M68HC16 Z SERIES
ANALOG-TO-DIGITAL CONVERTER
USER’S MANUAL
8-15
Figure 8-4 Analog Input Circuitry
Since the sample amplifier is powered by V
DDA
and V
SSA
, it can accurately transfer
input signal levels up to but not exceeding V
DDA
and down to but not below V
SSA
. If
the input signal is outside of this range, the output from the sample amplifier is clipped.
In addition, V
RH
and V
RL
must be within the range defined by V
DDA
and V
SSA
. As long
as V
RH
is less than or equal to V
DDA
, and V
RL
is greater than or equal to V
SSA
, and
the sample amplifier has accurately transferred the input signal, resolution is ratiomet-
ric within the limits defined by V
RL
and V
RH
. If V
RH
is greater than V
DDA
, the sample
amplifier can never transfer a full-scale value. If V
RL
is less than V
SSA
, the sample am-
plifier can never transfer a zero value.
shows the results of reference voltages outside the range defined by V
DDA
and V
SSA
. At the top of the input signal range, V
DDA
is 10 mV lower than V
RH
. This
results in a maximum obtainable 10-bit conversion value of 3FE. At the bottom of the
signal range, V
SSA
is 15 mV higher than V
RL
, resulting in a minimum obtainable 10-bit
conversion value of three.
SAMPLE
AMP
8 CHANNELS TOTAL
1
RC DAC
ARRAY
COMPARATOR
REF 1
V
SSA
V
RL
REF 2
V
DDA
V
RH
ADC 8CH SAMPLE AMP
1. TWO SAMPLE AMPS EXIST ON THE ADC WITH EIGHT CHANNELS ON EACH SAMPLE AMP.
NOTES:
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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