JPS5842310A - Low frequency filter - Google Patents
Low frequency filterInfo
- Publication number
- JPS5842310A JPS5842310A JP13957481A JP13957481A JPS5842310A JP S5842310 A JPS5842310 A JP S5842310A JP 13957481 A JP13957481 A JP 13957481A JP 13957481 A JP13957481 A JP 13957481A JP S5842310 A JPS5842310 A JP S5842310A
- Authority
- JP
- Japan
- Prior art keywords
- resistor
- operational amplifier
- capacitor
- circuit
- filter
- 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
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H19/00—Networks using time-varying elements, e.g. N-path filters
- H03H19/004—Switched capacitor networks
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Networks Using Active Elements (AREA)
Abstract
Description
【発明の詳細な説明】
本発明は、モノリシ、りIC化に有利な構成にした低周
波アクティブフィルタに関する。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low frequency active filter having a structure that is advantageous for monolithic or IC implementation.
集積回路ではインダクタンスは作〕にくいので抵抗Rと
コンデンサc2用い、それにダイオード、トランジスタ
を組合せて所望回路を構成する。所望回路がフィルタで
あっても同様でこれを半導体集積回路化するKけC,R
およびトランジスタで構成する必要がある。ところでフ
ィルタの扱う周波数が低くなるとC,Hの値が大きくな
シ、小型化が困難忙なる。即ちコンデンサの容量を大に
するには誘電体の膜厚を減少し誘電率を増大させる方法
があるが、これらには限度があるから勢い電極面積を大
にする必要があル、大型化する。また抵抗値を大にする
釦は、断面積及び導電率の低減にはバラつき、安定性、
精度などの点で制約があるので、長さを大にする必要が
あり、やはシ大型化する。そこで従来は低周波帯フィル
タの半導体集積回路化は困難として、専らハイブリ、ド
方式が採用され、極端な小型化は断念されていた。Since it is difficult to create an inductance in an integrated circuit, a resistor R and a capacitor c2 are used, and a diode and a transistor are combined to form the desired circuit. Even if the desired circuit is a filter, the same applies to converting it into a semiconductor integrated circuit.
and transistors. However, as the frequency handled by the filter becomes lower, the values of C and H become larger, making it difficult and difficult to miniaturize the filter. In other words, there are methods to increase the capacitance of a capacitor by decreasing the thickness of the dielectric material and increasing the dielectric constant, but these methods have limitations, so it is necessary to increase the area of the electrodes, which increases the size. . In addition, the button that increases the resistance value has variations in cross-sectional area and conductivity reduction, stability,
Since there are restrictions in terms of accuracy, it is necessary to increase the length, which in turn increases the size. Conventionally, it was considered difficult to integrate low-frequency filters into semiconductor integrated circuits, and hybrid and de-type filters were used exclusively, giving up on extreme miniaturization.
モノリシ、りIC化に好適なフィルタとしてはスイ、チ
ド・キャパシタフィルタが゛ある。し・かしこのフィル
タは比較的大きなチオ1面積を必要とし、低コスト化が
阻害されているようである。ところでこのフィルタでは
スイッチドキャパシタを抵抗として機能させている。こ
のスイ、チドキャパシタ方弐忙よると高抵抗を精度よく
作ることができる。またIC化に適するフィルタとして
はBi −quad形フィルタがある。この型のフィル
タハ安定性に優れているが、可聴周波数帯の下限といら
た低周波帯では従来方式ではC,Rが大にな)過ぎる。Examples of filters suitable for use in monolithic or IC applications include Swiss and solid capacitor filters. However, this filter requires a relatively large area, which seems to hinder cost reduction. By the way, this filter uses a switched capacitor to function as a resistor. By using this type of capacitor, high resistance can be created with high precision. Further, as a filter suitable for IC implementation, there is a Bi-quad type filter. Although this type of filter has excellent stability, in the lower limit of the audible frequency range and in the low frequency band, the C and R values of the conventional method are too large.
