JPH0323011B2 - - Google Patents
Info
- Publication number
- JPH0323011B2 JPH0323011B2 JP8402284A JP8402284A JPH0323011B2 JP H0323011 B2 JPH0323011 B2 JP H0323011B2 JP 8402284 A JP8402284 A JP 8402284A JP 8402284 A JP8402284 A JP 8402284A JP H0323011 B2 JPH0323011 B2 JP H0323011B2
- Authority
- JP
- Japan
- Prior art keywords
- voltage source
- feedback amplifier
- circuit
- amplifier
- varicap
- 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
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H11/00—Networks using active elements
- H03H11/02—Multiple-port networks
- H03H11/04—Frequency selective two-port networks
- H03H11/12—Frequency selective two-port networks using amplifiers with feedback
- H03H11/1213—Frequency selective two-port networks using amplifiers with feedback using transistor amplifiers
Landscapes
- Networks Using Active Elements (AREA)
Description
【発明の詳細な説明】
〔発明の利用分野〕
本発明は、シリコンウエハ上などに形成するモ
ノリシツクIC内にフイルタを集積する場合に適
したフイルタ集積回路に関するものである。DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a filter integrated circuit suitable for integrating a filter in a monolithic IC formed on a silicon wafer or the like.
電気回路の集積化（モノリシツクIC化、以下
単にIC化と略す）が進むにつれ、外付けのブロ
ツクフイルタのIC化が回路の小形化、低コスト
化を実現する上で重要な課題となりつつある。従
来のフイルタは大部分がインダクタンスＬ、容量
Ｃ、抵抗Ｒで構成されているが、インダクタンス
ＬはIC化が困難である。したがつて、抵抗Ｒ、
容量Ｃで構成可能なアクテイブフイルタがIC化
には適している。特にローパスフイルタ（以下
LPFと略す）としては、第１図に示す帰還型
LPFが良く知られている。同図において、１は
ゲインがＫの増幅器、R1とR2は抵抗、C1とC2は
容量、２は信号源、Viは信号入力端、Voは信号
出力端である。同回路において、共振周波数0は
で表わされ、回路の良さを表わすＱは、
で与えられる。斯る構成のLPFをIC化する場合、
ばらつきの問題が生じる。即ちIC内の容量値、
抵抗値は不純物濃度やマスクずれなどの影響を受
け、一例として、
Ｃの絶対値 ±20％
Ｒの絶対値 ±15％
などの大きな変動を有する。したがつて第１図に
示すLPFの共振周波数0は式(1)より第２図の様に
ａからｂの範囲で変動し、最悪±35％変動するこ
とになり、実用化は困難である。この対策として
は、ICチツプ上でレーザートリミングなどによ
り抵抗値を変化させ、ばらつき吸収を行なうこと
も実施されているが、精度、歩留り、コストの面
などでまだ多くの問題があり、一般民生用ICに
はほとんど採用されていない。
As the integration of electrical circuits (monolithic ICs, hereinafter simply referred to as ICs) progresses, the use of ICs for external block filters is becoming an important issue in achieving smaller circuits and lower costs. A conventional filter is mostly composed of an inductance L, a capacitance C, and a resistance R, but it is difficult to integrate the inductance L into an IC. Therefore, the resistance R,
An active filter that can be configured with a capacitance of C is suitable for IC implementation. Especially the low pass filter (below
(abbreviated as LPF), the feedback type shown in Figure 1 is
LPF is well known. In the figure, 1 is an amplifier with a gain of K, R 1 and R 2 are resistors, C 1 and C 2 are capacitors, 2 is a signal source, Vi is a signal input terminal, and Vo is a signal output terminal. In the same circuit, the resonant frequency 0 is Q, which represents the goodness of the circuit, is is given by When converting an LPF with such a configuration into an IC,
The problem of variation arises. In other words, the capacitance value inside the IC,
The resistance value is affected by impurity concentration, mask misalignment, etc., and has large fluctuations such as, for example, the absolute value of C ±20% and the absolute value of R ±15%. Therefore, the resonant frequency 0 of the LPF shown in Figure 1 fluctuates in the range from a to b as shown in Figure 2 from equation (1), and at worst it fluctuates by ±35%, making it difficult to put it into practical use. . As a countermeasure to this problem, attempts have been made to change the resistance value on the IC chip by laser trimming etc. to absorb variations, but there are still many problems in terms of accuracy, yield, cost, etc. It is rarely used in ICs.
