JPH03158010A - Optical demodulation circuit - Google Patents
Optical demodulation circuitInfo
- Publication number
- JPH03158010A JPH03158010A JP29611889A JP29611889A JPH03158010A JP H03158010 A JPH03158010 A JP H03158010A JP 29611889 A JP29611889 A JP 29611889A JP 29611889 A JP29611889 A JP 29611889A JP H03158010 A JPH03158010 A JP H03158010A
- Authority
- JP
- Japan
- Prior art keywords
- preamplifier
- negative feedback
- changeover switch
- gain control
- 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.)
- Pending
Links
- 230000003287 optical effect Effects 0.000 title claims description 16
- 230000003321 amplification Effects 0.000 abstract description 2
- 238000003199 nucleic acid amplification method Methods 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
Abstract
Description
【発明の詳細な説明】
（産業上の利用分野）
本発明は、映像信号で直接光強度変調された光信号を復
調する自動利得制御回路付光復調回路に関するものであ
る。DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical demodulation circuit with an automatic gain control circuit that demodulates an optical signal that has been directly modulated in optical intensity with a video signal.
（従来の技術）
第２図は従来例を示す、Ｂは電源端子、ＯＵＴは映像信
号の出力端子である。映像信号で光強度変調された光は
、受光素子Ｄ１で微弱な電気信号に変換され、前置増幅
器Ａ４．自動利得制御増幅器Ａ５を経て、元の信号に復
調される。ＦＢｌ。(Prior Art) FIG. 2 shows a conventional example, where B is a power supply terminal and OUT is an output terminal for a video signal. The light intensity modulated by the video signal is converted into a weak electrical signal by the light receiving element D1, and then sent to the preamplifier A4. The signal is demodulated to the original signal via an automatic gain control amplifier A5. FBl.
ＦＢ２は負帰還回路で、自動利得制御増幅器Ａ５に制御
範囲を超える過大入力がある場合には、負帰還定数が大
きくなるように負帰還切り換えスイッチＳＷＩを操作し
、自動利得制御増幅器Ａ５への入力レベルを下げ、正常
に動作させる。FB2 is a negative feedback circuit, and when there is an excessive input that exceeds the control range to the automatic gain control amplifier A5, the negative feedback changeover switch SWI is operated so that the negative feedback constant becomes large, and the input to the automatic gain control amplifier A5 is changed. Lower the level and make it work normally.
また、光信号が弱い場合には、負帰還定数が小さくなる
ように負帰還切り換えスイッチＳＷ２を操作して自動利
得制御増幅器Ａ５への入力レベルを上げる。負帰還切り
換えスイッチＳＷＩとＳＷ２の操作により利得制御範囲
をほぼ２倍にしている。Furthermore, when the optical signal is weak, the negative feedback changeover switch SW2 is operated to increase the input level to the automatic gain control amplifier A5 so that the negative feedback constant becomes small. The gain control range is approximately doubled by operating the negative feedback changeover switches SWI and SW2.
（発明が解決しようとする課１１）
しかし、上記負帰還切り換えスイッチＳＷ２の操作で負
帰還回路を選択する時、映像信号の周波数特性が影響を
受ける欠点があり、特に光信号が弱い時、負帰還切り換
えスイッチＳＷ２で負帰環定数を小さくすると周波数特
性が劣化した。(Problem 11 to be solved by the invention) However, when selecting the negative feedback circuit by operating the negative feedback changeover switch SW2, there is a drawback that the frequency characteristics of the video signal are affected, and especially when the optical signal is weak, the negative When the negative feedback constant was decreased using the feedback changeover switch SW2, the frequency characteristics deteriorated.
本発明は、上記の問題を解決するために、自動利得制御
増幅器の入力が過大にならない光復調回路を提供するこ
とを目的とする。SUMMARY OF THE INVENTION In order to solve the above problems, it is an object of the present invention to provide an optical demodulation circuit in which the input of an automatic gain control amplifier does not become excessive.
