GB2272812A - Active filter capable of effectively eliminating common mode noise component - Google Patents
Active filter capable of effectively eliminating common mode noise component Download PDFInfo
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- GB2272812A GB2272812A GB9323431A GB9323431A GB2272812A GB 2272812 A GB2272812 A GB 2272812A GB 9323431 A GB9323431 A GB 9323431A GB 9323431 A GB9323431 A GB 9323431A GB 2272812 A GB2272812 A GB 2272812A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/45179—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using MOSFET transistors as the active amplifying circuit
- H03F3/45197—Pl types
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/4508—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using bipolar transistors as the active amplifying circuit
- H03F3/45098—PI types
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection
-
- 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
- H03H11/0422—Frequency selective two-port networks using transconductance amplifiers, e.g. gmC filters
- H03H11/0433—Two integrator loop filters
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Networks Using Active Elements (AREA)
Abstract
An active filter includes a first stage conductance amplifier G1 having a positive-phase input terminal connected through a first resistor R1 to a first input terminal of the active filter and connected to a second resistor R2 through a connection point, and a negative-phase input terminal connected through a third resistor R3 to a second input terminal of the active filter and connected through a fourth resistor R4 to an external output terminal of the active filter. A resistance ratio of the first and second resistors is equal to a resistance ratio of the third and fourth resistors. By this, it is possible to obtain an active filter capable of removing the common mode signal component occurring as noises in a differential amplifier by using a high common mode rejection ratio (CMRR). <IMAGE>
Description
ACTIVE FILTER CAPABLE OF EFFECTIVELY
ELIMINATING COMMON MODE NOISE COMPONENT
BACKGROUND OF THE INVENTION
The present invention relates to an active filter capable of effectively realizing desired filtering characteristics by using a conductance amplifier, more particularly, to a filter circuit which passes through only signals in a low frequency band.
There has been a conventional filter circuit of such a kind described above as shown in FIG. 1. The filter circuit mainly comprises first and second conductance amplifiers G1 and G2, first and second capacitors C1 and
C2, and first and second buffer amplifiers BUF1 and BUF2.
In this case, in the first conductance amplifier G1, a positive-phase input terminal IN+ is connected with an input terminal IN for inputting an external signal, a negative-phase input terminal IN- is connected with an external output terminal OUT for outputting a signal, and an output terminal is grounded through the first capacitor C1 and at the same time connected with an input terminal of the first buffer amplifier BUF1 having a gain of "1". In the second conductance amplifier G2, a positive-phase input terminal IN+ is connected with an output terminal of the first buffer amplifier BUF1, a negative-phase input terminal IN- is connected with the external output terminal OUT, and an output terminal is grounded through the second capacitor C2 and at the same time is connected with an input terminal of the second buffer amplifier BUF2 having a gain of "1".An output terminal of the second buffer amplifier BUF2 is also connected with the external output terminal OUT.
Since the gains of the first and second buffer amplifiers BUF1 and BUF2 are "1", respectively, an output of the first conductance amplifier G1 becomes the an input of the second conductance amplifier G2, and an output of the second conductance amplifier G2 is outputted by the external output terminal OUT.
Accordingly, if conductances of the first and second conductance amplifiers G1 and G2 are gml and gm2, respectively, a transmission function of the filter circuit can be represented by the following equation (1):
T(s) = VOUT / VIN = {(gm1.gm2)/(C1.C2)}/{s2+(gm2/C2)s+(gm1-gm2)/(C1.C2))
(1) where VIN is a voltage of the input terminal IN, VOUT is the external output terminal OUT, C1 is an electrostatic capacity of the capacitor C1, and C2 is an electrostatic capacity of the capacitor C2.
On the other hand, a general equation of a transmission function of the secondary low-pass filter can be represented by the following equation (2):
T(s) = wo2 / (s2+(0/Q)s+w02) (2)
Accordingly, it can be understood that the filter circuit shown in FIG. 1 is the secondary low-pass filter.
Here, situations represented by equations (3) and (4): = = f(gm1.gm2)/(C1.C2)}112 (3) Q = {(grn1/gm2).(C1/C2))l/2 (4) As being well known, the differential output type amplifier has a positive output terminal and a negative output terminal. When a superposed output of "Vl+VN11 is outputted under the condition where a voltage V1 is a differential component from the positive output terminal as a reference of the grounded level and a noise component such as a power source ripple and the like, namely, a noise component VN has various frequency components, the negative output terminal outputs "-V1+V,"r where the noise component VN is called as a common mode noise component.
