voltage switching unit (4), said output voltage resistors of the transistors of the second differential comparator circuit (11) (T 22) ( R 9) (R 10) and (R 11) ( Switching transistor (T 24 ) input via R 12 )
(T 25 ), FETs (T 26 ) (T 27 ) that are turned on / off in response to the respective transistors, and an output resistance (R 13 ).
(T 14 ) etc., and the connection middle point of the FETs (T 26 ) (T 27 ) is connected to the AFT control voltage output point (A).
したがって、今、この実施例に於いて、前述のIF・AG
C電圧がテレビジョン信号の受信電界強度の低下につれ
て増大するものとすると、先ず、中電界強度以上の状態
では次のようになる。即ち、このときは、受信電界強度
検出部（３）の第１差動比較回路（10）のトランジスタ
（Ｔ18）がオフでトランジスタ（Ｔ19）がオンとなって
いるので、検波動作オン・オフ用のトランジスタ
（Ｔ8）はオフであって、AFT検波が何等影響を受けるこ
となく行なわれる。また、このとき、第２差動比較回路
（11）のトランジスタ（Ｔ21）がオフでトランジスタ
（Ｔ22）がオンであるから、AFT制御電圧切換部（４）
のトランジスタ（Ｔ24）（Ｔ25）がオフとなってFET
（Ｔ26）（Ｔ27）がオンになり、AFT制御電圧出力点
（Ａ）に出力抵抗（Ｒ13）（Ｒ14）が接続されているこ
とになる。Therefore, in this embodiment, the IF / AG
Assuming that the C voltage increases as the reception electric field strength of the television signal decreases, the following is first obtained when the electric field strength is medium or higher. That is, at this time, since the transistor (T 18 ) of the first differential comparison circuit (10) of the reception electric field strength detection unit (3) is off and the transistor (T 19 ) is on, the detection operation is turned on. The transistor (T 8 ) for turning off is off, and the AFT detection is performed without any influence. At this time, since the transistor (T 21 ) of the second differential comparison circuit (11) is off and the transistor (T 22 ) is on, the AFT control voltage switching unit (4)
Transistor (T 24 ) (T 25 ) is turned off and FET
(T 26 ) and (T 27 ) are turned on, and the output resistors (R 13 ) and (R 14 ) are connected to the AFT control voltage output point (A).
次に、電界強度が低下して弱電界強度状態になると、
IF・AGC電圧が上昇して第２差動比較回路（11）のトラ
ンジスタ（Ｔ22）がオフとなるが、第１差動比較回路
（10）のトランジスタ（Ｔ19）は依然としてオンである
状態になる。すると、このときはAFT検波部（１）は依
然として検波動作するが、切換部（４）のFET（Ｔ26）
（Ｔ27）が何れもオフになるから、AFT制御電圧出力点
（Ａ）には出力抵抗（Ｒ1）（Ｒ2）のみ接続されること
になって、出力インピーダンスが増大する。このため、
電界強度の低下によるAFT制御電圧の振幅減少が補正さ
れることになり、AFT制御電圧特性は第２図の実線（中
電界強度以上）から破線のようになる。Next, when the electric field strength is reduced to a weak electric field strength state,
The IF (AGC) voltage rises and the transistor (T 22 ) of the second differential comparison circuit (11) is turned off, but the transistor (T 19 ) of the first differential comparison circuit (10) is still on. become. Then, at this time, the AFT detection unit (1) still performs the detection operation, but the FET (T 26 ) of the switching unit (4)
Since both (T 27 ) are turned off, only the output resistors (R 1 ) and (R 2 ) are connected to the AFT control voltage output point (A), and the output impedance increases. For this reason,
The decrease in the amplitude of the AFT control voltage due to the decrease in the electric field strength is corrected, and the AFT control voltage characteristic changes from the solid line (above the middle electric field strength) to the broken line in FIG.
