Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2003-01-14
2004-11-02
Tra, Quan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S552000
Reexamination Certificate
active
06812780
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a fitter circuit and, more particularly, to a filter circuit having a transconductance amplifier and a detection circuit having the filter circuit.
2. Description of the Related Art
The conventional filter circuit is disclosed in “An Accurate Center Frequency Tuning Scheme for 450-khz CMOS Gm-C Bandpass Fiters”, Hiroshi Yamazaki et al, IEEE Journal of Solid State Circuits, vol. 34, No. 12, Dec. 1999.
The conventional circuit having the conventional filter circuit will be described in FIG.
5
. The conventional circuit comprises with a current outputting circuit
510
, a current-voltage transferring circuit
520
connecting to the current outputting circuit
510
and a filter circuit
530
connecting to the current-voltage transferring circuit
520
. The filter circuit
530
is a biquad bandpass filter. The filter circuit
530
has an input terminal
531
, the transconductance amplifiers
532
-
535
, the capacitors
536
,
537
and an output terminal
538
. Each transconductance amplifier has a voltage input terminal, a current input terminal and a current output terminal. The input terminal
531
is supplied with an input signal Vin of which type is voltage. The voltage input terminal of the transconductance amplifier
532
is connected to the input terminal
531
. The current input terminal of the transconductance amplifier
532
is connected to a ground node which is supplied with the ground voltage. The current output terminal of the transconductance amplifier
532
is connected to the current input terminal of the transconductance amplifier
533
, the current input terminal and the voltage input terminal of the transconductance amplifier
534
, one terminal of the capacitor
535
, the voltage input terminal of the transconductance amplifier
535
and the output terminal
538
. The current output terminal of the transconductance amplifier
533
is connected to the ground node. The voltage input terminal of the transconductance amplifier
533
is connected to the current output terminal of the transconductance amplifier
535
and one terminal of the capacitor
537
. The current output terminal of the transconductance amplifier
534
, the other terminal of the capacitor
536
, the current input terminal of the transconductance amplifier
535
and the other terminal of the capacitor
537
is connected to the ground node. The output terminal
538
outputs an output signal Vout.
Each transconductance value (the coefficient of voltage-current transfer of the transconductance amplifiers
532
-
535
is gm. The capacitors
536
,
537
have a capacitance value of C1 and C2, respectively A transfer equation T(S) of the filter circuit
530
shown in
FIG. 5
is:
T
(
s
)
=
Vout
Vin
=
s
gm
·
C2
s
2
+
s
gm
·
C2
+
1
gm
2
·
C1
·
C2
(
1
)
A transfer equation T(S) of a typical quadratic bandpass filter is:
T
(
s
)
=
ω
0
Q
s
s
2
+
ω
0
Q
s
+
ω
0
2
(
2
)
In comparison between equations [1] and [2], the filter circuit
530
operates as the bandpass filter in this example, the cutoff frequency &ohgr;0 and quality factor Q are:
ω
0
=
1
gm
·
C1
·
C2
(
3
)
Q
=
C2
C1
(
4
)
The filter circuit
530
covers scattering value of the element by adjusting the transconductance value of the transconductance amplifier, so the filter circuit
530
achieves high precision of the filter characteristics
However, the conventional circuit having the conventional filter circuit has the current-voltage transferring circuit between the current outputting circuit and the filter circuit. The input terminal Vin of the filter circuit
530
does not input current but voltage. Therefore, the circuit scale of the conventional circuit having the filter circuit becomes large and the conventional circuit requires a measurable amount of power.
In addition, the transconductances, differing from the passive element such as inductor or resistor et al., have to use within the range that the amplitude of the input signal Vin does not exceed the input dynamic range. The filter circuit has to control the amplitude of the input signal Vin. The input signal Vin includes the main signal component and the frequency component of the passing band which is the same as the main signal component Therefore, the efficiency of the filter circuit is inefficient.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a filter circuit having an input terminal which is input with a first current and which is coupled with a first nodes, a capacitor of which one terminal is coupled with the first node, of which the other terminal is coupled with a second node and which integrates the first current and outputs voltage, a transconductance means of which one terminal is coupled with the first node, of which another terminal is coupled with the second nodes of which the other terminal is coupled with a third node and which outputs a second current being proportional to the voltage to the third node and an output terminal which is coupled with the first node and which outputs the voltage.
REFERENCES:
patent: 5764100 (1998-06-01), Callicotte et al.
patent: 6181197 (2001-01-01), Bret et al.
patent: 6194959 (2001-02-01), Kamoshida et al.
patent: 2001339275 (2001-12-01), None
Oki Electric Industry Co. Ltd.
Tra Quan
Volentine Francos & Whitt PLLC
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