そこで本発明は回路を工夫してC,Rがそれ程大でなく
ても済むようKL、かつスイ、チドキャパシタを利用し
て、IC化に適する小型化可能な低周波アクティブフィ
ルタを提供しようとするものである。次に図面を参照し
なから不発F!At詳細に説明する。Therefore, the present invention devises the circuit so that C and R do not need to be so large, and uses KL and switch/chip capacitors to provide a low-frequency active filter that can be made smaller and suitable for IC implementation. It is something. Next, don't refer to the drawings, F! At will be explained in detail.
第1図にB i −quad形バンドパスフィルタの回
路を示す。この回路はオペアンプOP1〜OP3、抵抗
R1−R11、コンデンサC1e C鵞を図示の如く接
続してなる。この回路の解析結果は「アクティブフィル
タの設計」(電子科学シリーズ52. pp 147)
などの文献に記載されているが、入力IN、 出力O
UT間の伝達関数の一般式T (S)はで表わさ−れ、
一方、@1図の回路で入力電圧Vt K対する出力電圧
Vs k求めてみると、となる。従って次式が成立する
。FIG. 1 shows a circuit of a B i -quad type bandpass filter. This circuit is formed by connecting operational amplifiers OP1 to OP3, resistors R1 to R11, and capacitors C1 to C1 as shown. The analysis result of this circuit is "Design of Active Filter" (Electronic Science Series 52. pp 147)
It is described in documents such as Input IN, Output O
The general formula T (S) of the transfer function between UTs is expressed as,
On the other hand, if we calculate the output voltage Vs k with respect to the input voltage Vt K using the circuit shown in Figure @1, we get the following. Therefore, the following equation holds.
こ\で一== R@ = Re 、肖= C,= C・
とすると、利得H1中心角周波数物、バンド幅Δ#は次
の如くなる。Ko\deichi == R@ = Re, Portrait = C, = C・
Then, the gain H1 center angular frequency product and the bandwidth Δ# are as follows.
I
H= −−−−・・−・(4)
A
上記(5)式からフィルタを低周波用従って物ヲ小にす
るK FiRe 、 C@’c大にする、及びまたはR
a /Rsを小にすればよいことが分る。Re k大に
するにはスイッチドキャパシタ構成とするのがよいが、
これfも限度はある。即ちスイ、チドキャパシタを高抵
抗にするKはそのキャパシタを小容量にするとよいが、
余り小容量にするのはストレイキャパシタがあるので不
可能である。Cot大にすることは、所要面積から制限
がある。この点、R4/R6を/j−にすることは甚だ
有効である。即ちRs/Rs ’fr小(1以下)Kす
れば−IC,は小さくてもよいことになり、小型化が可
能になる。R@/RiYr小にするK11jR*に小に
すればよく、これKは不純物濃度の高い拡散抵抗を使用
し、長さを短く従って小型化すればよい。またR・/R
sを小にするKはR,を大にすればよく、これにもスイ
、チドキャノ(シタの使用が好適である。なおRs、/
Rst小にすると前記の(6)式から明らかなようにQ
が下るが、これはRxt大にする等のことKより補正で
きる。I H= -----... (4) A From the above formula (5), make the filter for low frequencies, so make it smaller K FiRe, make C@'c larger, and or R
It turns out that a/Rs can be made small. In order to increase Re k, it is better to use a switched capacitor configuration, but
This f also has a limit. In other words, K, which makes a capacitor high in resistance, should have a small capacitance, but
It is impossible to make the capacitance too small because of the stray capacitor. There is a limit to increasing the size of Cot due to the required area. In this respect, it is extremely effective to set R4/R6 to /j-. That is, if Rs/Rs'fr is small (less than 1), -IC, can be small, and miniaturization becomes possible. It is sufficient to reduce R@/RiYr to K11jR*, and it is sufficient to use a diffused resistor with a high impurity concentration for K, and to shorten the length and thus reduce the size. Also R・/R
K, which reduces s, can be achieved by increasing R, and it is also suitable to use sui and chidokano (sita). Note that Rs, /
As is clear from equation (6) above, when Rst is made small, Q
decreases, but this can be corrected by increasing Rxt, etc.
