Copyright © 2004, ZMD AG, Rev. 1.6, 2005-05-19

5/19

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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 I

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 I

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

5

4

3

2

1

0

-

-

-

-

-

-

-

-

-

CH

TS

BP

G1

G0

O1

O0

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

O0, O1: select ADC’s offset compensation

Bit 2, Bit 3

G0, G1: select PGA’s gain

Bit 4

BP: cross-switches differential sensor inputs VBP and VBN

Bit 5

TS: selects on-chip vs. off-chip temperature sensor

Bit 6

CH: enables PGA’s chopper-stabilization

The possible options of these settings are shown in table form in the following paragraphs.

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.

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

off chip

1

on chip

2.2 Configuration Word

2.3

Differential Sensor

2.4

Temperature Sensing