M02014 Datasheet, PDF (17/19 Pages) M/A-COM Technology Solutions, Inc. – CMOS Transimpedance Amplifier with AGC for Fiber Optic Networks up to 2.5 Gbps

Applications Information
After the TIA is turned on, the DC servo and AGC circuits attempt to null any input currents (up to the absolute
maximum stated in Table 1-1) as shown by the I/V curve in Figure 4-6.
Figure 4-6. TIA Use with Externally Biased Detectors, Powered On
-300
-200
1000
800
600
400
200
-100
0
0
-200
-400
-600
-800
-1000
PINA biased
100
200
300
400
500
600
700
mV
It can be seen that any negative voltage below 200 mV is nulled and that any positive going voltage above the PINA
standing voltage is nulled by the DC servo. The DC servo upper bandwidth varies from part to part, but is generally
at least 50 kHz.
When externally biasing a detector such as an APD where the supply voltage of the APD exceeds that for PINA
Table 1-1, care should be taken to power up the TIA first and to keep the TIA powered up until after the power
supply voltage of the APD is removed. Failure to do this with the TIA unpowered may result in damage to the input
FET gate at PINA. In some cases the damage may be very subtle, in that nearly normal operation may be
experienced with the damage causing slight reductions in bandwidth and corresponding reductions in input
sensitivity.
02014-DSH-001-D
Mindspeed Technologies^®
15
Mindspeed Proprietary and Confidential