第2図は拡散抵抗の抵抗値と所要面積の関係を示し、第
3図はスイ、チドキャパシタの抵抗値と所要面積の関係
を示す。これらのグラフから明らかなようにスイ、チド
キャパシタで抵抗R41構成してその抵抗値を大にし、
また拡散抵抗で抵抗R@を構成してその抵抗値を小にす
ると、いずれも小型化し、高密度集積回路化に好適であ
る。FIG. 2 shows the relationship between the resistance value of a diffused resistor and the required area, and FIG. 3 shows the relationship between the resistance value and the required area of a diode capacitor. As is clear from these graphs, by configuring the resistor R41 with a switch capacitor and increasing its resistance value,
Further, if the resistance value of the resistor R@ is made small by a diffused resistor, the size of the resistor R@ can be reduced, which is suitable for high-density integrated circuits.
第4図はスイッチドキャノ(シタの説明図である。FIG. 4 is an explanatory diagram of a switched canopy.
スイ、チドキャパシタについてはG、M# Jaeob
sstal : Design Tsehniq
uss for MOS 8vdteh*d
CapaeltorCodd@r Filt@rs
eなどに解説されているが、概略的には次の通シであ
る。即ちスイッチSを図面左側に倒してコンデンサCt
−入力端子v1で充電1次にスイッチSを図面右側に倒
して該コンデンサを出力側へ放電させ、次にスイッチs
2左側に倒してコンデンサc’2充電し、以下同様の操
作を繰り返す。コンデンサCの充電電荷QはQ=CV、
であり、これが出力側へ放電して電流を流すので、結局
入力INと出力OUTの間は抵抗で接続されているのと
等価になる。この等価抵抗t Req s スイッチ
の切換周波数t”faとすればRHQ = 1/fe−
Cである。スイッチSは実際には第4図(b) K示す
ようにトランジスタSt # s*で構成する。φ、¥
は互いに位相が180 異なる制御信号で、MOS )
ランジスタst l bRのゲートに加わってこれらを
互いに逆にオン、オフする。G, M# Jaeob for sui and chido capacitors
sstal: Design Tsehniq
uss for MOS 8vdteh*d
CapeltorCodd@r Filt@rs
Although it is explained in e.g., the general rule is as follows. That is, by flipping the switch S to the left side of the drawing, the capacitor Ct
- Charge first with input terminal v1, then turn switch S to the right side of the drawing to discharge the capacitor to the output side, then switch S
2 Turn to the left side to charge capacitor c'2, and repeat the same operation. The charge Q of the capacitor C is Q=CV,
Since this discharges to the output side and causes a current to flow, it becomes equivalent to connecting the input IN and the output OUT with a resistor. If this equivalent resistance t Req s is the switching frequency t”fa of the switch, then RHQ = 1/fe-
It is C. The switch S is actually composed of a transistor St#s* as shown in FIG. 4(b)K. φ、¥
are control signals with a phase difference of 180 degrees from each other (MOS)
It is added to the gates of transistors st l bR to turn them on and off in reverse order.
第5図は本発明の実施例を示す、第1図と比較すれば明
らかなようKこの回路もBi−quad形のバンドパス
フィルタ回路であ勺、礒抵抗Rs a RH# R,。FIG. 5 shows an embodiment of the present invention. As can be seen from a comparison with FIG. 1, this circuit is also a Bi-quad type band-pass filter circuit.
R4* R6vf−第4図(b)のスイ、チドキャパシ
タで置き換え、また抵抗鳥を拡散抵抗で構成しである。R4*R6vf--Switch and Tid capacitors in FIG. 4(b) are substituted, and the resistors are constructed with diffused resistors.
