|ADC0817||8-Bit μP Compatible A/D Converters with 16-Channel Multiplexer|
National ->Texas Instruments
|ADC0817 Datasheet PDF : 14 Pages |
The successive approximation register (SAR) performs 8 it-
erations to approximate the input voltage. For any SAR type
converter, n-iterations are required for an n-bit converter. Fig-
ure 2 shows a typical example of a 3-bit converter. In the
ADC0816, ADC0817, the approximation technique is extend-
ed to 8 bits using the 256R network.
The A/D converter's successive approximation register (SAR)
is reset on the positive edge of the start conversion (SC)
pulse. The conversion is begun on the falling edge of the start
conversion pulse. A conversion in process will be interrupted
by receipt of a new start conversion pulse. Continuous con-
version may be accomplished by tying the end-of-conversion
(EOC) output to the SC input. If used in this mode, an external
start conversion pulse should be applied after power up. End-
of-conversion will go low between 0 and 8 clock pulses after
the rising edge of start conversion.
The most important section of the A/D converter is the com-
parator. It is this section which is responsible for the ultimate
accuracy of the entire converter. It is also the comparator drift
which has the greatest influence on the repeatability of the
device. A chopper-stabilized comparator provides the most
effective method of satisfying all the converter requirements.
The chopper-stabilized comparator converts the DC input sig-
nal into an AC signal. This signal is then fed through a high
gain AC amplifier and has the DC level restored. This tech-
nique limits the drift component of the amplifier since the drift
is a DC component which is not passed by the AC amplifier.
This makes the entire A/D converter extremely insensitive to
temperature, long term drift and input offset errors.
Figure 4 shows a typical error curve for the ADC0816 as
measured using the procedures outlined in AN-179.
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