When one terminal output of the differential amplifier A1 (namely, V1+VN) is supplied to the input terminal IN of the filter circuit, even though the filter removes a component having a frequency higher than a cut off frequency f in the noise component VN, the filter does not remove a component having a frequency lower than the cut-off frequency f so as to output it from the external output terminal OUT.
Accordingly, the conventional filter circuit shown in FIG. 1 has the problem that it is impossible to remove a common mode noise component included in the outputs of the differential amplifier and the like.
SUMMARY OF THE INVENTION
In order to solve the above problem, an object of the present invention is to provide a filter circuit capable of removing a common mode (in-phase) noise component by using a common mode rejection ratio (CMRR) having a high value.
An active filter according to the present invention, having a first input terminal, a second input terminal and an external output terminal, comprises a first conductance amplifier having a first positive-phase input terminal electrically connected to the first input terminal, a first negative-phase input terminal electrically connected to the second input terminal, and an output terminal electrically connected to the external output terminal; a first capacitor connected between the first output terminal and a terminal of a predetermined potential; a first resistor connected between the first input terminal and the first positive-phase input terminal; a second resistor connected between the first positive-phase input terminal and the terminal of the predetermined potential; a third resistor connected between the second input terminal and the first negativephase input terminal; and a fourth resistor connected between the external output terminal and the first negative-phase input terminal: wherein a resistance value ratio of the first and second resistors is substantially equal to a resistance value ratio of the third and fourth resistors.
A filter circuit as an aspect of the present invention comprises the first conductance amplifier; the first capacitor; a second conductance amplifier having a second positive-phase input terminal electrically connected to the first output terminal, a second negative-phase input terminal electrically connected to the second input terminal through the third and fourth resistors, and a second output terminal electrically connected to the external output terminal; a second capacitor connected to the second output terminal and the terminal of the predetermined potential: wherein a resistance value ratio of the first and second resistors us substantially equal to a resistance value ratio of the third and fourth resistors.
In the present invention, the positive-phase input terminal of the conductance amplifier is connected to the first input terminal through the first resistor, and grounded to the earth through the second resistor. On the other hand, the first negative-phase terminal is connected to the second input terminal through the third resistor and to the external output terminal through the fourth resistor. Furthermore, the resistance ratio of the first and second resistors is substantially equal to that of the third and fourth resistors, thereby supplying one of signals having the common mode signal component to the first input terminal and the other of signals to the second input terminal. Accordingly, a differential signal component is transmitted to the external output terminal and the common mode (in-phase) signal component does not appear on the external output terminal, thereby removing the common mode signal component by using a higher CMRR.
As being clarified from the above description, since the differential signal component is transmitted to the external output terminal and the common mode signal component does not appear to the external output terminal, it is possible to remove the common mode signal component by using the higher CMRR.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a circuit diagram showing a configuration of the conventional filter circuit;
FIG. 2 is a circuit diagram showing a configuration of a filter circuit according to a first embodiment of the present invention;
FIG. 3 is a circuit diagram showing a filter circuit according to a second embodiment of the present invention as a detailed structure of the filter circuit of the first embodiment;
FIG. 4 is a circuit diagram showing a donfiguration of a filter circuit according to a third embodiment of the present invention;
FIG. 5 is a circuit diagram showing a filter circuit according to a fourth embodiment of the present invention as a detailed structure of the filter circuit of the third embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
There will be described in detail active filters according to preferred embodiments of the present invention in reference with the attached drawings.
FIG. 2 is a circuit diagram showing a circuit configuration according to a first embodiment of the present invention. In this figure, elements attached by the same numeral in FIG. 1 are the same components in the conventional filter circuit.
An active filter according to the first embodiment comprises first and second input terminals IN1 and IN2.
The first input terminal IN1 is connected to one end of a first resistor R1 having the other end connected to a positive-phase input terminal IN+ of a first conductance amplifier G1 which is also connected in parallel with a second resistor R2. The other end of the second resistor
R2 is grounded to the earth. On the other hand, the second input terminal IN2 is connected to one end of a third resistor R3 having the other end connected to a negative-phase input terminal IN- of the first conductance amplifier G1. The negative-phase input terminal IN- of the conductance amplifier G1 is also connected to one end of a fourth resistor R4 having the other end connected to an external output terminal.
Since the configuration from the first conductance amplifier G1 to the external output terminal OUT is constructed in the same manner of the configuration shown in FIG. 1, there will be omitted the detailed description.
