MLX90614_15 Datasheet, PDF (10/51 Pages) Melexis Microelectronic Systems – Single and Dual Zone Infra Red Thermometer in TO-39

8 Detailed description
8.1 Block diagram
MLX90614 family
Single and Dual Zone
Infra Red Thermometer in TO-39
81101
OPA
ADC
DSP
PWM
t°
STATE MACHINE
90302
Voltage
Regulator
Figure 3: Block diagram
8.2 Signal processing principle
The operation of the MLX90614 is controlled by an internal state machine, which controls the
measurements and calculations of the object and ambient temperatures and does the post-processing of the
temperatures to output them through the PWM output or the SMBus compatible interface.
The ASSP supports 2 IR sensors (second one not implemented in the MLX90614xAx).The output of the
IR sensors is amplified by a low noise low offset chopper amplifier with programmable gain, converted by a
Sigma Delta modulator to a single bit stream and fed to a powerful DSP for further processing. The signal is
treated by programmable (by means of EEPROM contend) FIR and IIR low pass filters for further reduction of
the band width of the input signal to achieve the desired noise performance and refresh rate. The output of the
IIR filter is the measurement result and is available in the internal RAM. 3 different cells are available: One for
the on-board temperature sensor and 2 for the IR sensors.
Based on results of the above measurements, the corresponding ambient temperature Ta and object
temperatures To are calculated. Both calculated temperatures have a resolution of 0.01˚C. The data for Ta and
To can be read in two ways: Reading RAM cells dedicated for this purpose via the 2-wire interface (0.02°C
resolution, fixed ranges), or through the PWM digital output (10 bit resolution, configurable range).
In the last step of the measurement cycle, the measured Ta and To are rescaled to the desired output
resolution of the PWM) and the recalculated data is loaded in the registers of the PWM state machine, which
creates a constant frequency with a duty cycle representing the measured data.
3901090614
Rev 009
Page 10 of 52
Data Sheet
June 29, 2015