（課題を解決するための手段）
前記目的を達成するために、本発明の光復調回路は、負
帰還定数を一定にした負帰還回路を備えたｆ５１前置増
幅器と、第１前置増幅器の後段に設けられた第２前置増
幅器と、第２前置増幅器の有無を選択できる切り換えス
イッチと、当該切り換えスイッチにより適性レベルに増
幅された入力信号を増幅する自動利得制御増幅器とから
構成される。(Means for Solving the Problems) In order to achieve the above object, the optical demodulation circuit of the present invention includes an f51 preamplifier equipped with a negative feedback circuit with a constant negative feedback constant, and a first preamplifier. Consisting of a second preamplifier provided at the rear stage, a changeover switch that can select whether or not the second preamplifier is included, and an automatic gain control amplifier that amplifies the input signal amplified to an appropriate level by the changeover switch. .
（作 用）
本発明の第１段目の前置増幅器は、負帰還定数を一定に
して負帰還をかけている。弱い光信号を受信した時のた
めに、第２段目には負帰還なしの前置増幅器が設けられ
ている。そして、切り換えスイッチにより、強い光信号
の場合には、第１段の前置増幅器の増幅だけで自動利得
制御増幅器に入力され、弱い光信号の場合には、第１前
置増幅器と第２前置増幅器とで増幅されてから自動利得
制御増幅器に入力される。(Function) The first stage preamplifier of the present invention applies negative feedback by keeping the negative feedback constant constant. In case a weak optical signal is received, the second stage is provided with a preamplifier without negative feedback. Then, by means of a changeover switch, in the case of a strong optical signal, the amplification of only the first preamplifier is input to the automatic gain control amplifier, and in the case of a weak optical signal, the first preamplifier and the second preamplifier are input to the automatic gain control amplifier. The signal is amplified by a stationary amplifier and then input to an automatic gain control amplifier.
したがって、自動利得制御増幅器の入力は、過大になる
ことはない。Therefore, the input of the automatic gain control amplifier will not become too large.
（実施例）
第１図に本発明における一実施例を示す、第１図におい
て、Ｄｌ及びＡ３は第２図に示した受光素子及び自動利
得制御増幅器で、Ａ１は第２図に示したＡ４に相当する
前置増幅器で、負帰還回路ＦＢ３が接続されている０弱
い光を受光する場合は、前置増幅器Ａ１の出力はさらに
第２の前置増幅器Ａ２に入り増幅されて、負帰還切り換
えスイッチＳＷ２のａ接点からＣＯＭ、端子を経て自動
利得制御増幅器Ａ３に入る０強い光を受光する場合は、
負帰還切り換えスイッチＳＷ２を切り換ええて、前置増
幅器Ａ１の出力は、負帰還切り換えスイッチＳＷ２のｂ
接点から００Ｍ端子を経て自動利得制御増幅器Ａ３に直
接、増幅されることなく入り過大入力とならないように
する。このとき負帰還切り換えスイッチＳＷ２と連動し
て動く負帰還切り換えスイッチＳＷ３の接点を開放し、
前置増幅器Ａ２の電源を切る。即ち前置増幅器Ａ２の電
源供給用トランジスタＴＲのベース抵抗Ｒ２に流れる電
流を阻止し電源Ｂを切る。なお、Ｒ１はバイアス抵抗で
ある。(Embodiment) Fig. 1 shows an embodiment of the present invention. In Fig. 1, Dl and A3 are the light receiving element and automatic gain control amplifier shown in Fig. 2, and A1 is A4 shown in Fig. 2. A preamplifier corresponding to 0 is connected to a negative feedback circuit FB3. When receiving weak light, the output of the preamplifier A1 is further input to a second preamplifier A2, where it is amplified and negative feedback switching is performed. When receiving strong light that enters the automatic gain control amplifier A3 from the a contact of the switch SW2 through the COM terminal and the terminal,
By switching the negative feedback changeover switch SW2, the output of the preamplifier A1 is changed to the negative feedback changeover switch SW2.
The signal directly enters the automatic gain control amplifier A3 from the contact via the 00M terminal without being amplified, thereby preventing an excessive input. At this time, the contact of the negative feedback changeover switch SW3, which operates in conjunction with the negative feedback changeover switch SW2, is opened,
Turn off preamplifier A2. That is, the current flowing through the base resistor R2 of the power supply transistor TR of the preamplifier A2 is blocked, and the power supply B is turned off. Note that R1 is a bias resistance.
