02011-DSH-001-C Datasheet, PDF (12/21 Pages) M/A-COM Technology Solutions, Inc. – CMOS Transimpedance Amplifier with AGC for Fiber Optic Networks up to 622 Mbps

Applications Information
4.2
Monitor Calibration
To achieve the best monitor accuracy, both the slope and calibrated offset should be used. The offset calibration is
achieved by measuring the dark current from the MON output. The calibrated monitor value is usually determined
by y = mx + b or:
I_{MON_CALIBRATED} = (Slope * I_{MON_READING}) + I_{MON_OFFSET}
Where Slope = 1/Imon_ratio (Table 1-4) = 1/0.7 = 1.43 and
I_{MON_OFFSET} = I_INPUT@CAL - (I_{MON_READING@CAL} * Slope)
4.3
Selecting the Monitor Resistor
As described earlier the high impedance monitor output sources a replica average photodiode current for monitor-
ing purposes. If detected by converting the current to a voltage through an external resistor (Figure 4-1), ensure
that the voltage on V_MON is in the range of 0 to 2V. The table below provides suggested values for the monitor
resistor.
Table 4-1. Selection of Rm for Maximum Input Current
I_IN Max (mA)
Optical Power (dBm)
4
+6
2
+3
1
0
0.5
-3
Rm (Ω)
500
1000
2000
4000
02011-DSH-001-C
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