O印を付したコンデンサ・マークはスイ、チドキャパシ
タであることを示す。、演算増幅器OPt e OPH
の帰還路に挿入されるコンデンサC・はMOSキャパシ
タで構成する。このフィルタ回路はグラフィックイクオ
ーライザのバンドパスフィルタ部ニ使用するものとする
と、100 Hz〜10 KHzの周波数帯を複数個に
分割したその1つをノ(ンドノくスする必要がある。今
中心周波数100 Hzのパントノ(ス部を考えるには
一=2.5MΩとするなら、R,=−のとき(公知のB
i−quadフィルタではRi = Rsとするものが
多い)、C,=656pFとなる。2.5MΩのR。A capacitor mark with an O symbol indicates that it is a swiss capacitor or a swiss capacitor. , operational amplifier OPt e OPH
The capacitor C* inserted in the feedback path of is composed of a MOS capacitor. If this filter circuit is to be used in the bandpass filter section of a graphic equalizer, it is necessary to divide the frequency band from 100 Hz to 10 KHz into multiple parts and filter one of them. To consider the pantone noise part with a frequency of 100 Hz, if - = 2.5 MΩ, when R, = - (known B
In many i-quad filters, Ri = Rs), and C, = 656 pF. R of 2.5MΩ.
はスイ、チドキャパシタで容易に実現できるが、656
pFのC・はICとしては大き過ぎる。そこで本方式
によシーンR4= 0.1とすると、C・は6五6PF
でよいことKなり、小形化が可能になる。なおこのとき
R4/R,=0.01となるので、R4を拡散抵抗、R
s ’にスイ、チドキャパシタとし、前者i2.5にΩ
、後者1に250にΩとすれば上記の比a01が満足さ
れかつ両者とも大型化しないで済む。can be easily realized with a sui-do capacitor, but 656
C of pF is too large for an IC. Therefore, if we use this method and set scene R4 = 0.1, C. is 656PF
This makes it possible to downsize the device. At this time, R4/R, = 0.01, so R4 is the diffused resistance, R
s' is a capacitor, and the former i2.5 is Ω.
, the latter 1, 250 and Ω, the above ratio a01 is satisfied and both do not need to be increased in size.
以上説明したように本発明では安定性の優れたBi−q
uid形フィルタを用い、そのオペアンプ増幅段OPs
の利得を入力抵抗−と帰還抵抗−の比Rs/島によって
変えヤ所望中心周波数を得るに必要なRoC・の値を小
で済むようにしたので、また抵抗−を拡散抵抗、Ra5
hスイツチドキヤパシタにして大型化することなく前者
の低抵抗、後者の高抵抗化を図って上記比が得られるよ
うにしたので、小型化可能で、半導体集積回路化が容易
な低周波フィルタが得られる。As explained above, the present invention uses Bi-q with excellent stability.
Using a uid type filter, its operational amplifier amplification stage OPs
By changing the gain of the input resistor and the feedback resistor by changing the ratio Rs/I, the value of RoC required to obtain the desired center frequency can be kept small.
By making the former a low resistance and the latter a high resistance without increasing the size of the h-switched capacitor, the above ratio can be obtained, so the low frequency filter can be miniaturized and easily integrated into a semiconductor integrated circuit. is obtained.
