ST10F272M-4Q3 STMICROELECTRONICS [STMicroelectronics], ST10F272M-4Q3 Datasheet - Page 138

• Manufacturer Part Number: ST10F272M-4Q3
• Description: 16-bit MCU with 256 Kbyte Flash memory and 20 Kbyte RAM
• Manufacturer: STMICROELECTRONICS [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 42. 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
Anti-Aliasing Filter (f
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
charge transfer transient) will be much higher than V
respected (charge balance assuming now C
L
Analog Source Bandwidth (V
42).
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
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
f
f
must also be sized according to the current limitation constraints, in
cannot be modified by the analog signal source during the time in which
0
F
⋅
(
F
F
), according to Nyquist theorem the conversion rate f
S
C
= RC Filter pole)
Noise
). Again the conversion period T
+
10 τ 2
(source impedance) and R
F
C
⋅
f
f
P1
F
S
is definitively much higher than the sampling time T
+
, C
=
). The filter is typically designed to act as anti-aliasing (see
A
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
⋅
Sampled Signal Spectrum (f
⋅
(
C S
(
)
T
f
2 f
L
C S
F
S
=
: again considering the worst case in which C
C
, then the final voltage V
= f
V A C F
0
+
≤ 2 R
F
+
≤ f
0
C P1
(that is typically bigger than the on-chip
⋅
C P1
(Anti-aliasing Filtering Condition)
C
S
f
0
(Nyquist)
F
already charged at V
+
C
+
F
+
F
V A1
C P2
(filter resistance). Being C
C P2
(Conversion Rate vs. Filter Pole)
A1
⋅
C
(
)
C P1 C P2
F
)
. The following equation must be
is longer than the sampling time
C
≤
F
T S
+
f
of the filter is very high with
C
C
= conversion Rate)
A2
+
C S
(at the end of the
A1
)
S
):
, a constraint on
f
C
must be at
ST10F272M
F
S
, so the
P2