Datasheet

1139
SAM4S Series [DATASHEET]
11100F–ATARM–29-Jan-14
Track and Hold Time versus Source Output Impedance
Figure 44-17 shows a simplified acquisition path.
Figure 44-17. Simplified Acquisition Path
In 12-bit mode, during the tracking phase, the ADC needs to track the input signal during the tracking time shown below:
t
TRACK
= 0.054 x Z
SOURCE
+ 205
with t
TRACK
expressed in ns and Z
SOURCE
expressed in Ω.
The ADC already includes a tracking time of 15 t
CP_ADC
Two cases must be considered:
1. If the calculated tracking time (t
TRACK
) is lower than 15 t
CP_ADC
, then TRACTIM can be set to 0 .
2. If the calculated tracking time (t
TRACK
) is higher than 15 t
CP_ADC
, then TRACTIM must be set to the correct value.
Table 44-52. Z
IN
Input Impedance
f
S
(MHz) 1 0.5 0.25 0.125 0.0625 0.03125 0.015625 0.007813
C
IN
= 2 pF
Z
IN
(MΩ) 0.51248163264
C
IN
= 4 pF
Z
IN
(MΩ) 0.250.512481632
C
IN
= 8 pF
Z
IN
(MΩ) 0.125 0.25 0.5 1 2 4 8 16
Sample & Hold
12-bit ADC Core
C
IN
MUX
R
ON
Z
SOURCE