本発明の目的は、上記した欠点を取り除くフイ
ルタ回路を提供することにある。
The object of the invention is to provide a filter circuit which eliminates the above-mentioned drawbacks.
本発明は帰還増幅器として用いる差動入力を有
する増幅器とバリキヤツプ及び抵抗より構成され
る帰還型LPF回路において、反転入力端と非反
転入力端の２入力端に印加する直流電圧を同時に
変化させることにより、増幅器出力端の直流電圧
を一定にし、非反転入力端と同一の直流電圧が印
加された時定数回路と増幅器の出力端との間に接
続されたバリキヤツプと時定数回路と電圧源の間
に接続されたバリキヤツプの印加電圧を変化させ
容量値を変化させるものである。
The present invention is a feedback type LPF circuit composed of an amplifier having a differential input used as a feedback amplifier, a varicap, and a resistor. , the DC voltage at the output terminal of the amplifier is kept constant, and the variable cap is connected between the time constant circuit and the output terminal of the amplifier to which the same DC voltage as the non-inverting input terminal is applied, and between the time constant circuit and the voltage source. The capacitance value is changed by changing the voltage applied to the connected variable cap.
以下、本発明の一実施例を第３図により説明す
る。同図の回路において、R1，R2及び７，８，
９は抵抗、C1とC2はバリキヤツプ、Q1とQ2はト
ランジスタ、１０はゲインがK1の演算増幅器、
１１，１２は電流源、V6は可変電圧源、V7は電
圧源、１３はバツフア回路、１４は調整端子であ
る。ｅ点及びｆ点の直流電位Ve，Vfは
Ve＝Vf＝V6−VBE
である。VBEはトランジスタのベース、エミツタ
間の電位差である。可変電圧源V6を△V6変化さ
せた場合、Ve，Vfは
Ve＝Vf＝V6＋△V6−VBE
となり、可変電圧源V6が変化しても、Ve＝Vfな
ので、１０の増幅器出力端の直流電位Vgは常に
一定である。したがつてバリキヤツプC1の両端
の電位差VC1は、
VC1＝Vg−Ve
＝Vg−（V6−VBE
となり、可変電圧源V6が△V6変化すると、
VC1＝Vg−（V6＋△V6−VBE）
となる。バリキヤツプC2、の両端の電位差VC2
は、
VC2＝V7−（V6−VBE）
となり、V6が△V6変化すると
VC2＝V7−（V6＋△V6−VBE）
となる。上記の様に14の調整端子に接続された可
変電圧源V6のみの調整によりバリキヤツプC1，
C2の両端の電位差は同一の変化をする。したが
つて、電圧源V7を増幅器１０の出力端直流電位
Ｖにほぼ等しくすると、バリキヤツプC1，C2の
容量値は同一量変化する。即ち式(1)、式(2)より、
回路の良さを表わすＱを変化させることなく、共
振周波数0のみを変化させることが可能である。
An embodiment of the present invention will be described below with reference to FIG. In the circuit of the same figure, R 1 , R 2 and 7, 8,
9 is a resistor, C 1 and C 2 are varicaps, Q 1 and Q 2 are transistors, 10 is an operational amplifier with a gain of K 1 ,
11 and 12 are current sources, V 6 is a variable voltage source, V 7 is a voltage source, 13 is a buffer circuit, and 14 is an adjustment terminal. The DC potentials Ve and Vf at point e and point f are Ve=V f =V 6 −V BE . V BE is the potential difference between the base and emitter of the transistor. When variable voltage source V 6 is changed by △V 6 , Ve, Vf become Ve=Vf=V 6 +△V 6 −V BE , and even if variable voltage source V 6 changes, Ve=Vf, so 10 The DC potential Vg at the output end of the amplifier is always constant. Therefore, the potential difference V C1 across the varicap C 1 becomes V C1 = Vg - Ve = Vg - (V 6 - V BE , and when the variable voltage source V 6 changes by △V 6 , V C1 = Vg - (V 6 +△V 6 −V BE ).The potential difference across the varicap C 2 , V C2
is V C2 = V 7 − (V 6 − V BE ), and when V 6 changes by △V 6 , V C2 = V 7 − (V 6 + △V 6 − V BE ). Varicap C 1 , by adjusting only the variable voltage source V 6 connected to the 14 adjustment terminals as described above.
