ONET8531T_17 Datasheet, PDF (10/17 Pages) Texas Instruments – 11.3 Gbps Limiting Transimpedance Amplifier With RSSI

ONET8531T
SLLS891B – FEBRUARY 2008 – REVISED AUGUST 2011
APPLICATION INFORMATION
www.ti.com
Figure 15 shows the ONET8531T being used in a typical fiber optic receiver circuit using the internal photodiode
bias. The ONET8531T converts the electrical current generated by the PIN photodiode into a differential output
voltage. The FILTER inputs provide a DC bias voltage for the PIN that is low pass filtered by the combination of
an internal 220 Ω resistor and a capacitor. Because the voltage drop across the 220 Ω resistor is sensed and
used by the bias circuit, the photodiode must be connected to the FILTER pads for the bias to function correctly.
The RSSI output is used to mirror the photodiode output current and can be connected using a resistor to GND.
The voltage gain can be adjusted for the intended application by choosing the external resistor; however, for
proper operation of the ONET8531T, ensure that the voltage at RSSI never exceeds V_CC–0.65 V. The RSSI
output should be left open if it is not used while operating with internal PD bias.
The OUT+ and OUT– pins are internally terminated by 50 Ω pull-up resisters to VCC. The outputs must be AC
coupled, for example by using 0.1 μF capacitors, to the succeeding device.
VCC_OUT
VCC_IN
GND
3
2
1
4
19
5 ^{220 W}
18
17
6
16
7
15
14
8
9
10
11
12
13
R_RSSI
0.1 mF
OUT+
0.1 mF
OUT-
RSSI
Figure 15. Basic Application Circuit for PIN Receivers
10
Copyright © 2008–2011, Texas Instruments Incorporated