Power supply voltage step-down circuit, delay circuit, and semiconductor device having the delay circuit

1. A power supply voltage step-down circuit comprising:

a level generating circuit which adds an offset voltage to a manufacturing variation dependent voltage and outputs a resulting variable reference voltage;

an m-time voltage generating circuit which multiplies the reference voltage by m, where m is a positive number, and outputs the resulting multiplied voltage.

2. The power supply voltage step-down circuit as claimed in claim 1 , wherein the level generating circuit comprises a differential amplifier and an output stage, the output stage comprising a transistor supplied with an output of the differential amplifier, a plurality of transistors each of which is diode-connected, and a constant current source, wherein the transistors, the diode-connected transistors, and the constant current source are connected in sequence between a power supply voltage and an internal power supply voltage, the differential amplifier being supplied with the offset voltage and a potential of a connection point of the constant current source and the diode-connected transistors.

3. The power supply voltage step-down circuit as claimed in claim 1 , wherein the m-time voltage generating circuit comprises a differential amplifier and an output stage, the output stage comprising a transistor supplied with an output of the differential amplifier and resistors, the differential amplifier being supplied with an output of the level generating circuit and a potential of a split node of the resistors.

4. A power supply voltage step-down circuit comprising a level generating circuit for generating a reference voltage obtained by adding an offset voltage and a manufacturing variation dependent voltage and an m-time voltage generating circuit for producing a voltage obtained by multiplying the reference voltage by m, where m is a positive number,

wherein the manufacturing variation dependent voltage is equal to n times a threshold voltage of a MOS transistor, where n is a positive integer.

5. A delay circuit comprising a plurality of stages of inverter circuits in each of which a delay time is dominated by a PMOS or an NMOS transistor, the inverter circuits being supplied with, as a variable power supply voltage, a voltage obtained by adding an offset voltage and a manufacturing variation dependent voltage to produce a variable reference voltage and multiplying the variable reference voltage by m, where m is a positive number.

6. A delay circuit comprising a plurality of stages of inverter circuits in each of which a delay time is dominated by a PMOS or an NMOS transistor, the inverter circuits being supplied with, as a power supply voltage, variable output voltage from a power supply voltage step-down circuit comprising a level generating circuit for generating a variable reference voltage obtained by adding an offset voltage and a manufacturing variation dependent voltage and a m-time voltage generating circuit for producing a variable voltage obtained by multiplying the variable reference voltage by m, where m is a positive number.

7. The delay circuit as claimed in claim 6 , wherein the power supply voltage step-down circuit determines the offset voltage and the value of m from a power supply voltage value at which the delay time is substantially same in a manufacturing variation best condition and a manufacturing variation worst condition, the power supply voltage step-down circuit producing a high power supply voltage in a condition that the delay time of the delay circuit is large and a lower power supply voltage in a condition that the delay time of the delay circuit is small.

8. A delay circuit comprising a plurality of stages of inverter circuits in each of which a delay time is dominated by a PMOS or an NMOS transistor, the inverter circuits being supplied with, as a power supply voltage, an output voltage from a power supply voltage step-down circuit comprising a level generating circuit for generating a reference voltage obtained by adding an offset voltage and a manufacturing variation dependent voltage and an m-time voltage generating circuit for producing a voltage obtained by multiplying the reference voltage by m, where m is a positive number,

wherein the manufacturing variation dependent voltage is equal to n times a threshold voltage of the MOS transistor dominating the delay time of the delay circuit, where n is a positive integer.

9. A semiconductor device comprising a delay circuit and a power supply voltage step-down circuit, the delay circuit comprising a plurality of stages of inverter circuits in each of which a delay time is dominated by a PMOS or an NMOS transistor, the power supply voltage step-down circuit comprising a level generating circuit for generating a variable reference voltage obtained by adding an offset voltage and a manufacturing variation dependent voltage and a m-time voltage generating circuit for producing a variable voltage obtained by multiplying the reference voltage by m, where m is a positive number, the delay circuit being supplied with, as a power supply voltage, a variable output voltage of the power supply voltage step-down circuit.

10. The semiconductor device as claimed in claim 9 , wherein a sense amplifier activation signal is delayed by the delay circuit.