电容型数字隔离器编解码电路设计

Design of capacitive digital isolator codec circuit

针对电容型数字隔离器在“高速”下的传输可靠性及电流消耗问题,基于台积电(TSMC)180 nm BCD(BipolarCMOSDMOS)工艺设计了一种基于全差分数字隔离器结构的编解码电路.在发送机模块中,输入信号经过施密特触发器进行滤波,三级电流匮乏型环形振荡器产生载波信号.输入信号通过D触发器与载波信号实现时序同步,之后再与载波信号进行混频,混频信号经过驱动电路差分输出.在接收机模块前端设置了前置放大器对衰减后的混频信号进行放大,由NPN和PNP三极管构成的偏置钳位电路给前置放大器提供共模电压,在前置放大器之后连接电平转换模块.解码电路通过RC时间常数将信号频率转化为电压,通过与参考电压的对比,输出解码信号.过程验证测试(PVT)下仿真结果表明,在供电电压为3.3~5 V范围内,可实现25 Mbps最高传输速率,典型传输时延为11 ns.在1 Mbps及25 Mbps传输速率下动态功耗分别为2.1 mA和2.8 mA.在传输速率10 Mbps下输入由线性反馈移位寄存器(Linear Feedback Shift Register,LFSR)产生的随机码序列,均可准确实现编解码功能.说明此设计具有较强的传输可靠性.

Aiming at the transmission reliability and current consumption of the capacitive digital isolator at"high speed",a coding and decoding circuit based on the fully differential digital isolator structure is designed based on the TSMC 180 nm BCD(BipolarCMOSDMOS)process.In the transmitter module,the input signal is filtered by Schmitt flip-flop,and the carrier signal is generated by a three-stage current-deficient ring oscillator.The input signal is synchronized with the carrier signal through the D trigger,and then mix with the carrier signal.The mixing signal is differentially output through the driver circuit.A preamplifier is set at the front end of the receiver module to amplify the decayed mixing signal.A bias clamp circuit composed of NPN and PNP triode provides common-mode voltage to the preamplifier.After the preamplifier,a level conversion module is connected.The decoder circuit converts the signal frequency into voltage by RC time constant,and outputs the decoded signal by comparing it with the reference voltage.The simulation results under Process Verification Test(PVT)show that the maximum transmission rate of 25 Mbps can be achieved and the typical transmission delay is 11 ns when the supply voltage is 3.3-5 V.At the transmission rates of 1 Mbps and 25 Mbps,the dynamic power consumption is 2.1 mA and 2.8 mA respectively.The input random code sequences generated by the Linear Feedback Shift Register(LFSR)can accurately implement the codec function at a transmission rate of 10 Mbps.It shows that this design has strong transmission reliability.