The present invention relates to a semiconductor integrated circuit having a built-in regulator that steps down an external power supply voltage and supplies it to an internal circuit and, more particularly, to a regulator built-in semiconductor integrated circuit which can be used in both a low-voltage/low-consumption current mode and a high-voltage/high-speed operation mode.
Conventionally, semiconductor integrated circuits having equivalent functions are provided as different chips having different design specifications if they have different conditions for use, e.g., different current consumption and a different operation speed. For example, a semiconductor integrated circuit which has a low operation speed but operates with a low current consumption has a built-in regulator which steps down an external power supply voltage and supplies it to an internal circuit. In contrast to this, in a semiconductor integrated circuit which is designed to achieve a high-speed operation, its internal circuit is driven by a voltage substantially equal to the external power supply voltage, so that it operates at a high speed.
If these semiconductor integrated circuits have a common function, they often have a common internal circuit that achieves a specific function as the semiconductor integrated circuit. In this case, one semiconductor integrated circuit can be desirably used in different modes under different conditions, i.e., different current consumptions and different clock frequencies.
More specifically, if one semiconductor integrated circuit can be used in both the low-voltage/low-consumption current mode and the high-voltage/high-speed operation mode, semiconductor integrated circuits that can be used in different conditions can be manufactured with a common mask. This is preferable in terms of the manufacturing process and manufacturing cost as well. Even if the use conditions differ, since a common internal circuit is used, common software that operates the semiconductor integrated circuit can be used.
FIG. 3 shows the arrangement of a conventional regulator built-in semiconductor integrated circuit. Referring to FIG. 3, a semiconductor integrated circuit 3 has an internal circuit 34 for receiving data I0 to Ip and outputting data O0 to Oq, and a regulator 32 for supplying power to the internal circuit 34. The regulator 32 is built in the semiconductor integrated circuit 3, and steps down an external power supply voltage VDDM, e.g., 5 V, which is supplied to an external power supply connection terminal 31, to 2.8 V and supplies the stepped-down voltage to the internal circuit 34 through an internal power supply wiring 33. This decreases current consumption.
In this arrangement, the semiconductor integrated circuit 3 operates with a 6-MHz clock frequency and decreases power consumption of the internal circuit 34. A terminal 35 is a connection terminal to which a capacitance (capacitor) 36 is connected to stabilize the output voltage of the regulator 32.
FIG. 4 shows the arrangement of the regulator 32 shown in FIG. 3. Referring to FIG. 4, the regulator 32 is constituted by a reference voltage generating circuit 321, a comparator 322, an output control transistor 323, and an output resistor 324. The reference voltage generating circuit 321 generates a reference voltage. The comparator 322 compares the reference voltage with the output voltage of the regulator 32 and outputs a control signal corresponding to a difference between them. The output control transistor 323 controls the output of the regulator 32 based on the control signal output from the comparator 322. The output resistor 324 is connected in series with the output control transistor 323.
In the regulator 32 having the above arrangement, the comparator 322 compares the output voltage with the reference voltage. A difference signal between the output voltage and reference voltage drives the output control transistor 323 to supply a predetermined voltage to the internal circuit 34 through the internal power supply wiring 33. An external voltage is supplied t o the reference voltage generating circuit 321 and comparator 322 through the external power supply connection terminal 31.
In the conventional semiconductor integrated circuit 3 described above, however, since only the voltage which is stepped down by the regulator 32 is supplied to the internal circuit 34 through the internal power supply wiring 33, an external power supply voltage cannot be supplied to the internal circuit 34. Even when the internal circuit 34 can be operated at a high speed with a 12-MHz clock frequency by supplying, e.g., an external power supply voltage 5 V, to it, the semiconductor integrated circuit 3 having the built-in regulator 32 cannot be used in an application that requires a high-speed operation with a higher clock frequency.
This also applies to a case wherein the output voltage of the regulator 32 is variable and the external power supply voltage is to be supplied from the external power supply connection terminal 31 through the regulator 32. More specifically, since a voltage drop occurs in the output control transistor 323, the external power supply voltage of 5 V cannot be directly supplied to the internal circuit 34.
When the external power supply voltage is to be directly supplied from the external power supply connection terminal 31 to the internal circuit 34, a switching transistor must be arranged on the line extending from the external power supply connection terminal 31 to the internal power supply wiring 33. In this case, a power capacity W of the switching transistor must be sufficiently large so that the switching transistor has a current supply ability that can cope with a change in load. Then, a large layout area is needed, leading to a large chip size.