EPC901 Datasheet, PDF (31/37 Pages) Espros Photonics corp – CCD line sensor 1024x1 pixel

13.3. Layout recommendations
13.3.1. Electrical
The epc901 line imager is a very high sensitivity analog/digital chip. Due to its high conversion gain, just a few electrons collected by
coupling to signal lines close to the chip generate a significant voltage at the output. Thus, do not place any signal lines underneath the
chip without shielding. It is highly recommended to place a stable AGND plane underneath the epc901 chip (on the top layer of the PCB)
and not to place any signal tracks close to the chip.
Also very important is a clean noise-free power supply. Especially decouple the VDD from VDD_OA with capacitor so the output modula -
tion of the video amplifier does not modulate the VDD of the chip. Make sure all the capacitors used for decoupling are low ESR types.
The READ signal line can also be a major source of noise or coupling to the output signal. Figure 15 shows a scope screenshot of such a
coupling problem.
VIDEO_P
READ
Figure 15: Bad READ signal coupling to the output by a ground loop
The source of such problems is usually a ground loop. Especially if there is a significant distance 'd' as shown in Figure 16 (starting from a
few cm only) between the video output of the epc901 chip and the input of the ADC. Care has to be taken that the layout of the GND lines
is exactly like shown in Figure 16. Make sure that the digital GND has a separate track as shown by the blue ground line!
d
26
10
12
32 _{VDD_1V8}
18 _{VDD_5V0}
20 _{VDD_7V0}
epc 901
VIDEO_P ⁹
VIDEO_N ⁸
31
1 16
7
VDD
ADC
AGND
VDD
Common AGND
connection
Digital
control
READ
DGND
GND
Common GND
connection
Figure 16: Recommended ground and power supply connections
Make also sure that the thick lines in Figure 16 are as short and as thick as possible.
© 2016 ESPROS Photonics Corporation
Characteristics subject to change without notice
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