JPH05335882A - Active filter - Google Patents

Active filter

Info

Publication number
JPH05335882A
JPH05335882A JP13691992A JP13691992A JPH05335882A JP H05335882 A JPH05335882 A JP H05335882A JP 13691992 A JP13691992 A JP 13691992A JP 13691992 A JP13691992 A JP 13691992A JP H05335882 A JPH05335882 A JP H05335882A
Authority
JP
Japan
Prior art keywords
resistor
input terminal
buffer
negative feedback
feedback amplifier
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
Application number
JP13691992A
Other languages
Japanese (ja)
Inventor
Takao Mamada
隆男 間々田
Nobuyuki Otaka
信行 大高
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sanyo Electric Co Ltd
Original Assignee
Sanyo Electric Co Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Sanyo Electric Co Ltd filed Critical Sanyo Electric Co Ltd
Priority to JP13691992A priority Critical patent/JPH05335882A/en
Publication of JPH05335882A publication Critical patent/JPH05335882A/en
Pending legal-status Critical Current

Links

Abstract

PURPOSE:To reduce noise by forming the active filter with a 2nd capacitor connected between a connecting point of a 1st resistor and an input terminal of a buffer and an output terminal of a negative feedback amplifier and obtaining an output signal from the output terminal of the negative feedback amplifier. CONSTITUTION:An input of a buffer 10 connects to a 1st resistor 2RA and its output connects to a 2nd resistor 3RB. An input signal from an input terminal 1 and a feedback signal from a 2nd capacitor 6 pass through the buffer 10 without any modification and the passed signal is fed to a resistor 3. On the other hand, an impedance when viewing the input terminal 1 from a noninverting input terminal (+) of a negative feedback amplifier 5 is only RB in the equivalent circuit and a resistance RA is reduced. Thus, noise generated by the filter itself is reduced. Since the provision of the buffer 10 is enough, it is not required to increase number of components.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【産業上の利用分野】本発明は、ＩＣに内蔵されるアク
ティブフィルタに関するもので、特に該フィルタ自身か
ら発生するノイズの低減を図ったアクティブフィルタに
関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active filter incorporated in an IC, and more particularly to an active filter designed to reduce noise generated by the filter itself.

【０００２】[0002]

【従来の技術】ＩＣに内蔵される二次のアクティブロー
パスフィルタとして図２の如きアクティブフィルタが知
られている。入力端子（１）からの入力信号は、第１抵
抗（２）、第２抵抗（３）及び第１コンデンサ（４）を
介して負帰還増幅器（５）に印加される。負帰還増幅器
（５）の出力信号は、第２コンデンサ（６）を介して点
Ａに帰還される。その結果、出力端子（７）にローパス
フィルタ出力が得られる。2. Description of the Related Art An active filter as shown in FIG. 2 is known as a secondary active low-pass filter incorporated in an IC. The input signal from the input terminal (1) is applied to the negative feedback amplifier (5) via the first resistor (2), the second resistor (3) and the first capacitor (4). The output signal of the negative feedback amplifier (5) is fed back to the point A via the second capacitor (6). As a result, a low-pass filter output is obtained at the output terminal (7).

【０００３】[0003]

【発明が解決しようとする課題】ところで、負帰還増幅
器では増幅器内部から発生するノイズ（雑音）を有して
おり、それが出力に発生してしまう。図３は、ノイズ発
生の説明に供するための負帰還増幅器を示すものであ
る。図３の出力端子（８）に発生するノイズをＶn0とす
ると、該Ｖn0は、By the way, the negative feedback amplifier has a noise generated from the inside of the amplifier, which is generated at the output. FIG. 3 shows a negative feedback amplifier for explaining the noise generation. If the noise generated at the output terminal (8) in FIG. 3 is Vn 0 , the Vn 0 is

【０００４】[0004]

【数１】 [Equation 1]

