A 10-Gb/s Inductorless CMOS Limiting Amplifier for Optic-Fiber Transmission System

A 10-Gb/s inductorless limiting amplifier for optic-fiber transmission system is designed and fabricated in a 0.18-μm CMOS technology. The whole circuit consists of an input buffer, three broadband gain stages, an output buffer for driving 50-Ω transmission lines and a DC offset cancellation circuit. By employing a third-order interleaving active feedback, the bandwidth of the proposed circuit can be effectively enhanced while maintaining a suppressed gain peaking within the frequency band. Consuming a DC power of 72 mW from a 1.8-V supply voltage, this limiting amplifier exhibits a voltage gain of 42 dB and a -3-dB bandwidth of 8.6 GHz, and it allows an input dynamic range of at least 40 dB. With a pseudo-random bit sequence at 10 Gb/s, the measured output swing and input sensitivity are about 350 mVpp and 10 mVpp, respectively. Due to the absence of the spiral inductors, the chip size of this limiting amplifier including the pads is 0.58 × 1.06 mm², where the active circuit area only occupies 285 × 600 μm².