A 56 Gbit/s 0.35 µm SiGe Limiting Amplifier with 2.4 THz Gain-Bandwidth-Product

A limiting amplifier implemented in 0.35 μm SiGe-bipolar technology for bit rates up to 56 Gbit/s is presented. The amplifier input sensitivity for a bit error rate of 10^(-6) is 7 mVpp at 12.5 Gbit/s and 25 mVpp at 50 Gbit/s. The large-signal bandwidth at a sinusoidal input voltage of 56 mVrms is 41 GHz and the small-signal gain-bandwidth-product at an input voltage of 5.6 mVrms is 2.4 THz. The output differential voltage swing can be varied from 0.36 Vpp to 1.8 Vpp. The circuit can operate from a 1.9 V to 3.0 V supply and consumes 38 mW to 420 mW depending on the supply and bias control voltage. The circuit consists of a main output path and two auxiliary paths that can be controlled independently of the main one. The amplifier gain cells employ emitter followers and a differential pair amplifier without any inductive peaking.