Datasheet
Integrator
ResetSample
(SHR)
SignalSample
(SHS)
FiltBypass
FiltBypass
LPF
LPF
SHR
SHS
+
-
SHS-SHR
CDS
IRST
AFE0064
SLAS672 –SEPTEMBER 2009 ........................................................................................................................................................................................
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PIN FUNCTIONS (continued)
PIN
I/O DESCRIPTION
NUMBER NAME
49, 51, 52, VSS I Ground for device power supply
54, 59, 62,
65, 71, 73,
74, 76, 79,
80, 82, 85,
86, 90, 91,
99, 101, 102,
103, 107,
109, 110
TFT CHARGE INJECTION COMPENSATION
72 DF-SM I Digital control to dump compensation charge on integrator capacitor; this is useful to nullify the
effect of pixel TFT charge injection.
56 VT-A I External voltage to control the amount of charge dump for TFT charge injection compensation.
Charge dump = (V-voltage at 'EXT_C')*0.857 pC where V is external voltage at pins 56, 57. Short
pins 56 and 57 externally and apply external voltage for charge injection compensation.
57 VT-B I
NC PINS
58, 111 These pins should be connected to VSS.
DESCRIPTIONS AND TIMING DIAGRAMS
Figure 1. Integrator Channel Schematic
Figure 1 shows the typical schematic of an integrator channel. As shown, each integrator has a reset (IRST)
switch which resets the integrator output to the 'reset-level'. The device integrates input current while this switch
is open. There are two sample and hold circuits connected to each integrator output. SHR samples integrator
reset level output and SHS samples integrator output post integration of signal charge. The device subtracts the
SHR sample from the SHS sample. The difference is then available at device output in a differential format. This
action is called 'Correlated Double Sampling' (CDS). CDS removes integrator offset and low frequency noise
from device output.
Each sample and hold has a built-in low pass filter. This filter limits sampling bandwidth so as to limit sampled
noise to an acceptable level. Detailed functioning of individual blocks is described further with timing diagrams.
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