Filter circuit

Details Filter circuit Filter circuit

1999-12-15

2001-02-13

Le, Dinh T. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific identifiable device, circuit, or system

Unwanted signal suppression

C327S557000, C327S558000, C330S303000, C330S306000, C333S172000

Reexamination Certificate

active

06188272

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a filter circuit, and particularly to an all-pass filter circuit for use in a delay circuit.
As is known well, filters are classified into a low pass filter (LPF), a high pass filter (HPF) and so forth depending upon which frequency is selected. The low pass filter allows a direct current (DC) signal to a signal having a predetermined frequency to pass through while preventing a signal having more than the predetermined frequency. On the other hand, the high pass filter allows signals having frequencies higher than the predetermined frequency to pass through while preventing signals having frequencies lower than the predetermined frequency.
FIG. 1A
shows a low pass filter constituted of the most simple CR (capacitor and resistance). A voltage of
FIG. 1A
is given by an equation (1)
I=(V1−V2)/R=
j
&ohgr;CV
2
  (1)
The voltage ratio between input and output is given from the equation (1) as follows:
V2/V1=1/(1
+j
&ohgr;CR)  (2)
The equation (2) is called a transfer function of the low pass filter.
FIG. 1B
is a high pass filter constituted of the most simple CR circuit. The transfer function is similarly given below:
V2/V1
=j
&ohgr;CR/(1
+j
&ohgr;CR)  (3)
On the other hand, an all-pass filter (APF) is known. The APF changes a phase or transfer time of a signal without affecting amplitude. This is used for correcting image disturbance due to distortion in phase or delay time in a wave transfer circuit of a TV tuner, VTR and the like. The transfer function is given by an equation (4):
V2/V1=(1
−j
&ohgr;CR)/(1
+j
&ohgr;CR)  (4)
In a conventionally-used integrated circuit, all pass filer (APF) is realized by forming an operation amplifier using a bipolar transistor, as shown in FIG.
2
. More specifically, signals, (Vin+Vo)/2 and (Vin/(1
+j
&ohgr;C
1
R
1
) are input to two input ports of an operation amplifier and then output (1
−j
&ohgr;C
1
R
1
)/(1
+j
&ohgr;C
1
R
1
) is obtained.
When an analog filter is realized in the recent digitalization trend in electronic appliances, it is a general way to form an integrated circuit having bipolar transistors for realizing the analog filter and MOS transistors for attaining digital processing, in combination. However, a manufacturing process of such an integrated circuit is complicated, thus increasing cost.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to attain an all-pass filter constituted of MOS or MIS transistors.
To attain the aforementioned object, the filter circuit according to a first aspect of the present invention comprises:
a first MIS transistor having a first source, a first drain, a first gate, and a channel of one conductivity type;
an input terminal connected to the first gate of the first MIS transistor;
a first power supply terminal connected to the first source of the first MIS transistor;
a second MIS transistor having a second source, a second drain, a second gate, and a channel of the one conductivity type, the second source being connected to the first drain of the first MIS transistor;
a first bias supply circuit connected to the second gate of the second MIS transistor;
a second power supply terminal connected to the second drain of the second MIS transistor;
a third MIS transistor having a third source, a third drain, a third gate, and a channel of the one conductivity type, the third source being connected to the first power supply terminal;
a resistor connected between the third gate of the third MIS transistor and the input terminal;
a capacitor connected between the third gate of the third MIS transistor and the first power supply terminal;
a fourth MIS transistor having a fourth source, a fourth drain, a fourth gate, and a channel of the one conductivity type, the fourth source being connected to the third drain of the third MIS transistor, the fourth drain being connected to the second power supply terminal, and a width/length ratio of the fourth gate being substantially ¼ of that of the third gate of the third MIS transistor;
a second bias supply circuit connected to the fourth gate of the fourth MIS transistor;
a fifth MIS transistor having a fifth source, a fifth drain, a fifth gate, and a channel of the one conductivity type, the fifth source being connected to the first power supply terminal, and the fifth gate being connected to the fourth source of the fourth MIS transistor;
an output terminal connected to the fifth drain of the fifth transistor; and
a sixth MIS transistor having a sixth source, a sixth drain, a sixth gate, and a channel of the one conductivity type, the sixth gate being connected to the second source of the second MIS transistor, the sixth source being connected to the fifth drain of the fifth MIS transistor and the output terminal, and the sixth drain being connected to the second power supply terminal.
According to the filter circuit according to a second aspect of the present invention comprises
a first MIS transistor having a first source, a first drain, a first gate, and a channel of one conductivity type;
an input terminal connected to the first gate of the first MIS transistor;
a first power supply terminal connected to the first source of the first MIS transistor;
a second MIS transistor having a second source, a second drain, a second gate, and a channel of the one conductivity type, the second source being connected to the first drain of the first MIS transistor;
a first bias supply circuit connected to the second gate of the second MIS transistor;
a second power supply terminal connected to the second drain of the second MIS transistor;
a third MIS transistor having a third source, a third drain, a third gate, and a channel of the one conductivity type, the third source being connected to the first power supply terminal;
a resistor connected between the third gate of the third MIS transistor and the input terminal;
a capacitor connected between the third gate of the third MIS transistor and the first power supply terminal;
a fourth MIS transistor having a fourth source, a fourth drain, a fourth gate, and a channel of the one conductivity type, the fourth gate being connected to the first bias supply circuit, the fourth source being connected to the third drain of the third MIS transistor, and the fourth drain being connected to the second power supply terminal;
a fifth MIS transistor having a fifth source, a fifth drain, a fifth gate, and a channel of the one conductivity type, the fifth source being connected to the first power supply terminal, and the fifth gate being connected to the third gate of the third MIS transistor;
a sixth MIS transistor having a sixth source, a sixth drain, a sixth gate, and a channel of the one conductivity type, the sixth source being connected to the fifth drain of the fifth MIS transistor, the sixth gate being connected to the fourth source of the fourth MIS transistor, and the sixth drain being connected to the second power supply terminal;
a seventh MIS transistor having a seventh source, a seventh drain, a seventh gate, and a channel of the one conductivity type, the seventh source being connected to the first power supply terminal, and the seventh gate being connected to the sixth source of the sixth MIS transistor;
an output terminal connected to the seventh drain of the seventh MIS transistor; and
an eighth MIS transistor having an eighth source, an eighth drain, an eighth gate, and a channel of the one conductivity type, the eighth gate being connected to the second source of the second MIS transistor, the eighth source being connected to the seventh drain of the seventh MIS transistor and the output terminal, and the eighth drain being connected to the second power supply terminal.
According to the present invention, the filter characteristics, which are conventionally attained by bipolar transistors, can be easily attained by MOS or MIS transistors. In the conventional method, bipolar transistors and MOS transistors a

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