TC1796
Peripheral Units (Vol. 2 of 2)
Fast Analog-to-Digital Converter (FADC)
User’s Manual
26-22
V2.0, 2007-07
FADC, V2.0
26.1.8
Offset and Gain Calibration
The offset and gain calibration is used to minimize the error of the FADC conversion
results independently for each channel. The output of each channel amplifier can be
adjusted to deliver a minimum offset value for zero input voltage difference. The channel
which is calibrated is selected by GCR.CALCH. The calibration mode is selected by
GCR.CALMODE. During the calibration process of a channel, the other channels can be
used in normal conversion mode without restrictions.
Figure 26-11 Analog Input and Channel Amplifier Configuration at Calibration
shows the channel amplifier configuration as well as the analog input pin
configurations that are selected during offset and gain calibration. Note that in the
calibration modes, the impedance of the analog inputs depends on the settings of the
ENN and ENP bits of the corresponding Channel x Analog Control Register ACRx.
MCA06048
Rp
Rn
V
FAGND
V
FAREF
/2
Analog Input Configuration
during Offset/Gain Calibration
V
FAREF
/2
High
Impedance
High
Impedance
ACRx.ENN = ACRx.ENP = 1
Other combinations than
ACRx.ENN = ACRx.ENP = 1
Offset Calibration
(GCR.CALMODE = 01
B
)
Channel
Amplifier
Gain Calibration
(GCR.CALMODE = 10
B
)
V
FAREF
/2
-
+
+
-
Channel
Amplifier
FAINxP
FAINxN
FAINxP
FAINxN