Intel 8253 - Page 215

Sampling Pulse
-V
o
V
o
Sample
Hold
T
A
E
A
Aperture
Error
Aperture
Uncertainty
in
N
ref
LSB
A
fVf
V
T
pp 2
1
=<
⇒=
+
AO
1n
O
TfV2
2
2V
p
1n
O
AA
2
2V
LSB 1/2
dt
dV
TE
+
===
ft2sinVV
O
p=
O
max
fV2
dt
dV
p =
ftcos2fV2
dt
dV
O
pp=
ADC
f
CLK
APERTURE ERROR
Analog and Mixed-Signal Center (ESS)
The aperture error comes from the fact that there is a delay
between the clock signal and the effective holding time.