In long-reach passive optical networks (PONs), dispersion compensation is required because of the long reach and high bit rates. To enable such compensation, a team of researchers from Ireland’s Tyndall National Institute and University College Cork has developed circuitry for fast gain adaptation in a linear burst-mode receiver (BMRx). Their 10-Gb/s BMRx boasts impressive linearity over a dynamic range beyond 20 dB. It therefore enables electronic dispersion compensation or multilevel modulation formats in bursty optical inks. This receiver is the work of Peter Ossieur, Nasir A. Quadir, Stefano Porto, Cleitus Antony, Wei Han, Marc Rensing, Peter O’Brien, and Paul D. Townsend.
Their LBMRx, which comprises a variable-gain transimpedance amplifier (TIA) and variable-gain post amplifier, achieves gain of 47 to 85 dBΩ on a single die. At 84 dBΩ, such gain allows for the elimination of the post-amplifier chip. To perform gain adjustment in less than 50 ns, the LBMRx uses replica-based, feed-forward automatic gain control (AGC) and peak detectors. Those detectors are reset between bursts using an external reset signal. Using a PIN photodiode, sensitivity of -23.2 dBm was measured at a bit-error rate (BER) of 1.1 x 10-3. Because a 0.5-dB penalty is incurred if a 0-dBm burst precedes the burst under consideration, the LBMRx can support a dynamic range of 22.7 dB. See “A 10 Gb/s Linear Burst-Mode Receiver in 0.25 μm SiGe:C BiCMOS,” IEEE Journal Of Solid-State Circuits, Feb. 2013, p. 381.