ONET8531T Datasheet, PDF (11/15 Pages) Texas Instruments – 11.3 Gbps Limiting Transimpedance Amplifier With RSSI

ONET8531T
www.ti.com
SLLS891 – FEBRUARY 2008
Figure 16 shows the ONET8531T being used in a typical fiber optic receiver circuit using an external photodiode
bias for an APD photodiode. This configuration can also be used for a PIN diode. The external bias RSSI signal
is based on a DC offset value and is not as accurate as the internal bias RSSI signal, which is based upon the
photodiode current.
VCC_OUT
VCC_IN
APD_BIAS
3
2
1
4
19
5 ^{220 W}
18
17
6
16
7
15
14
8
9
10
11
12
13
0.1 mF
OUT+
0.1 mF
OUT-
GND
Figure 16. Basic Application Circuit for APD Receivers
ASSEMBLY RECOMMENDATIONS
You need to concentrate on assembly parasitics and external components to achieve optimal performance.
Recommendations that optimize performance include:
1. Minimize the total capacitance on the IN pad by using a low capacitance photodiode and compensating for
stray capacitances. Place the photodiode close to the ONET8531T die in order to minimize the bond wire
length and associated parasitic inductance.
2. Use identical termination and symmetrical transmission lines at the AC coupled differential output pins OUT+
and OUT–.
3. Use short bond wire connections for the supply terminals VCC_IN, VCC_OUT and GND. Supply voltage
filtering is provided on chip but filtering may be improved by using an additional external capacitor.
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): ONET8531T
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