E20-10
User Manual
6.5.4. ADC input connecting
Some nitty-gritty issues on ADC input connecting are described herein.
6.5.4.1.
Intrinsic input current of ADC analog input
This current was amplifier component property applied in revision A. Amplifier with
incomparably lower input current (about 10 nA) may be applied in revision B. But, due to the fact
of input current existence of revision A could be used in different propositions (for example, as
signal external source connecting sign), that in revision B the negative offset current can be live on
command (therewith, offset current is generated artificially) to be compatible with old revision, but
input offset current is dead
by default in revision B
ADC input intrinsic current of
E20-10
of revision А has negative sign, so,
when
unconnected analog input of E20-10
the overswing to negative values side will be appeared
.
This, on the one hand, leads to determinacy of unconnected analog input state, one the other hand,
places restrictions on signal internal resistance on direct current, because intrinsic input current
value multiplied by internal resistance of signal source (via direct current) will supply constant
voltage of input offset signal of
E20-10.
For example, if source resistance is of 50 Ohm typical
offset voltage will make 0.35 mV, and if 1 kOhm — 7 mV.
Fig. 6-5. Equivalent circuits of ADC input circuit via constant current (differences in
revisions A and B)
6.5.4.2.
Connecting to high-resistance output and alternate
current output
For E20-10
of revision А
, if your signal source outputs is alternate current output
containing series coupling capacitor (i.e. on direct current – disconnection or resistance of more
than 10 kOhm), then when connecting to such output it is required to connect additionally parallel
resistor (max. 1 kOhm preferably) to signal source output
. This resistor generates the required
18
Of course, such resistor connectivity depends on type and output capability of signal source
Более
5 MOм
7 мкА
(тип.)
Вход ревизия А
10 MOм
0.6 мкА
(тип.)
Вход ревизия B
управляется программно
(“по умолчанию” - выключен)
Input
revision A
Input
revision B
controlled in software
("by default" – off)
0.6 µA
(typical)
10 MOhm
7 µA
(typical)
Maximum
5 MOhm
