SLAAEF1 august   2023 AFE11612-SEP

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Laser and Semiconductor Optical Amplifier Biasing
  6. 3EML Negative Bias Voltage
  7. 4Photodiode Detection Measurement
  8. 5Variable Optical Attenuator Control
  9. 6Summary
  10. 7References

3 EML Negative Bias Voltage

Optical networking applications that use an electro-absorption modulated laser (EML) require a negative voltage to bias the integrated electro-absorption modulator (EAM). The AFE11612-SEP has an internal 2.5-V reference that scales the DAC output range from 0 V to 5 V. The DAC output can be converted to a negative voltage through the use of an inverting op amp circuit that is powered by a negative power supply. The circuit in Figure 3-1 uses the op amp OPA4H199-SEP to offset and scale the 5-V output range to 0 V to -5 V. The feedback resistor ratio can be selected for an increased or decreased output range. The plot in Figure 3-2 shows the OPA output voltage vs the input DAC voltage.

GUID-20230727-SS0I-SNVS-PSTV-JXWT9ZX9K91P-low.svg Figure 3-1 Inverting Op Amp Circuit
GUID-20230727-SS0I-SJ2D-HDSQ-WDWKR1FNGHM9-low.svg Figure 3-2 Inverting Op Amp Output