4

Rev. 5/14/03

SP8034A APC Amplifier with Integrated Photodetector

© Copyright 2003 Sipex Corporation

A major consideration in developing the optical

pick-up head system is the extremely small form

factor, which is additionally aggravated by the

physical locations required by the light path.

Special care must be taken when designing the

Flex or PCB for this part. The output peak

current requirement is in the order of 12.5 mA

when driving 50pF of capacitive load with a

slew rate of 250V/

µs. Therefore care must be

taken to provide low inductance, low resistance

paths for power and ground and output traces.

Supply coupling is also very important. Good

supply decoupling is important to ensure the

high frequency performance of the system by

eliminating supply lead inductance effects. The

decoupling capacitor C1, as shown in Figure 5,

should be as close to the part as possible.

This capacitor should be 0.1

µF ceramic. C2 is

optional to improve decoupling and is recom-

mended to be 1

µF tantalum. The layout of the

PCB is pictured here. Note the wide and short

traces on the supply lines.

excessive parasitics. Any parasitics on these

nodes will limit the performance of the system.

ometers in the application. This is a single layer

board using FR4 material.

In order to minimize coupling capacitance into

the gain setting resistor nodes, it is also critical

traces associated with the gain-setting resistors.

1

2

3

4

8

7

6

5

GAIN

GND

400

400

RL

1k

C2

0.1µF

+

+

CL1

50pF

RS

Depends

on FPC

+

C1

0.1µF

GAIN

+5V

SP8034A

®

Figure 5. Test Circuit - Cload = 50p, V

GAIN

GND

GND

RL

R2

R1

CR

PIN

Figure 4. Evaluation Board.

LAYOUT AND ROUTING CONSIDERATIONS