Board Mount Pressure Sensor

AMS 6915 SERIES

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Datasheet AMS 6915

– Rev. 2.0

5/13

FUNCTIONAL DESCRIPTION

The pressure sensors in the AMS 6915 series combine a membrane based piezoresistive silicon sensing el-

ement with a modern mixed-signal CMOS ASIC for signal-conditioning on a ceramic substrate. This enables

high precision measurements and excellent drift and long-term stability.

The functional principle of the AMS 6915 sensors is explained using Figure 1.

The physical pressure is measured at AMS 6915

’s piezoresistive pressure sensing element, where the

pressure is converted into a differential voltage signal, which is almost proportional to the pressure. This

differential voltage signal is corrected and conditioned by the ASIC in multiple steps.

First, the differential voltage signal from the sensing element is pre-

amplified by the ASIC’s amplifier stage

and transmitted to the A/D converter stage (ADC) by the multiplexer stage. The ADC stage converts this

voltage signal into digital values with a resolution of 14 bits. The digitized signal is corrected and calibrated in

the subsequent ASIC microcontroller block.

During AMS 6915’s factory calibration, sensor-specific correction coefficients are determined and stored in

the respective

sensor’s EEPROM. This permits sensor-specific calibration and correction (i.e. temperature

compensation and linearization) of the digitized pressure signal. The temperature signal required for

temperature compensation is generated at the ASIC’s temperature reference block and is transmitted by the

multiplexer stage to the ADC stage, where it is digitized. The ASIC’s microcontroller block runs a cyclic

program, which continuously calculates the current standardized and corrected digital pressure value using

the current digitized pressure and temperature values as well as the stored correction coefficients. In

addition, a standardized current digital temperature value is calculated. These calculated and corrected

digital values (14 bit pressure value and 11 bit temperature value) are written to the ASIC

’s output registers

and continuously updated (typically every 0.5 ms).

The readout of the standardized digital output values for pressure and temperature from the output registers

is done via the sensor’s I²C interface at PIN3 (SDA) and PIN4 (SCL). The AMS 6915’s digital output values

(for pressure and temperature) are not ratiometric to the supply voltage.

Figure 1: Functional principle