A variable transimpedance preamplifier for use in wide dynamic range optical receivers

A preamplifier with an automatic gain control (AGC) function based on a new circuit configuration suitable for monolithic integration is proposed as an approach for realizing optical receivers with wide dynamic ranges. This new preamplifier, intended for transmission systems operating above 100 Mb/s, is designed for fabrication using 3-μm Si-bipolar IC technology. The fabricated IC exhibits a bandwidth of more than 220 MHz and an equivalent input noise current of about 3 pA/√Hz at a maximum transimpedance of 18 kΩ. To examine the AGC capability of the new preamplifier IC, a 140-Mb/s transmission experiment was carried out using a laser diode (LD) transmitter and a p-i-n receiver with its gain controlled by the new preamplifier. An optical dynamic range of 21.5 dB was achieved and thus it should be possible to realize optical receivers with wide dynamic ranges using this preamplifier.