Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
1999-11-09
2002-01-22
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C323S273000
Reexamination Certificate
active
06340852
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to voltage generating circuits, and more specifically to a voltage generating circuit which can stably supply internal power supply voltage not exceeding rated voltage for the internal power supply voltage when external power supply voltage higher than the rated voltage is applied.
2. Description of the Background Art
In order to cope with the need for semiconductor devices having larger capacity and operating at higher speed, efforts have been made to reduce the size of elements. To cope with reduction in the breakdown voltage of the elements associated with such miniaturization, the operation power supply voltage has been lowered from the conventional 5V to 3.3V. Thus, some ICs including a semiconductor device are manufactured to have a rated value of 3.3V for the operation-guaranteed voltage, while the others still have the conventional, rated voltage value of 5V.
Under the circumstances, devices with various rated voltages are in the market such as PC card slots installed in PCs or the like and in these IC-installed circuits, the rated voltage can be 3.3V or 5V, or some devices are adapted to operate selectively with any of 3.3V or 5V.
Therefore, when an IC having an operation-guaranteed voltage of 3.3V is installed, a voltage generating circuit which can stably output 3.3V as an output power supply voltage is necessary in order to guarantee the operation of the IC as a board capable of operating with both 5V and 3.3V.
Japanese Patent Laying-Open No. 6-149395 discloses a voltage generating circuit for such an application incorporated in a semiconductor device. (Hereinafter, the disclosed voltage generating circuit will be referred to as “conventional voltage generating circuit”.)
FIG. 12
is a schematic block diagram showing the general configuration of a conventional voltage generating circuit
500
.
Referring to
FIG. 12
, voltage generating circuit
500
receives an external power supply voltage VCE at an external power supply terminal
510
and supplies an internal power supply voltage Vcc to an internal circuit power supply interconnection
590
. The operation power supply voltage is supplied through internal circuit power supply interconnection
590
to an internal circuit
550
. Internal circuit
550
includes a decoder circuit
555
, a sense amplifier circuit
556
and a control circuit
557
.
Voltage generating circuit
500
includes a voltage down-converting circuit
520
to convert external power supply voltage VCE to internal power supply voltage Vcc, a power supply voltage detecting circuit
530
to detect the size of external power supply voltage VCE to send a control signal for controlling a switch circuit
540
, and switch circuit
540
to transmit one of the output of voltage down-converting circuit
520
and external power supply voltage VCE to internal circuit power supply interconnection
590
in response to the control signal.
Voltage generating circuit
500
stably supplies a voltage of 3.3V, a rated value for the internal power supply voltage to internal circuit
550
if external power supply voltage VCE is either 5V or 3.3V.
FIG. 13
is a circuit diagram of the configuration of switch circuit
540
.
Referring to
FIG. 13
, switch circuit
540
includes a P-type MOS transistor Q
31
and an N-type MOS transistor Q
32
forming a transfer gate which connects an external power supply interconnection
570
and internal circuit power supply interconnection
590
in response to an activation of a control signal MO
1
. Switch circuit
540
further includes a P-type MOS transistor Q
33
and an N-type MOS transistor Q
34
forming a transfer gate which connects voltage down-converting circuit
520
and internal circuit power supply interconnection
590
in response to an activation of a control signal M
02
.
Thus, when external power supply voltage VCE is 5V, control signal MO
1
attains an H level (active state) and control signal M
02
attains an L level (inactive state), so that the output of voltage down-converting circuit
520
is transmitted to internal circuit power supply interconnection
590
. Meanwhile, when external power supply voltage VCE is 3.3V, control signal MO
1
attains an L level, and control signal M
02
attains an H level, so that external power supply voltage VCE is directly transmitted to internal circuit power supply interconnection
590
.
FIG. 14
is a circuit diagram of the configuration of a power supply voltage detecting circuit
530
.
Referring to
FIG. 14
, power supply voltage detecting circuit
530
includes P-type MOS transistors Q
21
, Q
22
and an N-type MOS transistor Q
23
connected in series between external power supply voltage interconnection
570
and a ground interconnection
580
. The substrate region of transistor Q
21
is connected to external power supply interconnection
570
. The substrate region of transistor Q
22
, the gate of transistor Q
21
and the source of transistor Q
22
are connected to the drain of transistor Q
21
. The gate and drain of transistor Q
22
are connected to a node Nx. Transistor Q
23
is connected between node Nx and ground interconnection
580
and has a gate connected to ground interconnection
580
.
Power supply voltage detecting circuit
530
further includes a P-type MOS transistor Q
24
and an N-type MOS transistor Q
25
forming an inverter which inverts the voltage level of node Nx for output to an internal node Ny, and a P-type MOS transistor Q
26
and an N-type MOS transistor Q
27
forming an inverter which inverts the voltage level of a node Ny for output to a node Nz.
Transistors Q
24
and Q
25
are connected in series between external power supply interconnection
570
and ground interconnection
580
, and have their gates connected to node Nx. Transistors Q
26
and Q
27
are connected between external power supply interconnection
570
and ground interconnection
580
and have a gate connected to node Ny. The voltage level of control signal MO
1
is equal to the voltage level of node Nz, while the voltage level of control signal MO
2
is equal to the voltage level of node Ny. Control signals MO
1
and MO
2
are transmitted to switch circuit
540
.
In power supply voltage detecting circuit
530
, the voltage level of node Nx changes according to the level of external power supply voltage VCE.
If external power supply voltage VCE≦2·|VTP| (VTP: the threshold voltage of P-type transistors) holds, transistors Q
21
and Q
22
are in an off state, the voltage of node Nx is 0V (ground voltage). At this time, the voltage levels of nodes Ny and Nz are VCE and 0V, respectively by the function of the inverters formed by transistors Q
24
to Q
27
. More specifically, control signal MO
1
attains an L level, while control signal MO
2
attains an H level.
If external power supply voltage VCE≧2·|VTP|+VI (VI: the logical threshold of inverters) holds, the voltage level of node Nx changes from 0V to VCE, the polarities of control signals MO
1
and MO
2
are inverted as the voltage levels of node Ny and Nz change, and control signal MO
1
attains an H level, while control signal MO
2
attains an L level.
Thus, if the threshold voltage VTP of a P-type transistor and the logical threshold VI of an inverter are designed appropriately, voltage generating circuit
500
can select whether to directly supply the external power supply voltage or supply the output of voltage down-converting circuit
520
to the internal circuit depending upon the result of the comparison between external power supply voltage VCE and a prescribed voltage level.
However, in this conventional voltage generating circuit
500
, before external power supply interconnection
570
is activated, in other words before voltage is actually supplied to external power supply interconnection
570
, VCE=0V holds, and therefore control signal MO
1
attains an L level, so that external power supply interconnection
570
and internal circuit power supply interconnection
590
are connected by switch
Ballato Josie
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Rios Roberto
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