Design Of GHz Square Wave Signal Generator Based On Phase-locked Loop

Communication security is a basic demand for everyone who uses the Internet.From individuals to countries,they all hope to have completely secure communication.The emergence of quantum communication provides the possibility of absolutely secure communication.Quantum key distribution(QKD)is the most possible branch in the field of quantum communication,and its combination with one-cipher algorithm can achieve absolutely secure communication in theory.In the case of higher and higher communication rate requirements,the working frequency of quantum key distribution system is developing towards the GHz level.A very important factor to determine the working frequency is the driving frequency of the transceiver module,so the research and development of the GHz signal generator is particularly important.However,the realization of GHz signal generator in China is far inferior to that of foreign countries,so the design of GHz signal generator in this paper is of great significance.According to the drive of transceiver module in quantum key distribution system,a PLL based GHz square wave signal generator is designed in this paper.The signal generator has high output bandwidth,and in order to meet the requirements of multiple scenarios,high frequency output channel and low frequency output channel are designed at the same time with delay and amplitude modulation functions.Frequency synthesis method adopts phase-locked loop frequency synthesis technology.In order to realize high precision delay,a method combining high precision programmable delay chip and PLL chip is proposed,which has a wide delay range and high precision.Due to the serious heating of the delay chip,the delay module is equipped with temperature control module based on TEC and PID control technology of semiconductor cooler,which improves the delay accuracy,stability and reliability.For the design of amplitude adjustment function,it is proposed that the drive chip dedicated to high-speed optical communication is applied to amplitude adjustment,and the bandwidth expansion technology is adopted in the drive chip to improve the working bandwidth,which has superior performance in the whole frequency band,and the use of the chip reduces the circuit complexity and the circuit area.Software design to achieve human-computer interaction UI module and IO module two parts.Among them,the human-computer interaction functions realized by UI module include keyboard detection module,LCD display module and LED display.Users set output parameters through the keyboard,get keyboard events from the keyboard detection module,and then get responses from the LCD interface.IO module,which contains the driver module of various chips.In the frequency synthesis module program design,the frequency algorithm of each channel is designed to realize the simultaneous output of multiple channels.In the design of the delay module,the delay algorithm is used to realize the delay function.Amplitude control and temperature control module respectively achieve amplitude adjustment and precision temperature control.This paper implements the output square wave signal,6 independent clock outputs,the operating frequency range of 1 MHz～1 GHz wideband output,the frequency error is within 1%.Two high-speed differential output channels are designed with an output frequency range of 10 MHz to 1 GHz and an output amplitude range of 0.2 to 0.8 V with a continuously adjustable step of 0.1 V.At the same time,in order to meet the diversification of equipment use scenarios and meet other possible needs,four single-ended low-frequency output channels are designed,with an output frequency of 1 MHz to 200 MHz and an output fixed level of LVTTL level.The relative latency accuracy between the six output channels is less than 50ps.