Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2002-08-19
2004-08-03
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S540000, C327S546000, C323S313000, C323S316000
Reexamination Certificate
active
06771117
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a semiconductor device. More particularly, the present invention relates to a semiconductor device having a voltage down-converter.
2. Description of the Background Art
Recently, transistors for use in semiconductor devices are increasingly miniaturized in order to implement reduced costs, reduced power consumption and increased operation speed. A power supply potential must be reduced in order to ensure reliability of the miniaturized transistors.
A semiconductor device is a fundamental component that is used together with various components in various equipments. However, reduction in voltage has not been implemented for most other components that are used in equipments including a semiconductor device. In view of matching between a semiconductor device and other components, a semiconductor device using a miniaturized transistor must operate with an external power supply potential that is high enough to degrade reliability if it is directly applied to the transistor.
Therefore, a voltage down-converter is required. The voltage down-converter is mounted within the semiconductor device, and serves to down-convert a high external power supply potential to the level acceptable to the miniaturized transistor in terms of reliability.
FIG. 23
is a circuit diagram showing the structure of a conventional voltage down-converter
524
.
Referring to
FIG. 23
, voltage down-converter
524
includes a reference potential generator
534
for outputting reference potentials VREF, VBGR, and a down-converting portion
536
for receiving reference potentials VREF, VBGR, down-converting an external power supply potential EXTVDD and outputting an internal power supply potential INTVDD. Internal power supply potential INTVDD is supplied to a load circuit
526
. Reference potential generator
534
and down-converting portion
536
have the same structure as that of a reference potential generator
34
E and a down-converting portion
36
described later. Therefore, description thereof will not be given herein. In the figure, a resistor R
2
A has the same resistance value as that of a resistor R
2
.
Down-converting portion
536
is a circuit for receiving an external power supply potential EXTVDD and generating a lower internal power supply potential INTVDD based on a reference potential VREF generated by reference potential generator
534
. Internal power supply potential INTVDD is given by the following expression (1):
INTVDD
=
R5
+
R6
R5
*
VREF
.
(
1
)
Accordingly, internal power supply potential INTVDD varies with variation in reference potential VREF. In order to prevent this, a semiconductor device is designed so that reference potential VREF is less susceptible to the internal power supply potential, process variation, and temperature variation.
FIG. 23
shows a bandgap-type reference potential generator
534
. A bandgap-type reference potential generator is also called a “bandgap voltage reference”, and is commonly used as a reference potential generator causing less variation in reference potential VREF.
Hereinafter, a voltage generated by the bandgap-type reference potential generator will be described. In general, a current flowing through a diode is given by the following expression (2), where Is is a saturation current, q is the amount of charges of electron, k is a Boltzmann's constant, T is an absolute temperature and Vbe is a base-emitter voltage:
I
=
I
s
(
ⅇ
q
V
b
e
k
T
-
1
)
≃
I
s
*
ⅇ
q
V
b
e
k
T
(
∵
Vbe
⪢
kT
q
)
.
(
2
)
From the expression (2)
Vbe
=
kT
q
*
ln
I
Is
.
(
3
)
Accordingly, in
FIG. 23
,
Vbe1
-
Vbe2
=
kT
q
(
ln
I1
Is
-
ln
I2
Is
)
=
kT
q
*
ln
(
n
*
I1
I2
)
.
(
4
)
Provided that V(W12)=V(W13), I1=I2. Therefore,
Vbe1
-
Vbe2
=
kT
q
*
ln
(
n
)
.
(
5
)
Moreover, since Vbe2=VBGR−(R1+R2)I2 and Vbe1=VBGR−R2I1,
R2I1
+
(
R1
+
R2
)
I2
=
kT
q
ln
(
n
)
R1R2
=
kT
q
ln
(
n
)
,
I1
=
I2
=
kT
q
ln
(
n
)
R1
.
(
6
)
From the expression (6),
VBGR
=
R2I1
+
Vbe1
=
Vbe1
+
R2
R1
*
kT
q
*
ln
(
n
)
.
(
7
)
Therefore,
VREF
=
R3
R3
+
R4
VBGR
=
R3
R3
+
R4
(
Vbe1
+
R2
R2
·
kT
q
·
ln
(
n
)
)
.
(
8
)
Note that the expression (5) is obtained on the assumption that V(W12)=V(W13). The reason for this is as follows: since transistors P
1
, P
2
of the same size are used, the same current flows through transistors P
1
, P
2
. In this case, by using transistors N
1
, N
2
of the same size, a differential amplifier
38
E controls the gate of a transistor P
6
so that V(W12)=V(W13).
Potentials VBGR, VREF generated by reference potential generator
534
in
FIG. 23
are thus given by the above expressions (7), (8), respectively.
Reference potential VREF is adjusted by adjusting the resistance value of resistors R
3
, R
4
. The level of internal power supply potential INTVDD is thus adjusted.
Resistors R
1
, R
2
are formed from the same material so as to have the same variation in characteristics and the same temperature dependency. Similarly, resistors R
3
, R
4
are formed from the same material so as to have the same variation in characteristics and the same temperature dependency. Similarly, resistors R
5
, R
6
are formed from the same material so as to have the same variation in characteristics and the same temperature dependency. In the figure, resistors R
2
, R
2
A have the same resistance value and are formed from the same material.
It is known that process variation is a factor that cannot be ignored for a threshold voltage Vth of a MOS (Metal Oxide Semiconductor) transistor. In contrast, as described in “Analog Integrated Circuit Design Technology for VLSI”, Vol. 2, P. R. Gray, R. G. Meyer, Baifukan Co., Ltd, p. 310, Vbe is approximately unique to a material such as silicon and has little variation. However, Vbe has temperature dependency of about −2 mV/° C. Accordingly, ∂VBGR/∂T=0 is achieved by determining the resistance value of resistors R
1
, R
2
so as to satisfy the following expression (9):
R2
R1
=
-
∂
Vbe
∂
T
*
q
k
÷
ln
(
n
)
.
(
9
)
As a result, potential VBGR generated by bandgap-type reference potential generator
534
is less susceptible to power supply voltage, process variation and temperature.
Accordingly, reference potential VREF is also less susceptible to power supply voltage, process variation and temperature.
Thus, internal power supply potential INTVDD can be generated without being significantly affected by power supply voltage, process variation and temperature.
Recently, reduction in power consumption is increasingly required for the semiconductor devices, and therefore reduction in current consumption in the standby period is a prime task in the industry. In the semiconductor devices such as static random access memory (SRAM) and dynamic random access memory (DRAM), the value of a semiconductor device is determined mainly based on how fast the semiconductor device can start operation such as read and write operations after it transitions from standby to active state.
However, the voltage down-converter must drive a huge load circuit. Therefore, quick start operation cannot be implemented if the voltage down-converter is not operated until the semiconductor device transitions to the active state (i.e., if the voltage down-converter is stopped while the semiconductor device is in the standby state for the purpose of power saving).
Accordingly, the voltage down-converter must be operated from the standby state of the semiconductor device. Current consumption of the voltage down-converter thus accounts for a large percentage of a standby current of the semiconductor device. It
Cunningham Terry D.
McDermott Will & Emery LLP
Renesas Technology Corp.
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