SM5812 Datasheet, PDF (2/4 Pages) List of Unclassifed Manufacturers – Amplified Pressure Sensor

SM5812/SM5852
THEORY OF OPERATION
The operation of the signal processor is
depicted in the block diagram below. The
external pressure sensor is a piezoresistive
bridge. This transduces the applied pressure
into an electronic signal, which is then inputted
into the integrating amplifier of the ASIC.
During the amplification step an offset
correction factor is added in order to allow
maximum gain for a given pressure while
minimizing the offset error.
The signal is then passed to an 11-bit analog
to digital converter (ADC). The ADC samples
the signal multiple times and uses the sum of
those samples as a 13-bit word.
A digital signal processor (DSP) is then used
to correct and calibrate the pressure signal.
The DSP provides multi-order correction of
both pressure and temperature non-linearity
through the use of factory-programmed
coefficients. A combined total of twenty
coefficients are available for correcting
pressure and temperature non-linearity. The
unique coefficients are determined during a
calibration process performed at the factory.
Factory calibration is the last step performed
which means the effect of the package on
the pressure signal will also be taken into
account. This provides a great advantage
over conventional laser-trimming
approaches.
The DSP outputs a corrected digital word,
which travels to a 12-bit digital to analog
converter (DAC) to provide a calibrated
analog output. In addition to the analog
output, the corrected pressure signal is
accessible through an I²C digital interface.
See SMI application note AN05-001 for a
detailed description of how to read out the
digital corrected pressure signal using the
I2C bus interface.
+ 5 VDC
External
Piezoresistive
Bridge
Ground
SMI Multi-Order Pressure and
Temperature Correction ASIC
Band-gap
V_Temp
Switched
Capacitor
Integrateing
Amplifier
+ 5 VDC
MUX
11-bit ADC
DSP
(multi-order
correction of
pressure and
temperature
non-
linearities)
12-bit
Sigma-
Delta DAC
Power-On
Reset
Analog
Timing
Control
2 MHz
Oscillator
EEPROM
Array
Digital Timing
and Control
Management
Ground
Output
Buffer
Analog
Output
I²C Digital
Interface
SDA
SCL
Analog Component
Digital Component
Rev 1.4 6_05
 2005 SMI
Silicon Microstructures, Inc. ♦ 1701 McCarthy Blvd. ♦ Milpitas, CA 95035 ♦ USA
Tel: [phone] ♦ Fax: [phone] ♦ [e-mail] ♦ www.si-micro.com