There is described operation of the active filter according to the first embodiment of the present invention described above.
In the case where the common mode signal component is added to the first and second input terminals IN1 and
IN2, a signal existing in a positive-phase input terminal of a differential amplifier A1 is supplied to the first input terminal IN1, and a signal existing in a negativephase input terminal of the differential amplifier A1 is supplied to the second input terminal IN2. At this time, a voltage VOUT is obtained in the external output terminal by the following equation (5):
where R1 means a resistance value of the resistor
R1, R2 means a resistance value of the resistor R2, R3 means a resistance value of the resistor R3, and R4 means a resistance value of the resistor R4.
Here, the first through fourth resistors R1-R4 use the resistance value having the relationship obtained by the equation (6):
R1/R2 = R3/R4 ...... (6)
By using the relationship of the equation (6), the equation (5) can be changed an equation (7):
Here, in order easy to be understood, an equation (8) shows a transmission function T(s) in the case where a differential signal VIN/2 is supplied to the input terminal IN1 and a differential signal -VIN/2 is supplied to the input terminal IN2:
where A is R2/R1.
Since a general equation of the transmission function of the secondary low-pass filter is obtained by the equation (2), the filter circuit is the secondary low-pass filter having the gain of "A" and coO and Q obtained by the following equations (9) and (10) as being easily understood by comparing the equations (2) and (8): coo = [{(gm1.gm2)/(C1.C2))(R1/(R1+R2)}] (9)
Q = [(gm1/gm2).(C1/C2).{R1/(R1+R2)}] (10)
Next, when the input terminals IN1 and IN2 receive the common mode signal component, there is "VoUT = O as clarified from the equation (7).
As a result, if the input terminal IN1 receives the signal VIN/2+VN which appears at the positive output terminal of the differential amplifier and the input terminal IN2 receives the signal -VIN/2+VN which appears at the negative output terminal of the differential amplifier, the differential signal component VIN is transmitted to the external output terminal OUT according to the equation (8), but the common mode component VN is not supplied to the external output terminal.
Accordingly, the filter circuit shown in FIG. 2 can be determined as a secondary low-pass filter having a higher common mode rejection ratio (CMRR).
As a specified case, if the condition of "R1/R2=R3/R4=l" is satisfied, there is A=1, thereby representing the transmission function in a simple form according to an equation (11):
0 and Q at this time are obtained by the following equations (12) and (13): coo = {(gml-gm2)/(2ClC2)}l/2 (12)
Q = {(gm1/gm2).(C2/C1)/2}l/2 ..... (13) In the above embodiment, even though both of the buffer amplifiers BUF1 and BUF2 are used, the buffer amplifier BUF1 can be cancelled when the an input impedance of the conductance amplifier G2 is sufficient to be high. Furthermore, the buffer amplifier BUF2 also can be cancelled when an input impedance of a load circuit connected to the external output terminal OUT is sufficient to be high.
Even though the input terminal IN1 receives the signal which appears at the positive output terminal of the differential amplifier and the input terminal IN2 receives the signal which appears at the negative output terminal of the differential amplifier in the abovementioned embodiment, the signals supplied to the input terminals IN1 and IN2 are limited in the output signals of the differential amplifier. It is needless to say that it is possible to remove the common mode signal component by supplying one of signals including the common mode component to the input terminal IN1 and the other signal to the input terminal IN2.
Furthermore, even though the negative-phase input terminal IN- of the conductance amplifier G2 is connected to the external output terminal OUT to directly supply a voltage occurring at the external output terminal OUT to the negative-phase input terminal IN- of the conductance amplifier G2, it is possible to perform same operation by adding common use means for changing a value of Q, namely, signal attenuation means for attenuating a voltage of the output terminal to supply an attenuated voltage to the negative-phase input terminal of the conductance amplifier G2.
FIG. 3 shows a second embodiment as a detailed construction of the present invention. In the figure, the conductance amplifier G1 comprises transistors Q1, Q2 Q6' Q7 Q8 and Qg and diodes Q3, Q4 and Q5, and the conductance amplifier G2 comprises transistors 011, Q12, 416' Q17t Q18 and Qlg and diodes Q13 Q14 and Q15 A transistor Qlo is used as the buffer amplifier BUF1 and a transistor Q20 is used as the buffer amplifier BUF2.
Since the conductance amplifiers G1 and G2 have the same constitution each other, there is described duplicate operation with respect to a conductance amplifier G1.
