Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
2001-03-20
2002-11-26
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
Reexamination Certificate
active
06487100
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor integrated circuit device and a contactless electronic device and more particularly to a technique utilized effectively in a stable power supply circuit of a contactless IC card and semiconductor integrated circuit devices mounted on the contactless IC card.
In recent years, a so-called IC card on which semiconductor integrated circuit devices are mounted has come into wide use. The IC card attains exchange of information between a reader/writer and the semiconductor integrated circuit devices and realizes various functions equal to those performed by a magnetic card at present. In a contactless IC card having no external electrode through which a signal and a voltage are supplied to the IC card, an antenna mounted in the IC card receives electromagnetic wave supplied from the reader/writer and a voltage generated across the antenna is rectified to produce an internal voltage required for operation of an inner circuit including semiconductor integrated circuit devices mounted on the IC card. In this case, when excessive electric power is supplied to the inner circuit from the reader/writer so that a power supply voltage higher than a breakdown voltage of the devices constituting the inner circuit is supplied to the inner circuit, the devices are broken. In order to prevent such breakdown, it is necessary to monitor a power supply voltage level and control to prevent a power supply voltage higher than the breakdown voltage from being supplied to the inner circuit.
SUMMARY OF THE INVENTION
The inventors of the present invention have studied a power supply circuit as shown in
FIG. 17
on the basis of the technique disclosed in JP-A-11-353041 published on Dec. 24, 1999. In this circuit, an anode terminal of a diode D
01
is connected to an input terminal IN
1
and a cathode terminal of the diode D
01
is connected to an output terminal OUT
1
. An anode terminal of a diode D
02
is connected to a junction N
04
and a cathode terminal thereof is connected to an input terminal IN
2
. A condenser C
01
is connected between the output terminal OUT
1
and the junction N
04
to constitute a half-wave rectifier circuit.
The following circuit is provided in order to stabilize an internal voltage. A source terminal of a P-channel MOSFET (hereinafter referred to as PMOS transistor) M
01
is connected to an output terminal OUT
2
and a drain terminal thereof is connected to the junction N
04
. Resistors R
01
and R
02
constituting a voltage divider is connected in series to each other between the output terminals OUT
1
and OUT
2
. A divided voltage generated at a junction N
01
of the resistors R
01
and R
02
is supplied to an inverting input (−) of a voltage comparator circuit (operational amplifier circuit) A
01
. A reference voltage VREF is supplied to a non-inverting input (+) of the voltage comparator circuit A
01
and a comparison output voltage of the comparator circuit is applied to a gate of the PMOS transistor M
01
.
In the power supply circuit shown in
FIG. 17
, an input signal applied between the input terminals IN
1
and IN
2
is rectified by the half-wave rectifier circuit and is smoothed by the condenser C
01
. The smoothed voltage is obtained as a voltage difference V
12
between the output terminal OUT
1
and the junction N
04
. The smoothed voltage V
12
is given by
V
12
=VIN−VF
1
−VF
2
(equation 1)
where VIN is an amplitude of an input voltage applied between the input terminals IN
1
and IN
2
, VF
1
a forward voltage of the diode D
01
, and VF
2
a forward voltage of the diode D
02
.
Thus, when the input voltage VIN is increased, the voltage difference V
12
is also increased. Accordingly, when power supply terminals of the inner circuit are connected to the output terminal OUT
1
and the junction N
04
so that the voltage difference V
12
is directly supplied thereto as a power supply voltage, the voltage difference V
12
sometimes exceeds a breakdown voltage of the devices constituting the inner circuit to thereby break the devices. In order to prevent an excessive voltage exceeding the breakdown voltage from being applied to the devices constituting the inner circuit, there is provided a voltage control circuit including the PMOS transistor M
01
and the voltage comparator circuit A
01
.
In the voltage comparator circuit, when a voltage divided by the resistors R
01
and R
02
connected between the output terminals OUT
1
and OUT
2
is higher than the reference voltage VREF (the absolute value of the divided voltage is lower than the absolute value of the reference voltage), the output voltage of the voltage comparator circuit A
01
is reduced, so that the voltage produced by the half-wave rectifier circuit, that is, the voltage across the condenser C
01
is reduced by a voltage (threshold voltage) between the gate and the source of the PMOS transistor to be outputted. On the contrary, when the divided voltage is lower than the reference voltage VREF (the absolute value of the divided voltage is higher than the absolute value of the reference voltage), the output voltage of the voltage comparator circuit A
01
is higher than the voltage at the input terminal IN
2
, so that the gate voltage of the PMOS transistor M
01
is limited to a fixed voltage. Accordingly, the power supply voltage of the inner circuit supplied through the output terminals OUT
1
and OUT
2
is limited to a fixed voltage so as to make the divided voltage equal to the reference voltage VREF. Thus, the output voltage VOUT obtained from the output terminals OUT
1
and OUT
2
is stabilized to satisfy the equation (2).
VOUT=VREF
×(
R
01
+R
02)/
R
01 (equation 2)
In the above circuit operation, by adjusting a resistance ratio of the resistors R
01
and R
02
, the power supply voltage which does not exceed the breakdown voltage of the devices in the inner circuit can be supplied to the inner circuit. However, this operation is attained when the following equation (3) is satisfied among the voltage difference V
12
, the output voltage VOUT and the voltage Vgs
1
between the gate and the source of the PMOS transistor M
01
.
V
12>
VOUT+Vgs
1 (equation 3)
When the input voltage VIN which does not satisfy the equation (3) is inputted, the output voltage is as shown by the following equation (4) and is dependent on the input voltage.
VOUT=V
12−
Vgs
1 (equation 4)
Accordingly, when a sufficiently large input voltage VIN is not supplied, a ratio of the voltage Vgs
1
between the gate and the source to the voltage difference V
12
is increased, so that a sufficiently large output voltage VOUT cannot be obtained. The MOS transistor M
01
is necessarily required to have a higher breakdown voltage since a relatively larger voltage is applied in accordance with the input voltage VIN, and the threshold voltage Vgs
1
of the MOS transistor M
01
is higher than that of MOSFETs in the inner circuit since a relatively larger current supplied to the inner circuit flows through the MOS transistor M
01
. For example, the threshold voltage of the MOS transistors in the inner circuit can be reduced to about 0.6 volts by the miniaturization of the devices, while the threshold voltage of the MOS transistor M
0
is required to consider about 1.5 volts.
As described above, when a voltage loss of the voltage control circuit is increased, a minimum input voltage for normally operating the inner circuit is increased, so that, for example, in the contactless IC card, deterioration of characteristics thereof such as reduction of a communication distance occurs. It is necessary to reduce a voltage loss in the power supply circuit as small as possible so as to prevent such characteristic deterioration. However, in a conventional series regulator in which means for stabilizing the power supply voltage is connected to an output side of means for rectifying and smoothing a received electromagnetic wave, since a voltage loss in means for stabiliz
Kamei Keiji
Kinota Hajime
Watanabe Kazuki
Yamamoto Norihisa
Yoshino Ryouzou
Antonelli Terry Stout & Kraus LLP
Hitach, Ltd.
Riley Shawn
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