Low power wide spectrum optical transmitter using avalanche mode LEDs in SOI CMOS technology

Abstract

This paper presents a low power monolithically integrated optical transmitter with avalanche mode light emitting diodes in a 140 nm silicon-on-insulator CMOS technology. Avalanche mode LEDs in silicon exhibit wide-spectrum electroluminescence (400 nm < λ < 850 nm), which has a significant overlap with the responsivity of silicon photodiodes. This enables monolithic CMOS integration of optocouplers, for e.g. smart power applications requiring high data rate communication with a large galvanic isolation. To ensure a certain minimum number of photons per data pulse (or per bit), light emitting diode drivers must be robust against process, operating conditions and temperature variations of the light emitting diode. Combined with the avalanche mode light emitting diode's steep current-voltage curve at relatively high breakdown voltages, this conventionally results in high power consumption and significant heating. The presented transmitter circuit is intrinsically robust against these issues, thereby enabling low power operation.

Data Transmission Capabilities of Silicon Avalanche Mode Light-Emitting Diodes

“…For an optical link, the photon transmission to a nearby photodetector is important. We have already shown a linear relation between Q b and the emitted photon flux from an AMLED [5], [18]. Therefore, triggering of an avalanche during a data bit impacts the light emission from an AMLED for that bit [18], [24].…”

“…We briefly describe the functionality of this circuit. For further details of this circuit, we refer the reader to [18], in which we have demonstrated an integrated implementation of this driver circuit. Initially the AMLED is biased below V BR and then V AMLED = V LOW = V BIAS −V DD .…”

“…The maximum Q b equals C Q V EX,i : In this work, the circuit of Fig. 6(a) was designed on a printed circuit board (PCB) which, in contrast to the CMOS integrated implementation of [18], resulted in C P ∼ 20 pF.…”

“…Fig.6. (a) Schematic layout of an AMLED driver circuit to measure modulation speed[18]. The I AMLED was measured directly on the oscilloscope.…”

“…In our experimental setup, three C Q settings were incorporated: 470 pF, 800 pF and short (C Q → ∞). A simplified model for the AMLED is also shown[18]. (b) Illustrative transient waveforms.where T ON is the pulse width of the control signal IN.Due to the relatively low internal quantum efficiency of AM-LEDs (10 −5 )[18], high speed optical measurements are not possible using conventional photodetectors.…”