MLX90615

Infra Red Thermometer

3901090615

Page 8 of 30

Data Sheet

Rev 001

28/Aug/2008

8 Detailed description

8.1 Block diagram

Figure 3: block diagram

8.2 Signal processing principle

A DSP embedded in the MLX90615 controls the measurements, calculates object and ambient temperatures

and does the post-processing of the temperatures to output them through SMBus compatible interface or

PWM (whichever activated).

The output of the IR sensor is amplified by a low noise, low offset chopper amplifier with programmable gain,

then converted by a Sigma Delta modulator to a single bit stream and fed to the DSP for further processing.

The signal passes a FIR low pass filter. The output of the FIR filter is the measurement result and is available

in the internal RAM. Based on results of the above measurements, the corresponding ambient temperature

An additional IIR LPF is programmable in EEPROM and allows customization of the thermometer output in

order to trade-off noise versus measurement speed . The IIR filter can also limit effect of spurious objects that

may appear in the FOV in some applications.

The PWM output can be enabled in EEPROM as the POR default. Linearized temperatures (To or Ta,

selectable in EEPROM) are available through the free-running PWM output.

8.3 Block description

8.3.1 Amplifier

A low noise low offset amplifier with programmable gain is implemented for amplification of the IR sensor

voltage. With a carefully designed input modulator and balanced input impedance, an offset as low as 0.5

µV

is achieved.

IR sensor

OPA

ADC

FIR/IIR

filters

SMBus /

PWM

DSP

t°

Voltage

Reference

MLX90325

MLX90615