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Datasheet A2TPMI
General Description
THERMOPILE SENSOR
The signal voltage, generated by the infrared radiation-sensitive thermopile sensor, is preamplified by a
programmable choppered amplifier with 8 bit resolution.
Due to the principle of thermopile temperature measurements, the thermopile voltage can be positive or
negative depending if the object temperature is higher or lower than the ambient temperature of the
A2TPMI. In order to allow signal processing of negative voltages with a single supply system, all internal
signals are related to an internal voltage reference (Vref) of nominal 1.225 V, which serves as a virtual
analog ground.
For offset voltage trimming of the thermopile amplification path, the preamplifier is followed by a
programmable trimming stage generating an offset voltage with a resolution of 8 bit.
The thermopile voltage shows a non-linear output characteristic versus the object temperature.
AMBIENT TEMPERATURE SENSOR
The temperature of the A2TPMI, respectively the thermopile sensor, is detected by an integrated tem-
perature sensor. This signal will be amplified and signal processed in order to match the reverse char-
acteristics of the amplified thermopile curve, to realize an optimum of ambient temperature compensa-
tion after adding the two signals. The characteristics of the temperature sensor signal is adjustable.
This adjustment is part of the ASIC production process and will be provided by PerkinElmer. Thus the
characteristics of the A2TPMI ambient temperature signal VTamb is always provided fully calibrated.
AMBIENT TEMPERATURE COMPENSATION
The thermopile sensor converts the temperature radiation of an object surface to an electrical signal by
means of thermocouples (Seebeck effect). The sensor output voltage is caused by the temperature
difference between radiation heated (hot) junctions and cold junctions with a good thermal contact to the
housing.
In order to deliver an output signal which is only dependent on the object temperature, any change of
housing (ambient) temperature has to lead to an appropriate output signal correction.
For temperature compensation, the amplified thermopile- and temperature reference signals (VTambint)
are added in an adding amplifier stage. The amplification is adjustable in a wide range according to
application / customer requirements.
The ambient temperature compensated and amplified signal is supplied to the output VTobj. The tem-
perature reference signal or alternatively the bandgap reference voltage is available on a second output
pin VTamb. Both outputs are short circuit stable .
A2TPMI Datasheet Rev4
Page 9 of 21
Rev. Oct 2003
PERKINELMER [ PERKINELMER OPTOELECTRONICS ]