The potential difference across C 2 changes in the same way. Therefore, when the voltage source V 7 is made approximately equal to the output terminal DC potential V of the amplifier 10, the capacitance values of the variable caps C 1 and C 2 change by the same amount. That is, from equations (1) and (2),
It is possible to change only the resonance frequency 0 without changing Q, which represents the quality of the circuit.
また、可変電圧源V6に基くバリキヤツプの印
加電圧は帰還増幅器ゲインとは無関係であるの
で、異なるゲインの帰還増幅器を用いた同形式の
フイルタ回路と調整端子を共通にすることも可能
である。 Furthermore, since the voltage applied to the variable cap based on the variable voltage source V6 is independent of the feedback amplifier gain, it is also possible to share the adjustment terminal with a filter circuit of the same type using a feedback amplifier with a different gain.
以上説明した様に、本発明によるLPF回路で
は、容量にバリキヤツプを用い、その印加電圧を
外部調整端子により調整することによりバリキヤ
ツプの容量値を変化させ、時定数ばらつきを吸収
し、所望のLPF特性を得ることが可能となる。
従来外付部品であつたブロツクフイルタをIC化
でき、回路の小形化、低コスト化に有効である。
As explained above, in the LPF circuit according to the present invention, a varicap is used as the capacitor, and the applied voltage is adjusted by an external adjustment terminal to change the capacitance value of the varicap, absorb time constant variations, and achieve desired LPF characteristics. It becomes possible to obtain.
The block filter, which was conventionally an external component, can be integrated into an IC, which is effective in reducing the size and cost of the circuit.
第１図は、２次の正帰還型LPFの一例を示す
回路図、第２図は、LPFの振幅特性の一例を示
す特性図、第３図は、本発明のフイルタ回路の一
実施例を示す回路図である。
C1，C2…バリキヤツプ、R1，R2…抵抗、１０
…増幅器、１４…調整端子、V6…可変電圧源、
V7…電圧源。
Fig. 1 is a circuit diagram showing an example of a secondary positive feedback type LPF, Fig. 2 is a characteristic diagram showing an example of the amplitude characteristics of the LPF, and Fig. 3 is an example of a filter circuit of the present invention. FIG. C 1 , C 2 ... Varicap, R 1 , R 2 ... Resistance, 10
…Amplifier, 14…Adjustment terminal, V6 …Variable voltage source,
V 7 ...voltage source.
Claims (1)
１の抵抗と差動入力を有する帰還増幅器の非反転
入力端との間に接続された第２の抵抗と、該帰還
増幅器の出力端と第１及び第２の抵抗の接続点と
の間に接続された第１のバリキヤツプと帰還増幅
器の非反転入力端と定電圧源との間に接続された
バリキヤツプと、帰還増幅器の反転入力端に接続
された直流バイアス回路と、可変電圧源とからな
り、可変電圧源の電位を帰還増幅器の２入力端に
印加し、第１と第２のバリキヤツプの印加電圧を
変化させることを特徴とするフイルタ回路。1 a first resistor connected to a signal input terminal, a second resistor connected between the first resistor and a non-inverting input terminal of a feedback amplifier having a differential input, and an output of the feedback amplifier; a first varicap connected between the end and the connection point of the first and second resistors, a varicap connected between the non-inverting input end of the feedback amplifier and a constant voltage source, and an inverting input of the feedback amplifier. It consists of a DC bias circuit connected to one end and a variable voltage source, and is characterized in that the potential of the variable voltage source is applied to two input ends of the feedback amplifier to change the voltage applied to the first and second varicaps. filter circuit.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8402284A JPS60229418A (en) | 1984-04-27 | 1984-04-27 | Filter circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8402284A JPS60229418A (en) | 1984-04-27 | 1984-04-27 | Filter circuit |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS60229418A JPS60229418A (en) | 1985-11-14 |
| JPH0323011B2 true JPH0323011B2 (en) | 1991-03-28 |
Family
ID=13818938
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP8402284A Granted JPS60229418A (en) | 1984-04-27 | 1984-04-27 | Filter circuit |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS60229418A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5625316A (en) * | 1994-07-01 | 1997-04-29 | Motorola, Inc. | Tuning circuit for an RC filter |
-
1984
- 1984-04-27 JP JP8402284A patent/JPS60229418A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS60229418A (en) | 1985-11-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| LAPS | Cancellation because of no payment of annual fees |