M02011 Datasheet, PDF (14/22 Pages) M/A-COM Technology Solutions, Inc. – CMOS Transimpedance Amplifier with AGC for Fiber Optic Networks up to 622 Mbps

M02011
CMOS Transimpedance Amplifier with AGC
for Fiber Optic Networks up to 622 Mbps
Rev V5
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
monitoring 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)
4
Optical Power (dBm)
+6
2
+3
1
0
0.5
–3
Rm (Ω)
500
1000
2000
4000
14
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