【０００５】 と表わされる。式（１）において、ノイズ電圧Ｖn及び
ノイズ電流Ｉn1，Ｉn2は、増幅器固有の値であるため低
減させることは出来ない。そこで、式（１）の抵抗値Ｒ
1，ＲG及びＲFを低下させることにより、ノイズＶn0を
低減させることが考えられる。図２の回路では、負帰還
増幅器（５）の負入力端子（−）に負荷が接続されてい
ないので、正入力端子（＋）についてのみ考える。前記
正入力端子（＋）から、入力端子（１）側を見たときの
インピーダンスは、図５の如く表わされる。今、入力信
号の周波数が低く（オーディオ帯域）、第１及び第２コ
ンデンサ（４）及び（６）の容量値ＣA及びＣBが大きい
とすれば、図５の前記容量値ＣA及びＣBは無視できる。
そのため、図５の端子（９）から見えるインピーダンス
は、（ＲA＋ＲB）となる。[0005] Is expressed as In the equation (1), the noise voltage Vn and the noise currents In 1 and In 2 are values unique to the amplifier and cannot be reduced. Therefore, the resistance value R of the equation (1)
It is possible to reduce the noise Vn 0 by reducing 1 , R G and R F. In the circuit of FIG. 2, since the load is not connected to the negative input terminal (−) of the negative feedback amplifier (5), only the positive input terminal (+) will be considered. The impedance when the input terminal (1) side is viewed from the positive input terminal (+) is represented as shown in FIG. Now, assuming that the frequency of the input signal is low (audio band) and the capacitance values C A and C B of the first and second capacitors (4) and (6) are large, the capacitance values C A and C of FIG. B can be ignored.
Therefore, the impedance seen from the terminal of FIG. 5 (9) becomes (R A + R B).

【０００６】ところで、図２の回路をＩＣ化する場合、
チップ面積の削減を図かるため、容量値ＣA及びＣBは出
来るだけ小さくし、抵抗値ＲA及びＲBを大きくする。そ
の為、前記インピーダンス（ＲA＋ＲB）の値は、必然的
に大きくなってしまい、前述のノイズ低減という目的に
悪影響を及ぼす、という問題があった。By the way, when the circuit of FIG. 2 is integrated into an IC,
In order to reduce the chip area, the capacitance values C A and C B are made as small as possible and the resistance values R A and R B are made large. Therefore, there is a problem that the value of the impedance (R A + R B ) inevitably becomes large, which adversely affects the above-mentioned object of noise reduction.

【０００７】[0007]

【課題を解決するための手段】本発明は上述の点に鑑み
成されたもので、入力端子からの入力信号が一端に印加
される第１抵抗と、入力端子が前記第１抵抗の他端に接
続され、出力端子が第２抵抗の一端に接続されたバッフ
ァと、前記第２抵抗の他端に接続された第１コンデンサ
と、入力端子が前記第２抵抗の他端に接続された負帰還
増幅器と、前記第１抵抗と前記バッファの入力端子との
接続点と前記負帰還増幅器の出力端子との間に接続され
た第２コンデンサとから成り、前記負帰還増幅器の出力
端子より出力信号を得るようにしたことを特徴とする。SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a first resistor to which an input signal from an input terminal is applied to one end, and the other end of the first resistor having the input terminal. A buffer having an output terminal connected to one end of a second resistor, a first capacitor connected to the other end of the second resistor, and an input terminal connected to a negative end of the second resistor. An output signal from the output terminal of the negative feedback amplifier; and a second capacitor connected between the connection point of the first resistor and the input terminal of the buffer and the output terminal of the negative feedback amplifier. Is characterized in that

【０００８】[0008]

【作用】本発明に依れば、第１及び第２抵抗の間に、バ
ッファを設けているので、負帰還増幅器の入力端子から
入力端子を見たインピーダンスを第２抵抗のみに限定す
ることができ、ノイズ低減が可能となる。According to the present invention, since the buffer is provided between the first and second resistors, the impedance seen from the input terminal of the negative feedback amplifier to the input terminal can be limited to only the second resistor. Therefore, noise can be reduced.

【０００９】[0009]

【実施例】図１は、本発明の一実施例を示す回路図で、
（１０）は入力が第１抵抗（２）ＲAに、出力が第２抵
抗（３）ＲBに接続されたバッファである。尚、図１に
おいて、図２と同一の回路素子については同一の符号を
付し、説明を省略する。DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an embodiment of the present invention.
(10) is a buffer whose input is connected to the first resistor (2) R A and whose output is connected to the second resistor (3) R B. In FIG. 1, the same circuit elements as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

【００１０】図２において、入力端子（１）からの入力
信号及び第２コンデンサ（６）からの帰還信号は、バッ
ファ（１０）をそのまま通過して第２抵抗（３）に印加
されるので、図２の本来のフィルタ特性に関しては何ら
影響を及ぼさない。一方、負帰還増幅器（５）の正入力
端子（＋）から入力端子（１）側を見たインピーダンス
の等価回路は、図４の如く表わされる。この場合のイン
ピーダンスは、ＲBのみとなり、図５の場合に比べて抵
抗値ＲAをそのまま削減できる。In FIG. 2, the input signal from the input terminal (1) and the feedback signal from the second capacitor (6) pass through the buffer (10) as they are and are applied to the second resistor (3). It has no effect on the original filter characteristics of FIG. On the other hand, an equivalent circuit of the impedance when the input terminal (1) side is viewed from the positive input terminal (+) of the negative feedback amplifier (5) is shown in FIG. In this case, the impedance is only R B, and the resistance value R A can be reduced as compared with the case of FIG.

