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.
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
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.
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.
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
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.
SMI Multi-Order Pressure and
+ 5 VDC
Temperature Correction ASIC
+ 5 VDC
Band-gap
External
Piezoresistive
V
Temp
Bridge
DSP
(multi-order
correction of
pressure and
temperature
non-
12-bit
Sigma-
Switched
MUX
11-bit ADC
Capacitor
Delta DAC
Ground
Integrateing
Amplifier
linearities)
Analog
Output
Buffer
Analog
Output
Power-On
Timing
Reset
EEPROM
Array
Control
Digital Timing
and Control
Management
2
SDA
SCL
2 MHz
I C Digital
Oscillator
Interface
Analog Component
Digital Component
Ground
Rev 1.4 6_05
2005 SMI
Silicon Microstructures, Inc. ♦ 1701 McCarthy Blvd. ♦ Milpitas, CA 95035 ♦ USA
Tel: 408-577-0100 ♦ Fax: 408-577-0123 ♦ Sales@si-micro.com ♦ www.si-micro.com