Functional Description; Input Circuitry - PEP Modular Computers Modular Computers RS485 User Manual

Chapter 5 Analog Modules
SMART I/O User's Manual

5.1.5 Functional Description

The SM-DAD1 has 4 differential voltage inputs and 2 unipolar/bipolar
voltage outputs. An on-board EEPROM contains board specific calibration
data, module ID byte and production data. An on-board switched-mode
regulator provides 15V for the analog I/O and an additional linear regulator
provides the -5V required by the ADC.

5.1.5.1 Input Circuitry

The input circuitry of the SM-DAD1 consists of an R-C first-order, low-pass
filter to prevent noise and signals greater than 10kHz from entering the
system, a 1:4 channel multiplexer, followed by a differential amplifier,
divider and a 12-bit fast analog to digital converter (ADC).
Figure 5.1.5.1: SM-DAD1 Input Schematic Diagram
+
System
Low Pass Input
Voltage
MUX
ADC
Interface
Amplifier
Source Filter
4:1
-
-10 .. +10V
Single
Ended
AGND
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.
March 12, 1996
Page 5 - 10 ©1996 PEP Modular Computers GmbH