ZMD31020
Sensor Signal Conditioner
Datasheet
The digital signal correction takes place in the calibration micro-controller (CMC). It is based on a special
correction formula located in the ROM and on a set of sensor-specific calibration parameters stored in the
EEPROM. The resulting corrected sensor signal is output via the I2C-interface (with 12 bits resolution) , or, after
conversion by the DAC, as analog voltage (with 11 bits resolution) at the buffer amplifier (BAMP). The
programming of the configuration data and of the calibration parameters into the EEPROM (during the
calibration procedure) is also realized via the I2C interface.
2.2 Configuration Word
Many of the following sections, describing each block of ZMD31020 in detail, will refer to configuration bits, part
of the configuration word stored under address &H09 of the parameter EEPROM. These bits are settings for a
number of on-chip device functions and select specific functional or parametrical behaviour.
The contents of the parameter EEPROM are determined and calculated, written and stored under PC-control
during the calibration procedure. Hence the configuration bits are coded and non-volatile stored once calibration
of a ZMD31020 device / sensor pair has taken place, and will remain unchanged during regular sensing
operation, unless re-calibration is performed
15
-
14
-
13
-
12
-
11
-
10
-
9
-
8
-
7
-
6
CH
5
TS
4
BP
3
G1
2
G0
1
O1 O0
0
Configuration word, stored under address &H09 of the parameter EEPROM
Only 7 bits of the configuration word are relevant settings as follows:
Bit 0, Bit 1
Bit 2, Bit 3
Bit 4
Bit 5
Bit 6
O0, O1: select ADC’s offset compensation
G0, G1: select PGA’s gain
BP: cross-switches differential sensor inputs VBP and VBN
TS: selects on-chip vs. off-chip temperature sensor
CH: enables PGA’s chopper-stabilization
The possible options of these settings are shown in table form in the following paragraphs.
2.3 Differential Sensor
ZMD31020 has been specifically designed for ratiometric differential sensors, e.g. Wheatstone bridge type
sensors. A ratiometric sensor typically generates a differential output signal proportional to the supply voltage
applied to it. The sensor is supplied from VDDB1 or VDDB2 (whichever pin/pad is more favourable layoutwise)
at the + side and tied to VSSB at the – side. The sensor's differential output signal is routed to VBP and VBN.
Sensor and signal conditioner ZMD31020 have the same supply (see block schematic in section 2.1), hence the
differential input voltage seen by ZMD31020 is ratiometric to it’s supply voltage.
2.4 Temperature Sensing
The characteristic of a sensor element tends to change with temperature. To compensate for this, ZMD31020 is
equipped to measure temperature by an external diode or by an on-chip pn-junction. TS – configuration bit 5 –
will select the desired sensor option as follows:
TS
Temperature sensing diode
0
1
off chip
on chip
Copyright © 2004, ZMD AG, Rev. 1.6, 2005-05-19
5/19
All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior
written consent of the copyright owner. The Information furnished in this publication is preliminary and subject to changes without notice.
ZMD [ Zentrum Mikroelektronik Dresden AG ]
