Log-ratio amplifier has six-decade dynamic range

摘要

You need optical-power monitoring to guarantee overall system performance in fiber-optic communication systems. Logarithmic-signal processing can maintain precise measurements over a wide dynamic range. The wide-dynamic-range signal undergoes compression, and the use of a lower resolution measurement system then saves cost. As an example of this technique, consider a photodiode with responsivity of 0.5A/W that converts light energy to a current of 100nA to 1mA. With a four-decade dynamic range and 1% error, the required measurement resolution is 0.01 x 10~(-4), or 1 ppm. This measurement requires a 20-bit ADC.