MLX90320_12 Datasheet, PDF (13/33 Pages) Melexis Microelectronic Systems – Automotive sensor interface

6.4 The sensor signal chain.
MLX90320
Automotive sensor interface
Figure 4 The sensor signal chain
The input of the sensor signal chain is a differential voltage INP-INM. The differential inputs can be inverted by
setting the IINV bit (EEPROM address 7). This is done by a 180º phase shift of the chopping signal. This allows
calibrating a decreasing output characteristic instead of an increasing one as shows Figure 2.
A dual input dual output 1 bit gain programmable amplifier (Gdido) is the first amplifier stage of the sensor signal
chain. The use of noise and offset reduction techniques like chopping and sample and hold makes the
contribution of the on-chip noise, offset and offset drift negligible compared to the same imperfections from the
external sensor. A dual input single output 1 bit programmable gain amplifier (Gdts) and a 1 bit programmable
gain charge summing amplifier (Gcs) completes the programmable coarse gain of the sensor signal chain.
Thanks to the wide programmable coarse gain range, the MLX90320 can accommodate wide sensor output
spans.
A coarse and fine sensor offset compensation is done at the inputs of the dual to single amplifier (Gdts). A fine
gain DAC allows calibrating accurately the output span. A wide range of sensor offsets can be compensated with
the coarse offset calibration while the desired output offset can be achieved accurately with the fine offset
calibration. The fine gain and offset calibration allows compensating a second order temperature drift of the
sensor sensitivity and offset. An external capacitor connected to the FLT pin sets the bandwidth of the
MLX90320.
The global equations of the sensor signal chain are given below:
POS _OUT
− NEG_OUT
=
^GDIDO
 ^GDIDO
×
×
(INP − INM ),if
(INM − INP),if
_ IINV
_ IINV
=0
=1
AGND = 0.699 ×V_DD
( ) ( ) Dts_OUT = −G_DTS × POS_OUT − NEG_OUT
+ ^GDTS
3
×
FN _OFF
− CS_OFF
+ AGND
CS_OUT = G_CS × (Dts_OUT − AGND)+ AGND
Gn_IN = FN_GAIN (× CS_OUT − AGND)+ AGND
3901090320
Rev 007
Page 13 of 33
Data Sheet
Feb/12