st10f273m STMicroelectronics, st10f273m Datasheet - Page 144

• Manufacturer Part Number: st10f273m
• Description: 16-bit Mcu With 512 Kbyte Flash Memory And 36 Kbyte Ram
• Manufacturer: STMicroelectronics

Electrical characteristics
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The two transients above are not influenced by the voltage source that, due to the presence
of the R
C
respect to the sampling time (T
Figure
Calling f
the anti-aliasing filter, f
least 2f
the conversion period (T
T
selected (fastest conversion rate at a specific channel): In conclusion it is evident that the
time constant of the filter R
charge level on C
the sampling switch is closed.
Figure 43. Anti-aliasing filter and conversion rate
S
S
, which is just a portion of it, even when fixed channel continuous conversion mode is
with respect to the ideal source V
A second charge transfer involves also C
capacitance) through the resistance R
and C
time constant is:
In this case, the time constant depends on the external circuit: in particular imposing
that the transient is completed well before the end of sampling time T
R
Of course, R
combination with R
definitively bigger than C
transfer transient) will then be much higher than V
respected (charge balance assuming now C
L
43).
0
F
sizing is obtained:
0
; it means that the constant time of the filter is greater than or at least equal to twice
C
Analog source bandwidth (VA)
the bandwidth of the source signal (and as a consequence the cut-off frequency of
F
S
filter, is not able to provide the extra charge to compensate the voltage drop on
were in parallel to C
V A2 C S C P1 C P2 C F
S
L
shall be sized also according to the current limitation constraints, in
cannot be modified by the analog signal source during the time in which
f
⋅
f
(
0
F
F
), according to Nyquist theorem the conversion rate f
S
C
). Again the conversion period T
+
10 τ 2
(source impedance) and R
F
Noise
C
⋅
P1
F
S
is definitively much higher than the sampling time T
, C
+
f
f
=
). The filter is typically designed to act as anti-aliasing (see
P1
τ 2 R L
10 R
P2
<
(since the time constant in reality would be faster), the
A
⋅ L
and C
+
; the time constant R
⋅
⋅
(
C S
(
)
L
C S
S
=
Sampled signal spectrum (f
: again considering the worst case in which C
, the final voltage V
V A C F
TC ≤ 2 RFCF (Conversion rate vs. filter pole)
fF = f0 (Anti-aliasing filtering condition)
2 f0 ≤ fC (Nyquist)
+
F
+
C P1
(that is typically bigger than the on-chip
⋅
C P1
S
already charged at V
+
f
+
0
F
+
V A1
C P2
(filter resistance). C
C P2
A1
. The following equation must be
⋅
C
(
)
C P1 C P2
F
)
is longer than the sampling time
C
≤
F
T S
+
of the filter is very high with
A2
f
C
(at the end of the charge
C
+
= conversion rate)
C S
A1
)
S
F
):
, a constraint on
being
C
must be at
f
ST10F273M
S
, so the
P2