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!

Digital

control

VIDEO_N

VIDEO_P

VDD_1V8

VDD_5V0

VDD_7V0

32

18

20

1

16

31

7

26

12

9

8

ADC

AGND

VDD

epc 901

DGND

READ

GND

VDD

d

Common AGND

connection

Common GND

connection

10

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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