Rainbow Electronics AT77C101B FingerChip™ - Manual (Page 17)

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AT77C101B
2150A–BIOM–02/02
Integration Time and
Clock Jitter The AT77C101B is not very sensitive to clock jitter (clock variation). The most important
requirement is a regular integration time that ensures the frame reading rate is also as
regular as possible, in order to get consistent fingerprint slices.
If the integration time is not regular, contrast will vary from one frame to another.
Note that it is possible to introduce some waiting time between each set of 1124 clock
pulses, but the overall time of one frame read must be regular. This waiting time is gen-
erally the time needed by the processor to perform some calculation over the frame (to
detect the finger, for instance).
Figure 12. Read One Frame
Figure 13. Regular Integration Time
Clock PCLK
Reset RST is low
1 2 3 4 5 6 1124 1123 1122 1121 1120 1119
Column 1 Column 2 Column 280 Dummy Column 281
Pixels 1 & 2 3 & 4 5 & 6 7 & 8 1 & 2 3 & 4 7 & 8 DB1 DB2 DB3 DB4
Clock PCLK
REGULAR INTEGRATION TIME
Frame n
1124 pulses
Frame n+1
1124 pulses
Frame n+2
1124 pulses
Frame n+3
1124 pulses