enabled and whether this input is single-ended or differential.
In the differential case, it also assigns the polarity of the
channels. Differential inputs are restricted to adjacent chan-
nel pairs. For example channel 0 and channel 1 may be
selected as a different pair but channel 0 or 1 cannot act
differentially with any other channel. In addition to selecting
differential mode the sign may also be selected. Channel 0
may be selected as the positive input and channel 1 as the
negative input or vice versa. This programmability is best
illustrated by the MUX addressing codes shown in the fol-
lowing tables for the various product options.
Functional Description
1.0 multiplexer Addressing
The design of these converters utilizes a sample-data com-
parator structure which provides for a differential analog
input to be converted by a successive approximation routine.
The actual voltage converted is always the difference be-
tween an assigned “+” input terminal and a “−” input terminal.
The polarity of each input terminal of the pair being con-
verted indicates which line the converter expects to be the
most positive. If the assigned “+” input is less than the “−”
input the converter responds with an all zeros output code.
The MUX address is shifted into the converter via the DI line.
Because the ADC0831 contains only one differential input
channel with a fixed polarity assignment, it does not require
addressing.
A unique input multiplexing scheme has been utilized to
provide multiple analog channels with software-configurable
single-ended, differential, or a new pseudo-differential option
which will convert the difference between the voltage at any
analog input and a common terminal. The analog signal
conditioning required in transducer-based data acquisition
systems is significantly simplified with this type of input
flexibility. One converter package can now handle ground
referenced inputs and true differential inputs as well as
signals with some arbitrary reference voltage.
The common input line on the ADC0838 can be used as a
pseudo-differential input. In this mode, the voltage on this pin
is treated as the “−” input for any of the other input channels.
This voltage does not have to be analog ground; it can be
any reference potential which is common to all of the inputs.
This feature is most useful in single-supply application where
the analog circuitry may be biased up to a potential other
than ground and the output signals are all referred to this
potential.
A particular input configuration is assigned during the MUX
addressing sequence, prior to the start of a conversion. The
MUX address selects which of the analog inputs are to be
TABLE 1. Multiplexer/Package Options
Number of Analog Channels
Part
Number
Number of
Single-Ended
Differential
Package Pins
ADC0831
ADC0832
ADC0834
ADC0838
1
2
4
8
1
1
2
4
8
8
14
20
13
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