The Design Of High Speed LVDS Serial Interface Transmitter

Today,with the rapid development of information technology,a substantial increase in the data information,people put forward higher requirement on the rate of information transmission.Because of their technical disadvantage,traditional I/O interface circuit can't meet this demand.In consideration of this situation,a new interface technology is urgently needed to provide higher data transfer rate,and with low noise,low power consumption,low cost advantage.This new technology with high speed,low power consumption,low noise and low cost(LVDS: Low Voltage Differential Signaling)technology brought the possibility to solve this problem.This paper based on the deep research of high-speed interface circuit,design of a high speed LVDS serial interface transmitter circuit.The whole circuit structure includes: LVDS main drive circuit,parallel serial conversion circuit,single ended differential circuit,bandgap reference circuit,voltage-current conversion circuit.LVDS main drive circuit converts CMOS signal into LVDS signal,and provides drive capability for signal transmission.Analyzing and comparing the advantages and disadvantages of LVDS driver's different implementations,select an appropriate circuit structure to design the circuit,use a new common mode feedback circuit,direct regulation of output common mode voltage by feedback voltage,compared with the general indirect adjustment model,this new regulation mode is more direct and effective for the stability of the output common mode voltage.Implementation of parallel serial conversion function includes two parts,in the digital domain,the input of 10 parallel signals through two 5:1MUX circuit,convert to 2 parallel signals,again through 2:1MUX circuit based on CML structure in the analog domain,realize parallel serial conversion,this design avoids the limitations of digital transmission,improve data transfer rate.single ended differential circuit is signal preprocessing circuit for driving circuit,converts the input single ended signal into differential signal.The bandgap reference voltage source and the voltage current conversion circuit are used as the transmitter auxiliary circuit.The bandgap reference voltage is implemented with traditional amplifier clamping,at the same time,the curvature compensation circuit is added to the circuit,realizes low temperature drift of reference voltage source.The reference voltage source provides an accurate reference voltage for the common mode feedback circuit,as a reference value of the output common mode voltage.The voltage to current converter provides a high precision bias current for the drive circuit.Finally,the basic flow of layout design and some general rules that should be paid attention to in the design are introduced,the design of transmitter layout is completed based on TSMC 0.18 CMOS Technology.Using Cadence Spectre simulator,the simulation of each module and the whole transmitter circuit is completed,and the corresponding simulation results are presented.This simulation results indicate that,the reference output voltage is 1.24 V,in the temperature range of-40?to 125?,the temperature coefficient is about 3.02×10-6/?,low temperature drift.The transmitter can correctly achieve the 10 parallel signal to the 1 serial signal conversion,the highest rate can reach 1.25 Gbps,the common mode level of the output LVDS signal is stable at about 1.24 V,differential output swing is 230 mV,meet design requirements.