Research And Design Of ?? Modulator Applied To SDoF Systeam

Radio over Fiber technology,which combines wireless communication technology and optical fiber communication technology,is very suitable for modern communications that are developing towards high bandwidth,high rate,and high performance.Compared with the relatively mature Analog Radio over Fiber system and Digital Radio over Fiber system,the Sigma Delta over Fiber system has the same transmission distance and dynamic range as the DRoF system under the premise of reducing system complexity and cost,and this advantage comes from the high-speed and high-precision ?? modulator.Therefore,studying the ?? modulator of the SDoF system has great application value.The wideband ?? modulator of the SDoF system requires single-bit quantization.This article first analyzes the principle and structure of the single-bit ?? modulator in detail,and discusses the non-ideal factors in the ?? modulator based on the active integrator through modeling on smulink.After synthesizing the modeling results,system specifications and design difficulty,This design finally selects a 3rd-order passive continuous-time ?? modulator scheme that can get rid of the bandwidth limitation of the op amp to the ?? modulator.The passive loop filter is optimized by genetic algorithm,and the output signal-to-noise ratio of the modulator model simulation is 55dB.The average output signal-to-noise ratio of the Monte Carlo simulation of the modulator model is 47.8dB,and the variance is 2.75dB,indicating that the designed passive filter can resist the influence of the deviation of the passive device.The minimum resolution voltage of the designed three-stage structure comparator can reach 5mV,and the output delay is 42pS.The feedback current steering DAC uses a complementary fully differential structure to reduce the influence of inter-symbol interference.At the same time,the switch driving circuit of the current steering DAC is designed to reduce the output swing of the switch signal from 1.1V to 600mV,and the signal cross point is set in 450mV,which reduces the output delay and glitch of the DAC.The excess loop delay of the modulator is compensated by referring to the PI-element compensation method.Then this paper completes the circuit design of a single-bit quantized wideband ?? modulator based on TSMC 40nm CMOS process.The previous simulation results show that the bandwidth of the designed ?? modulator based on a passive filter can reach 100 MHz,which works at 10GHz,and its output signal-to-noise ratio is 52.29 dB,which corresponds to an effective accuracy of 8.39 bits,and the power consumption of modulator is 22mW.Finally,the modulator is drawn and postsimulated.Compared with the previous simulation,the output signal-to-noise ratio of the modulator drops to 28.93dB,and the effective number of bits drops to 4.56bits.At the end of the thesis,the circuit and layout of the module replace the simulation method to analyze and prove the key problems that lead to the decrease in accuracy.And the solutions are given,which point out the direction for improving the performance of the ?? modulator.