Emitters of the transistors Q1 and Q2 are connected with each other through a resistor to form a differential amplifier circuit, and the diodes Q3 and Q4 are loads of the transistors. Emitters of the transistors Q1 and Q2 are connected with each other to form a differential amplifier circuit. The transistors Q8 and Qg which are respectively connected with collectors of the respective transistors Q6 and Q7, have emitters which are connected with each other to form a current mirror load. Anodes of the diodes Q3 and Q4 are connected in parallel with each other, and its connecting point thereof is connected with a cathode of the diode Q5 having an anode connected to a constant voltage source Vcc.
When a signal level increases at the input terminal
IN1, a current flowing in the transistor Q1 increases, and on the contrary, a current flowing in the transistor
Q2 decreases. Accordingly, a collector voltage of the transistor Q1 falls down, and a collector voltage of the transistor Q2 rises. In accordance with this, a current flowing in the transistor Q6 increases, and a current flowing in the transistors Qg increases with the same rate. As a result, a differential component between a current flowing to the transistor Qg and a current flowing to the transistor Q7 flows into the capacitor C1 in which an occurring voltage causes the transistor Qlo as the buffer amplifier to increase a base current.
In contrast with this, when the signal level to supply to the input terminal IN1 decreases, the base voltage of the transistor Qlo decreases in the manner of operation opposite to the above operation.
As a result, it is possible to easily realize the filter circuit shown in FIG. 2.
Even though the first and second embodiment shown in
FIGS. 2 and 3 relate to the secondary low-pass filter, the present invention is not limited in these cases. The present invention may have the following constitution of a primary low-pass filter. The input terminal IN1 is connected through the first resistor to the positivephase input terminal of the first conductance amplifier, and the second resistor is connected between a connecting point of the first resistor and the positive-phase input terminal and grounded to the earth. The third resistor is connected between the negative-phase input terminal of the first conductance amplifier and the second input terminal, and the fourth resistor is connected between a connecting point of the third resistor and the negative input terminal and the external output terminal.
Furthermore, a resistance value of the first and second resistors is equal to a resistance value of the third and fourth resistors, thereby removing the common mode signal component.
There is described more detail a third embodiment of the primary low-pass filter with reference to FIG. 4.
FIG. 4 is a circuit diagram showing an active filter according to the third embodiment of the present invention. in this figure, elements represented by the numeral as the same as those of the filter shown in FIG.
2 are the same components of the first embodiment. In
FIG. 4, the second conductance amplifier G2, the second capacitor C2 and the second buffer BUF2 are eliminated, and the output terminal of the first buffer amplifier
BUF1 is connected to the external output terminal OUT.
In this case, since the conductance amplifier, the buffer amplifier and the capacitor are respectively provided one, a symbol of the first conductance amplifier is changed from G1 to G, the first buffer amplifier from
BUF1 to BUF, and the first capacitor from C1 to C.
In FIG. 4, when a voltage V1 is supplied to the input terminal IN1 and a voltage V2 is supplied to the input terminal IN2, respectively, a voltage VOUT occurring at the external output terminal OUT can be obtained by an equation (14) as follows:
where R1 is a resistance value of the resistor R1,
R2 is a resistance value of the resistor R2, R3 is a resistance value of the resistor R3, R4 is a resistance value of the resistor R4, gm is a conductance of the conductance amplifier G, and C is a capacitance of the capacitor C.
Here, if the relationship of R1/R2=R3/R4 is held water, the equation (14) can be changed into an equation (15) as follows:
Furthermore, when the differential signal component
VIN/2 is supplied to the input terminal IN1 and the differential signal component VIN/2 is supplied to the input terminal IN2, respectively, the transmission function T(s) can be obtained by the following equation (16):
where A is R2/R1.
A general equation of the transmission function of the primary low-pass filter is generally represented by the following equation (17):
T(s) = coo / (s+co0) @ (17)
Accordingly, the circuit shown in FIG. 4 is understood as the primary low-pass filter which has a gain of "A" and the relationship of "coo = {R1/(R1+R2)).gm/C".
Next, when the common mode signal component VN is supplied to the input terminals IN1 and IN2, respectively, there is VOUT=O as clarified from the equation (13).
As a result, if VIN/2+VN is supplied to the input terminal IN1, -VIN/1+VN is supplied to the input terminal
IN2, the differential signal component VIN is transmitted to the external output terminal OUT according to the equation (13), and the common mode component VN does not appear at the external output terminal OUT. Accordingly, the filter circuit shown in FIG. 4 is also the filter having a high common mode rejection ratio (CMRR).
