Philips Semiconductors

Product specification

NE5210

Transimpedance amplifier (280MHz)

1995 Apr 26

13

This represents the maximum limit attainable with the NE5210

operating at 200MHz bandwidth, with a half mark/half space digital

transmission at 850nm wavelength.

APPLICATION INFORMATION

Package parasitics, particularly ground lead inductances and

parasitic capacitances, can significantly degrade the frequency

response. Since the NE5210 has differential outputs which can feed

back signals to the input by parasitic package or board layout

capacitances, both peaking and attenuating type frequency

response shaping is possible. Constructing the board layout so that

Ground 1 and Ground 2 have very low impedance paths has

produced the best results. This was accomplished by adding a

ground-plane stripe underneath the device connecting Ground 1,

Pins 8–11, and Ground 2, Pins 1 and 2 on opposite ends of the

SO14 package. This ground-plane stripe also provides isolation

2 and the input photodiode currents to flowing to Ground 1. Without

this ground-plane stripe and with large lead inductances on the

board, the part may be unstable and oscillate near 800MHz. The

easiest way to realize that the part is not functioning normally is to

measure the DC voltages at the outputs. If they are not close to their

quiescent values of 3.3V (for a 5V supply), then the circuit may be

oscillating. Input pin layout necessitates that the photodiode be

physically very close to the input and Ground 1. Connecting Pins 3

and 5 to Ground 1 will tend to shield the input but it will also tend to

increase the capacitance on the input and slightly reduce the

bandwidth.

As with any high-frequency device, some precautions must be

observed in order to enjoy reliable performance. The first of these is

the use of a well-regulated power supply. The supply must be

capable of providing varying amounts of current without significantly

changing the voltage level. Proper supply bypassing requires that a

good quality 0.1

µF high-frequency capacitor be inserted between

pins as possible. Also, the parallel combination of 0.1

µF capacitors

with 10

the ground plane should provide adequate decoupling. Some

applications may require an RF choke in series with the power

supply line. Separate analog and digital ground leads must be

maintained and printed circuit board ground plane should be

employed whenever possible.

Figure 4 depicts a 50Mb/s TTL fiber-optic receiver using the BPF31,

850nm LED, the NE5210 and the NE5214 post amplifier.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

1

2

3

4

5

6

7

8

9

10

11

12

13

14

LED

CPKDET

THRESH

GNDA

FLAG

JAM

VCCD

VCCA

GNDD

TTLOUT

IN1B

IN1A

CAZP

CAZN

OUT1B

IN8B

OUT1A

IN8A

RHYST

RPKDET

GND

GND

GND

OUT

GND

GND

OUT

VCC

VCC

NC

IIN

NC

GND

GND

R2

220

D1

LED

C9

100pF

100pF

C7

.01

µF

47

µF

C1

C2

GND

+VCC

0.1

µF

R4

4k

R3

47k

VOUT (TTL)

L3

10

µH

L2

10

µH

C11

C10

.01

µF

.01

µF

C13

C12

10

µF

10

C8

L1

10

µH

BPF31

OPTICAL

INPUT

R1

100

C5

1.0

µF

C6

.01

µF

.01

µF

C4

10

µF

C3

NOTE:

The NE5210/NE5217 combination can operate at data rates in excess of 100Mb/s NRZ

The capacitor C7 decreases the NE5210 bandwidth to improve overall S/N ratio in the DC–50MHz band, but does create extra high frequency noise

on the NE5210 VCC pin(s).

SD00330

Figure 4. A 50Mb/s Fiber Optic Receiver