Pepper Computer Modular Computers RS485 - Manual (Page 247)

SMART I/O User’s Manual
©1996 PEP Modular Computers GmbH October 01, 1996 Page 5 - 91
5
Chapter 5 Analog Modules
5.4.5 Functional Description
The SM-ADC1 has 6 differential voltage or current inputs depending on the
ordered type. An on-board EEPROM contains board specific calibration
data, module ID byte, sub ID byte and production data. A DC/DC converter
generates the 5V to ± 15V power requirements for the ADC converter and
provides additional system isolation.
5.4.5.1 Input Circuitry
The input circuitry of the SM-ADC1 consists of an R-C first-order, low-pass
filter to prevent noise and signals greater than 10kHz from entering the
system, a 1:6 channel multiplexer, followed by a differential amplifier,
divider and a 12-bit fast analog to digital converter (ADC).
Figure 5.4.5.1: SM-ADC1 Input Shematic Diagram
The ADC, using successive approximation and input track and hold is
referenced by its own on-chip voltage source supplying 4.096V. To cater for
bipolar full-scale inputs, this reference source is split (-2.048V .. +2.048V).
The incoming voltage signals are multiplexed and reduced via a 1:5 divider
network so that the ADC is supplied with a scalable input voltage range.
Low Pass
Filter
Voltage
Source
-10 .. +10V
Single
Ended
AGND
+
-
MUX
8:1
Input
Amplifier
ADC
System
Interface