Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2002-10-02
2004-06-22
Phan, Trong (Department: 2818)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000, C365S173000
Reexamination Certificate
active
06754098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly to a semiconductor device having a magnetic tunnel resistance element as a resistance element.
2. Description of the Background Art
First, a constitution of a general-type filter will be discussed.
L-Shaped Primary Filter
FIGS. 39 and 40
show a low-pass filter (hereinafter, referred to as “LPF”) in which a resistor R and a capacitor C are connected to each other in the shape of L and a high-pass filter (hereinafter, referred to as “HPF”).
In
FIG. 39
, the resistor R is interposed between terminals T
1
and T
3
and the capacitor C is interposed between a wire connecting the terminals T
2
and T
4
and an end portion of the resistor R on the side of the terminal T
3
.
In
FIG. 40
, the capacitor C is interposed between the terminals T
1
and T
3
and the resistor R is interposed between the wire connecting the terminals T
2
and T
4
and an electrode of the capacitor C on the side of the terminal T
3
. Further, the terminals T
1
and T
2
serve as input terminals and the terminals T
3
and T
4
serve as output terminals.
Furthermore, as shown in
FIG. 41
, a filter in which impedances Z
1
and Z
2
are connected to each other in the shape of L is referred to as an L-shaped primary filter, which includes the constitutions of
FIGS. 39 and 40
.
The characteristic of the filter is described by transfer function representing the ratio of an output signal to an input signal of the filter and expressed by the following equation (1):
H
(
s
)
=
V
out
(
s
)
V
in
(
s
)
(
1
)
In Eq. (1), s=j&ohgr; where j represents an imaginary unit and &ohgr; represents an angular frequency.
The damping characteristic is expressed by the following equation (2):
20 log
10
|H
(j&ohgr;)|(dB) (2)
From Eq. (2), it is found that one-digit attenuation results in reduction by 20 dB (20 dB/dec).
The reason why the filter of
FIG. 41
is referred to as an L-shaped primary filter is that the denominator or numerator of the transfer function of the filter is described by the linear function of s (=j&ohgr;).
In the cases of filters of
FIGS. 39 and 40
, for example, the transfer functions H
LPF
(s) and H
HPF
(s) are expressed by the following equations (3) and (4), respectively:
H
LPF
(
s
)
=
1
sC
R
+
1
sC
=
1
1
+
sCR
(
3
)
H
LPF
(
s
)
=
R
R
+
1
sC
=
sCR
1
+
sCR
(
4
)
FIGS. 42 and 43
are schematic Bode diagrams of the LPF and the HPF. In
FIGS. 42 and 43
, the horizontal axis represents the frequency in logarithmic representation and the vertical axis represents the damping factor in logarithmic representation.
The frequency characteristic of the LPF shown in
FIG. 42
indicates that the input signal is outputted without being attenuated in a low-frequency region and the input signal is attenuated and little outputted in a high-frequency region.
On the other hand, the frequency characteristic of the HPF shown in
FIG. 43
indicates that the input signal is outputted without being attenuated in the high-frequency region and the input signal is attenuated and little outputted in the low-frequency region.
L-Shaped Secondary Filter
FIG. 44
shows an example of filter which is referred to as an L-shaped secondary filter.
In
FIG. 44
, the resistor R and an inductor L are interposed, being connected in series, between the terminals T
1
and T
3
and the capacitor C is interposed between the wire connecting the terminals T
2
and T
4
and an end portion of the inductor L on the side of the terminal T
3
.
The reason why the filter of
FIG. 44
is referred to as a secondary filter is that the denominator or numerator of the transfer function of the filter is described by the quadratic function of s (=j&ohgr;).