（発明の効果）
実施例に示すように、本発明によれば、負帰還回路にお
ける負帰還量をスイッチの切り換えにより行わずに後段
の前置増幅、器を切り換えて過大入力対策としたので、
負帰還回路の切り換えに伴なう映像信号の周波数特性の
変動をなくすようにできる。また、負帰還回路は、イン
ピーダンスが高く、切り換えスイッチの浮遊量の影響も
受けやすく、特に、微小回路電流のため切り換えスイッ
チを遠くへ設置することは途中で誘起する電流の影響が
無視できず、不可能であった。しかし、本発明によれば
、前置増幅器を切り換えるスイッチは、回路電流が大き
く、インピーダンスも比較的低く、遠くへ設置しても大
きい影響を受けない、増幅器を切り換えるスイッチを遠
くへ設置できることは。(Effects of the Invention) As shown in the embodiments, according to the present invention, the amount of negative feedback in the negative feedback circuit is not changed by changing the switch, but the preamplifier in the subsequent stage is changed to prevent excessive input.
It is possible to eliminate fluctuations in the frequency characteristics of the video signal due to switching of the negative feedback circuit. In addition, the negative feedback circuit has high impedance and is easily affected by the stray amount of the changeover switch.In particular, if the changeover switch is installed far away due to the small circuit current, the influence of the current induced along the way cannot be ignored. It was impossible. However, according to the present invention, the switch for switching the preamplifier has a large circuit current, has a relatively low impedance, and can be installed far away without being affected greatly.
この光復調器を組む装置の大きさ、スイッチ操作面等の
制約がある時に装置設計を容易にすることができる。When there are restrictions on the size of the device in which the optical demodulator is assembled, the switch operation surface, etc., the device design can be facilitated.
第１図は本発明の一実施例を示す図、第２図は従来例を
示す図である。
Ｄｉ ・・・受光素子、 Ａｌ、Ａ２．Ａ４・・・前置
増幅器、Ａ３ ・・・自動利得制御増幅器。FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional example. Di...light receiving element, Al, A2. A4...Preamplifier, A3...Automatic gain control amplifier.
Claims (1)
利得制御回路付光復調回路において、負帰還定数を一定
にした負帰還回路を備えた第１前置増幅器と、 第１前置増幅器の後段に設けられた第２前置増幅器と、 第２前置増幅器の有無を選択できる切り換えスイッチと
、 当該切り換えスイッチにより適性レベルに増幅された入
力信号を増幅する自動利得制御増幅器と、を備えたこと
を特徴とする光復調回路。[Scope of claims] An optical demodulation circuit with an automatic gain control circuit that demodulates an optical signal directly modulated in optical intensity with a video signal, comprising: a first preamplifier including a negative feedback circuit with a constant negative feedback constant; A second preamplifier provided after the first preamplifier, a changeover switch that can select whether or not to include the second preamplifier, and automatic gain control that amplifies the input signal amplified to an appropriate level by the changeover switch. An optical demodulation circuit comprising an amplifier.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29611889A JPH03158010A (en) | 1989-11-16 | 1989-11-16 | Optical demodulation circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29611889A JPH03158010A (en) | 1989-11-16 | 1989-11-16 | Optical demodulation circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH03158010A true JPH03158010A (en) | 1991-07-08 |
Family
ID=17829369
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP29611889A Pending JPH03158010A (en) | 1989-11-16 | 1989-11-16 | Optical demodulation circuit |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH03158010A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006270969A (en) * | 2005-03-24 | 2006-10-05 | Avago Technologies General Ip (Singapore) Private Ltd | Automatic gain control circuit for infrared receiver |
-
1989
- 1989-11-16 JP JP29611889A patent/JPH03158010A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006270969A (en) * | 2005-03-24 | 2006-10-05 | Avago Technologies General Ip (Singapore) Private Ltd | Automatic gain control circuit for infrared receiver |
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