An Analytical Design Method for High-Speed VCSEL Driver With Optimized Energy Efficiency

A universal analytical design approach for laser diode drivers (LDDs) is presented and verified. All design parameters are derived analytically, taking the vertical-cavity surface-emitting laser (VCSEL) characteristics into account. Two optimization strategies are proposed. First, the power consumption is minimized for the highest achievable optical modulation amplitude (OMA) and extinction ratio (ER). Second, the highest achievable data rate (DR) is considered to maximize the energy efficiency. As a result, a simple differential amplifier can be implemented as an LDD to achieve energy efficiencies and DRs comparable or even higher than the one of more complex designs utilizing preemphasis, feedforward equalization, and pulse amplitude modulation. Therefore, drivers designed with this holistic analytical approach accommodate well the demands for high DRs, high energy efficiency, high compactness, high reliability, and low latency in future optical data links. A compact LDD is designed with an active area of only 0.15 × 0.12 mm² in a 130-nm SiGe BiCMOS technology. A DR of 40 Gbit/s with bit error rates <; 10^-13 and an energy efficiency of 2.245 pJ/bit are achieved for an OMA of 1.1 mW and an ER of 10 dB using a 20-GHz 850-nm common-cathode VCSEL. The achieved values deviate less than 10% from the predicted ones, which clearly illustrates the effectiveness of the presented analytical approach. Further improvements are achieved by optimizing the modulation levels and the performance to the link requirements. At 45 and 30 Gbit/s, 1.8 and 1.17 pJ/bit are achieved, respectively.