The filter of
FIG. 44
is an LPF, and its transfer function H(s) is expressed by the following equation (5):
H
(
s
)
=
1
sC
R
+
s
L
+
1
sC
=
1
s
2
LC
+
sRC
+
1
=
ω
p
2
s
2
+
ω
p
Q
s
+
ω
p
2
(
5
)
From the following equations (6) and (7) and the relation s=j&ohgr;, the transfer function H(s) is transformed into the equation (8) as follows:
ω
P
=
1
L
C
(
6
)
Q
=
1
R
L
C
(
7
)
H
(
s
)
=
ω
P
2
ω
P
2
-
ω
2
+
j
ω
P
Q
ω
(
8
)
From Eq. (8), it is found that the transfer function indicates the resonance characteristic when &ohgr;=&ohgr;
p
. The absolute value of the transfer function at that time is equal to Q-value (selectivity). In other words, it is preferable that the Q-value should be made as small as possible in order to suppress resonance.
FIG. 45
is a schematic view of the Bode diagram of the LPF shown in FIG.
44
.
FIG. 45
, where the horizontal axis represents the angular frequency of Eq. (6) and the vertical axis represents the damping factor, shows the Bode diagram in the cases where the Q-value is 0.8, 2 and 10.
As shown in
FIG. 45
, it is found that the characteristic of the filter is distorted near the resonance frequency &ohgr;
p
as the Q-value becomes larger.
The LPF of
FIG. 44
is represented by using the impedances Z
1
, Z
2
and Z
3
as shown in
FIG. 46
, and it is possible to form an LPF and an HPF by changing the combinations of passive elements (resistor, capacitor, inductor) which are assigned to these impedances.
The transfer function of various secondary filters is expressed, in general, by the following equations (9), (10), (11) and (12):
H
(
s
)
=
b
s
2
+
a
s
+
b
(
9
)
H
(
s
)
=
s
2
s
2
+
a
s
+
b
(
10
)
H
(
s
)
=
K
f
s
s
2
+
a
s
+
b
(
11
)
H
(
s
)
=
K
s
2
+
b
s
2
+
a
s
+
b
(
12
)
Eqs. (9) and (10) represent the transfer functions of the LPF and the HPF, respectively, and Eqs. (11) and (12) represent the transfer functions of a band-pass filter (hereinafter, referred to as “BPF”) and a band-reject filter (hereinafter, referred to as “BRF”), respectively.
Another example of the L-shaped secondary filter is such a constitution as shown in
FIG. 47
in which two L-shaped primary filters of
FIG. 41
are connected to each other.
As shown in
FIG. 47
, the impedance Z
1
is interposed between the terminals T
1
and T
3
and the impedance Z
2
is interposed between the wire connecting the terminals T
2
and T
4
and an end portion of the impedance Z
1
on the side of the terminal T
3
. Further, the impedance Z
3
is interposed between the terminal T
3
and a terminal T
5
and the impedance Z
4
is interposed between a wire connecting the terminal T
4
and a terminal T
6
and an end portion of the impedance Z
3
on the side of the terminal T
5
. The terminals T
1
and T
2
serve as input terminals and the terminals T
5
and T
6
serve as output terminals.
The filter of
FIG. 47
is also referred to as the L-shaped secondary filter since the denominator and numerator of its transfer function are described by the quadratic function.
When the passive elements are assigned so that the following relations should be satisfied, Z
1
=R
1
, Z
2
=1/sC
2
, Z
3
=R
3
and Z
4
=1/sC
4
, for example, an LPF is formed. In this case, reference signs R
1
and R
3
represent resistance values, signs C
2
and C
4
represent capacitance values and s=j&ohgr;.
Further, when the passive elements are assigned so that the following relations should be satisfied, Z
1
=1/sC
1
, Z
2
=R
2
, Z
3
=1/sC
3
and Z
4
=R
4
, for example, an HPF is formed. In this case, reference signs R
2
and R
4
represent resistance values and signs C
1
and C
3
represent capacitance values.
Furthermore, when the passive elements are assigned so that the following relations should be satisfied, Z
1
=1/sC
1
, Z
2
=R
2
, Z
3
=1/sC
3
and Z
4
=R
4
, for example, the ante-stage L-shaped filter forms an HPF and the post-stage L-shaped filter forms an LPF. The Bode diagram of this case is shown
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Phan Trong
Renesas Technology Corp.
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