20GHz to 480GHz on-chip broadband spectrometer in 65-nm CMOS technology

The implementation and characterization of a 20 GHz to 480 GHz continuously tunable on-chip spectrometer in 65-nm CMOS technology is presented. The structure consists of a pulse generator based on a meandered nonlinear transmission line, a passive pulse differentiator and a high-speed sample and hold-circuit. Time domain and frequency domain measurements have been performed to characterize the spectrometer. A 3.1 ps fall time of the sampler is derived under optimized bias conditions. The spectrometer generates and detects a tunable frequency comb with frequency components between 20 GHz and 480 GHz, with a signal to noise ratio of 90 dB at 100 GHz, 70 dB at 200 GHz and 40 dB at 480 GHz. Due to the on-chip implementation of the transmitter and sampler, no external lenses are required and the circuit is integrated in an area of 3 mm². It can be used for on-chip analysis of e.g. droplets in a microfluidic package.