Datasheet

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last update
November 30, 2010
reference
smtutin
page
13/27
6.4 Mode 3. CMUX: X capacitors 0-2pF/0-12pF, external MUX
In this mode, an arbitrary number of capacitors in the range of 0 - 2 pF (CML = 0) or the range of 0 - 12 pF (CML = 1) with a
common electrode can be measured. The UTI does not perform a phase selection, so an external multiplexer should be used.
Just for this application, Smartec developed a novel multiplexer MUX with nine outputs and four inputs. The specifications of the
CMUX mode are listed in Table 9. A possible measurement setup is shown in Figure 7 . An external multiplexer, which is
controlled by the microcontroller (µC), multiplexes the signal at node B to one (or more) of the capacitors. The UTI output
appears on the node “output”. Nominal frequencies of the output signal during an offset measurement (none of the capacitors
are selected) are 6 kHz (SF = 1) and 50 Hz (SF = 0). More information about this UTI mode can be found in the specifications
of the Multiplexer.
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Figure 7. Possible measurement setup in the CMUX mode to measure multiple capacitors
Parameter Typical value Typical value
(CML=0) (CML=1)
K
1
10 s/pF 1,7 s/pF
C
0ff
2 pF 12 pF
Max cap value (C
xa
) 2 pF 12 pF
Linearity 13 bits 13 bits
Resolution (SF=0) 14 bits 14 bits
Remaining offset < 2 x10
-5
pF < 2 x10
-5
pF
Table 9. specifications of the CMUX mode
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