Semiconductor device with A/D converter

1. A semiconductor device comprising:

a reference voltage generating section configured to generate a first reference voltage and a second reference voltage based on a voltage supplied from an external power supply; and

an AD (analog/digital) conversion circuit operating based on said first reference voltage to generate an AD conversion signal corresponding to an output signal supplied from an external device,

wherein said second reference voltage is supplied to said external device, and

a ratio of said first reference voltage and said second reference voltage is kept to a constant value regardless of a temperature of said semiconductor device.

2. The semiconductor device according to claim 1 , wherein said reference voltage generating section comprises:

an internal reference voltage generating circuit configured to generate said first reference voltage based on the voltage supplied from said external power supply; and

an external reference voltage generating circuit configured to generate said second reference voltage from said first reference voltage such that the ratio is kept.

3. The semiconductor device according to claim 1 , further comprising an amplifying circuit provided between said external device and said AD conversion section and configured to amplify the output signal supplied from said external device to output an amplification signal,

wherein said AD conversion circuit carries out the AD conversion to said amplification signal based on said second reference voltage to generate the AD conversion signal.

4. The semiconductor device according to claim 3 , wherein, said reference voltage generating section further generates a third reference voltage from said first reference voltage, and

said amplifying circuit comprises:

an operational amplifier; and

a bias control circuit configured to apply a bias voltage to an input terminal of said operational amplifier based on said third reference voltage in response to a control signal.

5. The semiconductor device according to claim 1 , wherein said reference voltage generating section comprises two voltage follower circuits configured to supply said first and second reference voltages to said AD conversion circuit and said external device, respectively.

6. The semiconductor device according to claim 1 , further comprising:

a microcomputer configured to temporarily store the AD conversion signal and output the AD conversion signal as a digital data signal.

7. A data communication apparatus comprising:

a sensor; and

a semiconductor device configured to generate a digital data signal based on an output signal which is outputted from said sensor,

wherein said semiconductor device comprises:

an amplifying circuit configured to amplify the output signal outputted from said sensor to generate an amplification signal;

an AD (analog/digital) conversion circuit configured to carry out AD conversion to the amplification signal from said amplifying circuit to generate an AD conversion signal;

a microcomputer configured to generate said digital data signal based on the AD conversion signal; and

a reference voltage generating section configured to generate first and second reference voltages from a voltage supplied from a power supply, and to supply said first and second reference voltages to said AD conversion circuit and said sensor, and a ratio of said first reference voltage and said second reference voltage is kept to be constant regardless of a temperature of said semiconductor device.

8. The data communication apparatus according to claim 7 , wherein said reference voltage generating section comprises:

an internal reference voltage generating circuit configured to generate said first reference voltage based on the voltage supplied from said power supply; and

an external reference voltage generating circuit configured to generate said second reference voltage from said first reference voltage such that the ratio is kept.

9. The data communication apparatus according to claim 7 , wherein said reference voltage generating section further generates a third reference voltage from said first reference voltage, and

said amplifying circuit comprises:

an operational amplifier; and

a bias control circuit configured to apply a bias voltage to an input terminal of said operational amplifier based on said third reference voltage in response to a control signal.

10. A vehicle having tires, comprising:

a data communication unit provided for at least one of the tires; and

a control unit configured to receive a pneumatic pressure data transmitted from said data communication unit,

wherein said data communication unit comprises:

a pressure sensor configured to detect pneumatic pressure of a tire to generate a sensor signal;

a semiconductor device configured to generate the pneumatic pressure data based on the sensor signal outputted from said pressure sensor,

wherein said semiconductor device comprises:

an amplifying circuit configured to amplify the sensor signal outputted from said pressure sensor to generate an amplification signal;

an AD (analog/digital) conversion circuit configured to convert the amplification signal from said amplifying circuit into an AD conversion signal;

a microcomputer configured to generate the pneumatic pressure data based on the A/D conversion signal and transmit the pneumatic pressure data to said control unit; and

a reference voltage generating circuit connected with said AD conversion circuit and configured to generate a basic reference voltage for a reference voltage, a reference voltage generating section configured to generate first and second reference voltages from a voltage supplied from a power supply, and to supply said first and second reference voltages to said AD conversion circuit and said pressure sensor, and a ratio of said first reference voltage and said second reference voltage is kept to be constant regardless of a temperature of said semiconductor device.

11. The vehicle according to claim 10 , wherein said reference voltage generating section comprises:

an internal reference voltage generating circuit configured to generate said first reference voltage based on the voltage supplied from said power supply; and

an external reference voltage generating circuit configured to generate said second reference voltage from said first reference voltage such that the ratio is kept.

12. The vehicle according to claim 10 , wherein said reference voltage generating section further generates a third reference voltage from said first reference voltage, and

said amplifying circuit comprises:

an operational amplifier; and

a bias control circuit configured to apply a bias voltage to an input terminal of said operational amplifier based on said third reference voltage in response to a control signal.