Quadrature amplitude modulation frequency up- and down-conversions using a positive-intrinsic-negative photodiode sampling mixer

Simulation and experimental performance analysis of a positive-intrinsic-negative photodiode (PIN-PD) sampling mixer used as frequency up and down-converters are presented. Besides, a frequency mixing with a PIN-PD can operate in a frequency range up to 47.3 GHz for up-conversion and 38.5 GHz for down-conversion. The design and operating regime peculiarities of a PIN-PD as an up and down-converter in a radio over fiber (RoF) system are also discussed. The conversion gain of a PIN-PD sampling mixer is simulated and measured. We showed that the gain may decrease from 27 dB at a mixing frequency of 8.3 GHz to 3 dB at the one with 47.3 GHz in an up-conversion mode and from 26.5 dB at 31.7 GHz to 7 dB at 38.5 GHz in a down-conversion mode, when the PIN-PD bias voltage was 0 V. The conversion gain degrades with the decrease of the bias voltage from 0 to −5 V. Error vector magnitudes (EVMs) of the quadratic amplitude modulation (M-QAM) up and down-converted signals are investigated. Quadrature phase shift keying (QPSK) data at bit rates between 312.5 Mbit∕s and 5 Gbit∕s are frequency-converted. The EVM is used a performance index to assess the mixing system. Exploitable EVMs in the range of 15% up to 34.9% are reached for up-conversion of the mixing frequency. For down-conversion, the EVM varies from 20% to 34.9% at 5 Gbit∕s over the whole frequency range. The EVM of mixed signals is improved with 16-QAM and 64-QAM modulations.