MLX90614 family

Single and Dual Zone

Infra Red Thermometer in TO-39

8 Detailed description

8.1 Block diagram

81101

OPA

ADC

DSP

PWM

STATE MACHINE

t°

Voltage

Regulator

90302

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 (on chip PTAT or PTC) 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

Page 10 of 40

Data Sheet

Rev 003

03/Oct/2007