Even though the third embodiment uses the buffer amplifier BUF, if the resistance value of the resistor R4 is sufficient to be large and the input impedance of the load circuit connected to the external output terminal is sufficient to be high, it is possible to remove the buffer amplifier BUF.
Furthermore, even though the third embodiment does not have common use means for changing a value of O, namely, signal attenuation means for attenuating a voltage of the output terminal and supplying the voltage to the negative-phase input terminal of the conductance amplifier G, the present invention may comprises the signal attenuation means for performing operation as the same as described above.
Even though the detailed construction of the conductance amplifier G and the buffer amplifier BUF of the third embodiment should be conceived from the configuration shown in FIG. 3, a detailed construction of these elements is shown as a fourth embodiment by way of precaution.
In FIG. 5, since the conductance amplifier, the buffer amplifier and the capacitor are respectively provided one, a symbol of the first conductance amplifier is changed from G1 to G, the first buffer amplifier from
BUF1 to BUF, and the first capacitor from C1 to C.
In the figure, the conductance amplifier G comprises transistors Q1 Q2 Q6 Q7 Q8 and Qg and diodes Q3, Q4 and Q5, and a transistor Qlo is used as the buffer amplifier BUF.
Since the conductance amplifier G has the same constitution as that in the second embodiment, there is described duplicate operation with respect to a conductance amplifier G.
Emitters of the transistors Q1 and Q2 are connected with each other through a resistor to form a differential amplifier circuit, and the diodes Q3 and Q4 are loads of the transistors. Emitters of the transistors Q1 and Q2 are connected with each other to form a differential amplifier circuit. The transistors Q8 and Qg which are respectively connected with collectors of the respective transistors Q6 and Q7, have emitters which are connected with each other to form a current mirror load. Anodes of the diodes Q3 and Q4 are connected in parallel with each other, and its connecting point thereof is connected with a cathode of the diode Q5 having an anode connected to a constant voltage source Vcc.
When a signal level increases at the input terminal
IN1, a current flowing in the transistor Q1 increases, and on the contrary, a current flowing in the transistor Q2 decreases. Accordingly, a collector voltage of the transistor Ql falls down, and a collector voltage of the transistor Q2 rises. In accordance with this, a current flowing in the transistor Q6 increases, and a current flowing in the transistors Qg increases with the same rate. As a result, a differential component between a current flowing to the transistor Qg and a current flowing to the transistor Q7 flows into the capacitor C1 in which an occurring voltage causes the transistor Qlo as the buffer amplifier to increase a base current.
In contrast with this, when the signal level to supply to the input terminal IN1 decreases, the base voltage of the transistor Qlo decreases in the manner of operation opposite to the above operation.
As a result, it is also possible to easily realize the filter circuit shown in FIG. 5.
Claims (7)
1. An active filter with a first input terminal, a second input terminal, and an external output terminal, the active filter comprising:
a first conductance amplifier having a first positive-phase input terminal electrically connected to said first input terminal, a first negative-phase input terminal electrically connected to said second input terminal, and a first output terminal electrically connected to said external output terminal;
a first capacitor connected between said first output terminal and a terminal of a predetermined potential;
a first resistor connected between ' said first input terminal and said first positive-phase input terminal;
a second resistor connected between said first positive-phase input terminal and the terminal of the predetermined potential;
a third resistor connected between said second input terminal and said first negative-phase input terminal; and
a fourth resistor connected between said external output terminal and said first negative-phase input terminal:
wherein a resistance value ratio of said first and second resistors is substantially equal to a resistance value ratio of said third and fourth resistors.
2. The active filter according to claim 1, further comprising:
a second conductance amplifier having a second positive-phase input terminal electrically connected to the first output terminal, a second negative-phase input terminal connected to the external output terminal, and a second output terminal electrically connected to the external output terminal; and
a second capacitor connected between said second output terminal and the terminal of the predetermined potential:
wherein said first output terminal of the first conductance amplifier is electrically connected to the external output terminal via said second conductance amplifier.
3. The active filter according to claim 2, further comprising
a first buffer connected between said first output terminal and said second positive-phase input terminal; and
a second buffer connected between said second output terminal and said external output terminal.