第1図はB i −quad小形フィルタの回路図、第
2図及び第3図は抵抗値と所容面積との関係を示すグラ
フ、第4図はスイ、チドキャパシタの説明図、第5図は
本発明の実施例を示す回路図である。
図面で02里は第1の演算増幅器、OPlは第2の演算
増・嘔器、OPsは第3の演算増幅器である。
出願人 富士通テン株一式会社
代理人弁理士 青 柳 稔第2図
第3図
手続補正書(自発−)
昭和56年10月28 日
特許庁長官 島 1)春 樹 殿
1、事件の表示
昭和56年特許願第139574号
2発明の名称
低周波フィルタ
&補正をする者
事件との関係 特許出願人
住 所 兵庫県神戸市兵庫区御所通1丁目2番28号
名称 富士通テン株式会社
代表者 船 橋 章
4、代理人 〒101
&補正命令の日付 なし
&補正によシ増加する発明の数 なしl補正の対象
明細書の発明の詳細な説明の欄a補正の内容 (1)明
細書第5真下から2行の「されている力ζ」の次に「二
次帯域通過型の74 Aりの」を挿入する。
(2)同第5頁3行の記載を削除する。Figure 1 is a circuit diagram of the Bi-quad small filter, Figures 2 and 3 are graphs showing the relationship between resistance value and area, Figure 4 is an explanatory diagram of a sui-tido capacitor, and Figure 5 1 is a circuit diagram showing an embodiment of the present invention. In the drawing, 02 is a first operational amplifier, OP1 is a second operational amplifier, and OPs is a third operational amplifier. Applicant Fujitsu Ten Co., Ltd. Representative Patent Attorney Minoru Aoyagi Figure 2
Figure 3 Procedural amendment (voluntary) October 28, 1980 Director General of the Japan Patent Office Shima 1) Haruki Tono 1, Indication of the case 1982 Patent Application No. 139574 2 Name of the invention Low frequency filter & correction Relationship with the patent case Patent applicant address 1-2-28 Goshodori, Hyogo-ku, Kobe, Hyogo Prefecture Name Fujitsu Ten Ltd. Representative Funabashi Chapter 4, Agent Address 101 & Date of amendment order None & By amendment Number of inventions increasing None Subject to amendment
Contents of amendment in Column A of Detailed Description of the Invention in the Specification (1) Insert “Secondary band-pass type 74 A Rino” next to “Force ζ” in the second line from the bottom of No. 5 of the Specification. do. (2) Delete the statement on page 5, line 3.
Claims (1)
で構成される帰還回路を持つ@1の演算増幅器、人力抵
抗R,と、コンデンサCff1からなる#lR回路を持
つ第2の演算増幅器、および 入力抵抗−と、抵抗−からなる帰還回路を持つ第3の演
算増幅器を縦続接続し、かつ抵抗島によシ第3の演算増
幅器の出力端から第1の演算増幅器の入力端へ帰還を施
した回路を備え、前記の抵抗島をスイッチドキャパシタ
で構成し、抵抗R4は拡散抵抗で構成して、比Re/k
Yr 1よシ小としてなることを特徴とする低周波フ
ィルタ。[Claims] An operational amplifier @1 having an input resistor R4, a feedback circuit composed of a parallel circuit of a resistor 8 and a capacitor C1, a #lR circuit composed of a human resistor R, and a capacitor Cff1. A second operational amplifier and a third operational amplifier having a feedback circuit consisting of an input resistor and a resistor are connected in cascade, and a resistor island is used to connect the output terminal of the third operational amplifier to the first operational amplifier. It is equipped with a circuit that provides feedback to the input terminal, the resistor island is composed of a switched capacitor, the resistor R4 is composed of a diffused resistor, and the ratio Re/k is
A low frequency filter characterized in that Yr is smaller than 1.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP13957481A JPS5842310A (en) | 1981-09-04 | 1981-09-04 | Low frequency filter |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP13957481A JPS5842310A (en) | 1981-09-04 | 1981-09-04 | Low frequency filter |
Publications (1)
Publication Number | Publication Date |
---|---|
JPS5842310A true JPS5842310A (en) | 1983-03-11 |
Family
ID=15248428
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP13957481A Pending JPS5842310A (en) | 1981-09-04 | 1981-09-04 | Low frequency filter |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPS5842310A (en) |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS51137349A (en) * | 1975-05-22 | 1976-11-27 | Matsushita Electric Ind Co Ltd | Duplex quadratic type bandpass filter |
JPS5331934A (en) * | 1976-09-03 | 1978-03-25 | Sanyo Electric Co Ltd | Variable phase-shift circuit |
-
1981
- 1981-09-04 JP JP13957481A patent/JPS5842310A/en active Pending
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS51137349A (en) * | 1975-05-22 | 1976-11-27 | Matsushita Electric Ind Co Ltd | Duplex quadratic type bandpass filter |
JPS5331934A (en) * | 1976-09-03 | 1978-03-25 | Sanyo Electric Co Ltd | Variable phase-shift circuit |
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