【００１１】従って、図１の回路に依ればフィルタ自身
から発生するノイズを低減できる。Therefore, the circuit of FIG. 1 can reduce the noise generated from the filter itself.

【００１２】[0012]

【発明の効果】以上述べた如く、本発明に依ればＩＣに
内蔵されるアクティブフィルタ自身から発生するノイズ
を低減することができる。又、本発明に依れば、バッフ
ァを設けるだけで良いので、素子数の増加も招かないと
いう利点を有する。As described above, according to the present invention, noise generated from the active filter itself incorporated in the IC can be reduced. Further, according to the present invention, since it is only necessary to provide a buffer, there is an advantage that the number of elements does not increase.

【図面の簡単な説明】[Brief description of drawings]

【図１】本発明のアクティブフィルタを示す回路図であ
る。FIG. 1 is a circuit diagram showing an active filter of the present invention.

【図２】従来のアクティブフィルタを示す回路図であ
る。FIG. 2 is a circuit diagram showing a conventional active filter.

【図３】ノイズ発生の原理説明に供する為の回路図であ
る。FIG. 3 is a circuit diagram for explaining the principle of noise generation.

【図４】図１の説明に供するための回路図である。FIG. 4 is a circuit diagram for explanation of FIG.

【図５】図２の説明に供するための回路図である。FIG. 5 is a circuit diagram for use in explaining FIG.

【符号の説明】[Explanation of symbols]

（２） 第１抵抗 （３） 第２抵抗 （４） 第１コンデンサ （５） 負帰還増幅器 （６） 第２コンデンサ （１０） バッファ (2) First resistor (3) Second resistor (4) First capacitor (5) Negative feedback amplifier (6) Second capacitor (10) Buffer

Claims (2)

【特許請求の範囲】[Claims] 【請求項１】 入力端子からの入力信号が一端に印加さ
れる第１抵抗と、 入力端子が前記第１抵抗の他端に接続され、出力端子が
第２抵抗の一端に接続されたバッファと、 前記第２抵抗の他端に接続された第１コンデンサと、 入力端子が前記第２抵抗の他端に接続された負帰還増幅
器と、 前記第１抵抗と前記バッファの入力端子との接続点と前
記負帰還増幅器の出力端子との間に接続された第２コン
デンサとから成り、前記負帰還増幅器の出力端子より出
力信号を得るようにしたことを特徴とするアクティブフ
ィルタ。1. A first resistor to which an input signal from an input terminal is applied to one end, and a buffer whose input terminal is connected to the other end of the first resistor and whose output terminal is connected to one end of the second resistor. A first capacitor connected to the other end of the second resistor, a negative feedback amplifier whose input terminal is connected to the other end of the second resistor, and a connection point between the first resistor and the input terminal of the buffer. And a second capacitor connected between the output terminal of the negative feedback amplifier and an output signal of the negative feedback amplifier. 【請求項２】 前記負帰還増幅器は、出力信号が直接負
入力端子に印加されることを特徴とする請求項１記載の
アクティブフィルタ。2. The active filter according to claim 1, wherein an output signal of the negative feedback amplifier is directly applied to a negative input terminal.
JP13691992A 1992-05-28 1992-05-28 Active filter Pending JPH05335882A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP13691992A JPH05335882A (en) 1992-05-28 1992-05-28 Active filter

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP13691992A JPH05335882A (en) 1992-05-28 1992-05-28 Active filter

Publications (1)

Publication Number Publication Date
JPH05335882A true JPH05335882A (en) 1993-12-17

Family

ID=15186645

Family Applications (1)

Application Number Title Priority Date Filing Date
JP13691992A Pending JPH05335882A (en) 1992-05-28 1992-05-28 Active filter

Country Status (1)

Country Link
JP (1) JPH05335882A (en)

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