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Применения > > Interfacing the ADL5315 High Side Current Mirror to a Translinear Logarithmic Amplifier in a Photodiode Power Detector Application

Interfacing the ADL5315 High Side Current Mirror to a Translinear Logarithmic Amplifier in a Photodiode Power Detector Application (CN0056)

TheADL5315 addresses the need for precision high-side monitoring of PIN photodiode current in fiber optic systems and is useful in many nonoptical applications as well. It is optimized for use with the Analog Devices, Inc., family of translinear logarithmic amplifiers, which take advantage of the wide input current range of the ADL5315. The circuit presented in this document and shown in Figure 1 provides high accuracy power monitoring using the ADL5315 precision wide-range, high-side current mirror and the AD8305 translinear logarithmic amplifier (log amp). This configuration is ideal for high accuracy power monitoring because the full current mirror range (3 nA to 3 mA) of the ADL5315 can be used.



Figure 1: Connecting the ADL5315 to the AD8305


The measured rms noise voltage at the output of the AD8305 vs. the input current is shown in Figure 2, both for the AD8305 by itself and in cascade with the ADL5315. The relatively low noise produced by the ADL5315, combined with the additional noise filtering inherent in the frequency response characteristics of the AD8305, results in minimal degradation to the noise performance of the AD8305.


Figure 2: RMS Noise of AD8305 vs. AD8305 Cascaded with ADL5315

Возможности

  • High Side Current Monitor of PIN Photodiode
  • Translinear Logarithmic Amplifier
  • Wide Input Current Range 3nA - 3mA

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