4. The active filter according to claim 2, wherein said first conductance amplifier comprises
a first differential amplifier including first and second transistors of which both emitters are connected with each other through a resistor, and bases are connected to said first positive-phase and first negative-phase input terminals, respectively;
a diode connection body including first and second diodes of which both cathodes are connected to collectors of said first and second transistors, respectively, and a third diode of which a cathode is connected to both anodes of said first and second diodes;;
a second differential amplifier including a third transistor having a base connected to the collector of said second transistor, a fourth transistor having a base connected to the collector of said first transistor, and said third and fourth transistors of which both emitters are connected with each other to the terminal of the predetermined potential through a constant current source; and
a current mirror circuit including fifth and sixth transistors of which collectors are connected to collectors of said third and fourth transistors, respectively, and of which both bases are connected with each other:
and wherein said second conductance amplifier comprises
a third differential amplifier including seventh and eighth transistors of which both emitters are connected with each other through a resistor, said seventh transistor of which a base is connected to said output terminal of said first conductance amplifier, and said eighth transistor of which a base is connected to said second input terminal;
another diode connection body including fourth and fifth diodes of which both cathodes are respectively connected to collectors of said fourth and fifth transistors, and a ninth diode of which a cathode is connected to both anodes of said fourth and fifth diodes;;
a fourth differential amplifier including a ninth transistor having a base connected to said eighth transistor, a tenth transistor having a base connected to said first transistor, and said ninth and tenth transistors of which both emitters are connected with each other to the terminal of the predetermined potential through a constant current source; and
another current mirror circuit including ninth and tenth transistors of which collectors are connected to collectors of said ninth and tenth transistors, respectively, and of which both bases are connected with each other.
5. The active filter according to claim 1, further comprising
a first buffer connected between said first output terminal and said external output terminal.
6. The active filter according to claim 5, wherein said first conductance amplifier comprises
a first differential amplifier including first and second transistors of which both emitters are connected with each other through a resistor, and bases are connected to said first positive-phase and first negative-phase input terminals, respectively;
a diode connection body including first and second diodes of which both cathodes are connected to collectors of said first and second transistors, respectively, and a third diode of which a cathode is connected to both anodes of said first and second diodes; ;
a second differential amplifier including a third transistor having a base connected to said second transistor, a fourth transistor having a base connected to the collector of said first transistor, and said third and fourth transistors of which both emitters are connected with each other to the terminal of the predetermined potential through a constant current source; and
a current mirror circuit including fifth and sixth transistors of which collectors are connected to collectors of said third and fourth transistors, respectively, and of which both bases are connected with each other.
7. An active filter substantially as hereinbefore described with reference to Figures 2 to 5 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP04302525A JP3108551B2 (en) | 1992-11-12 | 1992-11-12 | Filter circuit |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9323431D0 GB9323431D0 (en) | 1994-01-05 |
| GB2272812A true GB2272812A (en) | 1994-05-25 |
| GB2272812B GB2272812B (en) | 1996-01-10 |
Family
ID=17910018
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9323431A Expired - Fee Related GB2272812B (en) | 1992-11-12 | 1993-11-12 | Active filter capable of effectively eliminating common mode noise component |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JP3108551B2 (en) |
| KR (1) | KR940012818A (en) |
| GB (1) | GB2272812B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0633714U (en) * | 1992-10-09 | 1994-05-06 | 関東自動車工業株式会社 | Car door compartment |
| US7272187B2 (en) | 2002-11-01 | 2007-09-18 | Matsushita Electric Industrial Co., Ltd. | Filter circuit and radio apparatus |
| JP5070918B2 (en) * | 2007-05-01 | 2012-11-14 | 富士通セミコンダクター株式会社 | Analog signal selection circuit |
| US8049562B2 (en) * | 2010-01-07 | 2011-11-01 | Texas Instruments Incorporated | Amplifier with improved input resistance and controlled common mode |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3832646A (en) * | 1972-10-06 | 1974-08-27 | Westinghouse Electric Corp | Common mode noise suppressing circuit adjustment sequence |
-
1992
- 1992-11-12 JP JP04302525A patent/JP3108551B2/en not_active Expired - Fee Related
-
1993
- 1993-11-09 KR KR1019930023664A patent/KR940012818A/en not_active Application Discontinuation
- 1993-11-12 GB GB9323431A patent/GB2272812B/en not_active Expired - Fee Related
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3832646A (en) * | 1972-10-06 | 1974-08-27 | Westinghouse Electric Corp | Common mode noise suppressing circuit adjustment sequence |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH06152318A (en) | 1994-05-31 |
| GB9323431D0 (en) | 1994-01-05 |
| KR940012818A (en) | 1994-06-24 |
| JP3108551B2 (en) | 2000-11-13 |
| GB2272812B (en) | 1996-01-10 |
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|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20111112 |