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

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ZMD31020

Sensor Signal Conditioner

Datasheet

2.5.4

Temperature Measurement

The temperature sensing diode, selected by TS – configuration bit 5, is biased with a constant current of 40µA.

It‘s forward drop changes with –2.1mV/°K typically, and is passed as differential temperature signal. The 40µA

current source is only on during temperature measurement, to prevent any interference with the bridge sensor

signal's measurement. The differential temperature signal is resolved by the ADC with only 10 bits, against a

differential reference voltage of 0.980V, derived from an on-chip bandgap. Whenever measuring temperature,

The CMC performs the sensor signal fine-tuning in the digital domain. It is a 16 bit RISC micro-controller, driven

by an on-chip clock generator with a nominal clock frequency of 1.5 MHz. The overall clock frequency tolerance

is smaller than ±25%. The CMC includes a 16-bit width ALU and a (16 x 16)-bit RAM. Furthermore it has a 12-

bit input counter into which the ADC will serially transmit conversion results; 4096 clock cycles are needed per

result. The CMC is connected to a (1k x 16)-bit instruction ROM and a (12 x 16)-bit parameter EEPROM. At the

output side the CMC is equipped with an I

Initially, during calibration, the same interface is used bi-directionally: to write the configuration word into the

EEPROM, to read non-corrected sensor value as well as temperature, and again and finally to write the valid

calibration parameters into the EEPROM.

The parameter EEPROM is a non-volatile store for 12 parameter values, each with 16 bits of width.

Address

Parameter

Default content

calibration parameter a0 for sensor's non-linearity correction

calibration parameter a1 for sensor's offset correction

calibration parameter a2 for first order sensor offset drift correction

calibration parameter a3 for second order sensor offset drift correction

calibration parameter a4 for gain correction

calibration parameter a5 for first order gain drift correction

calibration parameter a6 for second order gain drift correction

low-side scale limit value for corrected sensor signal

high-side scale limit value for corrected sensor signal

configuration word

customer-specific identification word

customer-specific identification word

Contents of the parameter EEPROM

The configuration word and it's contents under address &H09 have been described already in chapter 2.5.

The calibration parameters are stored under addresses &H00 through &H06. The calculation of these

parameters is described in the ZMD31020 Functional Description.

2.6

Correction Microcontroller CMC

2.7

Parameter EEPROM