更に、電界強度が一段と低下して微弱電界強度状態に
なると、第１差動比較回路（10）のトランジスタ
（Ｔ18）もオンになり、トランジスタ（Ｔ19）がオフに
なる。このため、検波動作オン・オフ用のトランジスタ
（Ｔ8）がオンとなって定電流源トランジスタ（Ｔ7）を
オフにするから、AFT検波部（１）は動作を停止し、そ
の各トランジスタに電流が流れない。従って、AFT制御
電圧出力部（２）の各トランジスタにも電流が流れず、
その結果、Ａ点のAFT制御電圧は、第２図の一点鎖線の
如く、電源電圧（＋Vcc）と出力抵抗（Ｒ1）（Ｒ2）の
分圧比で決まる一定値に保持される。Furthermore, when the electric field strength further decreases and becomes a weak electric field strength state, the transistor (T 18 ) of the first differential comparison circuit (10) also turns on and the transistor (T 19 ) turns off. Therefore, the detection operation on / off transistor (T 8 ) is turned on and the constant current source transistor (T 7 ) is turned off, so that the AFT detection unit (1) stops its operation and No current flows. Therefore, no current flows through each transistor of the AFT control voltage output section (2),
As a result, the AFT control voltage at the point A is held at a constant value determined by the voltage division ratio between the power supply voltage (+ Vcc) and the output resistances (R 1 ) (R 2 ) as shown by the chain line in FIG.
（ト） 考案の効果 以上の如く本考案のAFT回路に依れば、AFT制御電圧特
性を電界強度に応じて数段階に切換えるようにしている
ので、弱電界受信時だけでなく、それよりも更に電界強
度の低い微弱電界受信時に於いても、不所望な周波数に
限ってロックされる等の誤動作を防止できる。(G) Effect of the device As described above, according to the AFT circuit of the present invention, the AFT control voltage characteristic is switched in several stages according to the electric field strength. Further, even when a weak electric field having a low electric field strength is received, it is possible to prevent malfunction such as locking only at an undesired frequency.
第１図は本考案のAFT回路の一実施例を示す回路図、第
２図はそのAFT制御電圧特性を示す特性図、第３図及び
第４図は何れも従来のAFT回路の欠点を説明するための
特性図である。 （１）:AFT検波部、（２）:AFT制御電圧出力部、
（３）：受信電界強度検出部、（４）:AFT制御電圧切換
部、（Ｔ8）：検波動作オン・オフ用のスイッチングト
ランジスタ。FIG. 1 is a circuit diagram showing one embodiment of the AFT circuit of the present invention, FIG. 2 is a characteristic diagram showing its AFT control voltage characteristic, and FIGS. 3 and 4 are all for explaining the defects of the conventional AFT circuit. It is a characteristic diagram for doing. (1): AFT detection section, (2): AFT control voltage output section,
(3): received signal strength detecting unit, (4): AFT control voltage switching section, (T 8): a switching transistor for detecting operation on and off.
Claims (2)
る電界検出手段と、その検出出力に応じてAFT制御電圧
特性を切換制御する切換制御手段とからなり、弱電界強
度時にAFT制御電圧が増大するよう切換えることを特徴
としたテレビジョン受像機のAFT回路。1. An electric field detecting means for detecting a received electric field strength of a television signal, and a switching control means for switching and controlling an AFT control voltage characteristic according to the detected output, wherein the AFT control voltage increases when the electric field strength is weak. AFT circuit of a television receiver characterized by switching to
止時の一定値に切換えられるようにした請求項１記載の
テレビジョン受像機のAFT回路。2. The AFT circuit of a television receiver according to claim 1, wherein the AFT control voltage is switched to a constant value when the AFT operation is stopped when the electric field strength is weak.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1988138924U JPH084753Y2 (en) | 1988-10-25 | 1988-10-25 | AFT circuit of television receiver |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1988138924U JPH084753Y2 (en) | 1988-10-25 | 1988-10-25 | AFT circuit of television receiver |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0260343U JPH0260343U (en) | 1990-05-02 |
| JPH084753Y2 true JPH084753Y2 (en) | 1996-02-07 |
Family
ID=31401708
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP1988138924U Expired - Lifetime JPH084753Y2 (en) | 1988-10-25 | 1988-10-25 | AFT circuit of television receiver |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH084753Y2 (en) |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5794276U (en) * | 1980-11-28 | 1982-06-10 | ||
| JPS60101871U (en) * | 1983-12-19 | 1985-07-11 | 株式会社東芝 | television receiver |
| JPS6257479U (en) * | 1985-09-26 | 1987-04-09 |
-
1988
- 1988-10-25 JP JP1988138924U patent/JPH084753Y2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0260343U (en) | 1990-05-02 |
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