ADC、DAC选型与匹配电路设计课件

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,ADC,、,DAC,选型与匹配电路设计,目录,DAC,评估环境,DAC,选型关键指标,AQM,匹配设计,DAC,使用外部高频时钟的优点,DAC,与,IQ,调制器配合校准本振泄露与镜像,IQ,调制器最大输出功率、噪声系数与,ACPR,计算,DAC,与,IQ,调制器之间的低通滤波器设计,ADC,评估环境,ADC,等效噪声系数计算,ADC,采样时钟的要求与中频的选择,时钟抖动对,ADC SNR,的影响,相噪与时钟抖动的转换,ADC,前端驱动电路设计,ADC,满量程均值功率计算,ADC SFDR,、,SNR,、,IM3,要求,测试灵敏度时通道最小增益要求,测试阻塞信号时通道最大增益要求,DAC,评估环境,DAC,关键指标,DAC,关键指标,底噪与,SFDR,分析：,底噪,以,WCDMA,为例，,3GPP,协议对系统带外杂散的要求是,-30dBm/1MHz,。,IQ,调制器的输出为,-15dBm,，功放输出为,46dBm,（,40W,），那么整个下行系统的增益为,46 - (-15) = 61dB,。,为了满足协议的要求那么,DAC,的底噪水平要低于,-30 61 -10lg(1M) = -151dBM/Hz,。,SFDR,AD9148 SFDR,为,65,。,IQ,调制器的输出为,-15dBm,，下行总增益为,61dB,，那么杂散水平,= -15 + 61 65 = - 19dBm/3.84M = -24.84 dBm/1MHz,，需要介质滤波器或腔体滤波器提供,6dB,的带外抑制。,DAC,关键指标,ACLR,与,IMD3,分析：,ACLR,在,PLL OFF,的状态下,AD9148,的,ACLR,为,-79,。,4,载波则是,-73,。,带外杂散的要求是,-30dBm/1MHz=-24.16dBm/3.84MHz,。对应于,46dBm,的功放输出则是,ACLR=70.16dBc/3.84MHz,。因此要求,ACLR,大于,70,。,IMD,AD9148,的,IMD,为,76,，对应于单载波的,ACLR,则是,-(76 + 3) = -79,，与数据手册给出的相符。,在,DAC,底噪不受限制时，,IMD,值可以简单的估算为是单载波,-,（,ACLR+3,）。,DAC,使用外部高频时钟的优点,1.DAC,输出信号的量化噪声更低,DAC,输出信号的噪底,= DAC,本身的噪声,+,采样时钟的远端相噪,- 10lg(,外部高频时钟频率,/DAC,输出信号频率）,2.DAC,输出信号相对采样时钟的镜像更远,镜像频率,=,外部高频时钟频率,- DAC,输出信号频率,DAC,输出,SINC,函数对镜像的衰减更大,DAC,与,IQ,调制器配合校准本振泄露与镜像,1.DAC,通过调整,I,路与,Q,路直流偏置（,DC OFFSET,）的方式来抑制本振泄露。,此方法目前有很大的局限性，当本振频率变更或温度变化较大时，抑制度会明显恶化。,2.DAC,通过调整相位与,I,、,Q,两路幅度的方式来抑制镜像。,此方法很稳定，抑制度不会随着本振频率的变更或温度的变化而明显恶化。,AQM,匹配,Setup,R1ohm,39,R2ohm,340,R3ohm,1200,R4ohm,576,IFSmA,20,V2V,5.00,V1V,0.00,DAC,DAC R,36.51,DAC Common Voltage,0.50,MOD,DAC Swing(Single),0.73,Modulatorcommon voltage,1.50,Mod Input Swing Single,0.30,Loss by R2Db,-7.83,AQM,匹配,1.R4 = 2*(R1+R2)|R3,2.DACR = (0.5*R4)|R3+R2|R1,3.VDAC = V2*R1/(R1+R2+R3) + 0.5*IFS*R1|(R2 + R3),4.DAC Swing = IFS* DACR,5.VMod = V2*(R1+R2)/(R1+R2+R3) + 0.5*IFS*R1*R3/(R1+R2+R3),6.Mod Input Swing = (DAC Swing)*R3|(0.5*R4)/R2 + R3|(0.5*R4),7.LOSS = 20lg(DAC,Swing/Mod Input Swing,),IQ,调制器最大输出功率、噪声系数与,ACPR,计算,1.IQ,调制器输入信号,Vpp = 1V,电压增益,= -3dB,输出阻抗,= 50,欧姆,Pout = 10lg(0.5*1*0.5)2*1000/50/2= -0.2dBm,2.IQ,调制器芯片底噪为,-159dBm/Hz,，热噪声,= -174dBm/Hz,NF = -159 - (-174) = 15,3.IQ,调制器,OIP3 = Pout + 0.5*IMD = 25dBm,，输出信号功率,= -15dBm,最大非线性产物,= -15 - 2*,（,15 + 25,）,= -95dBm,4.DAC,输出信号的总底噪,= -159dBm/Hz, WCDMA,单载波带宽,=3.84M,IQ,调制器输出信号总底噪,= -159 + (-159) + 10lg3.84M = -90dBm/3.84M,5.IQ,调制器输出信号的,ACPR =(-95) - (-90) - (-15) = -73.8dBm/3.84M,AQM LC,滤波器设计,AQM LC,滤波器设计,AQM LC,滤波器设计,ADC,评估环境,ADC,评估环境,ADC,等效噪声系数计算,RX ADC NF analysis,LOG or F,ADC SNRFS,78,FS POWER,4,ADC SNR,74,SNR BW,20000000,ADC NOSE1Hz,-147.01,KTB,-174,ADC NF,26.9897,ADC,的噪声密度,-78 + 4 10lg20M = -147dBm/Hz,ADC,的噪声系数,-147 -,（,-174,）,= 27,ADC,采样时钟的要求与中频的选择,1.,反馈通道采样时钟必须满足,DPD,算法所需的带宽。,20M LTE,信号，,DPD,算法需,5,阶互调产物，那么采样时钟,Fs20M*5*2 = 200MHz,2.,带通采样中频,IF = Fs*(2n + 1)/4,时钟抖动对,ADC SNR,的影响,1. ADC,孔径不确定性,= 200FS,，采样时钟抖动,= 400FS,总时钟抖动,= sqrt(2002 + 4002) = 447FS,2. ADC,的输入信号频率,=140MHz,SNRmax = -20lg2*140M*447FS= 68,相噪与时钟抖动的转换,ADC,前端匹配电路,ADC,满量程均值功率计算,匹配电阻为,200,欧姆，输入信号,Vpp=2V,。,PFs = 10lg(2/2)2/200/2*1000 = +4dBm,匹配电阻为,50,欧姆，输入信号,Vpp=2V,。,PFs = 10lg(2/2)2/50/2*1000 = +10dBm,ADC SFDR,要求,WCDMA,带内最大阻塞信号是,-40dBm3.84Mhz,，有用信号为,-115dBm,，处理增益,=25dB,，解调门限,=6,，热噪声,=-174,1.3.84M,热噪声,= -174 + 10lg3.84M = -108.1dBm/3.84MHz,2.,最大可接受噪声,= -115 + 25 - 6 =-96dBm/3.84MHz,3.,除去热噪声后可接受的干扰信号,= -96 - (-108.1) = -96.3dBm/3.84MHz,4.SFDRin= -40 -,（,-96.3,）,= 56.3dBc,5.SFDRex= -15 -,（,-96.3,）,= 81.3dBc,ADC SNR,要求,输入信号的底噪需要比,ADC,底噪大,10dB,，,WCDMA,带内最大阻塞信号是,-40dBm3.84Mhz,，灵敏度要求,= -121dBm,，处理增益,=25dB,，解调门限,=6,。,1.,最大可接受噪声,= -121 + 25 -6 = -102dBm/3.84MHz,2.,动态范围,= -40 -,（,-102,）,= 62dB,3.PAR= 7dB,，通道不平坦度,3dB, ADC,底噪需比输入信号噪声低,10dB,SNRFS 62 + 7 + 3 + 10 = 82dBFS/3.84MHz,4.ADC,采样速率,=184.32MHz,奈奎斯特域内的,SNRFS = 68,SNRFS = 68 + 10lg(184.32/2/3.84) = 82dBFS/3.84MHz,5.ADC SNRBOOST,或,NSR,带宽,=40M,，带宽内,SNRFS = 76,SNRFS = 76 + 10lg,（,40/3.84,）,= 86dBFS/3.84MHz,ADC IM3,要求,双音互调,-47dBm,，在互调测试时接收机系统噪声系数,NF=5,。,1.3.84M,热噪声,= -174 + 10lg3.84M +5 = -103.1dBm/3.84MHz,2.,最大可接受噪声,= -115 + 25 - 6 =-96dBm/3.84MHz,3.,除去热噪声后可接受的干扰信号,= -96 - (-103.1) = -97dBm/3.84MHz,分配到每音调,-97 -3 = -100dBm/3.84MHz,4.ADC,的满量程功率,= +4dBm,，,RRU,上行通道增益调整后为,40dB,。,ADC,底噪,=-100 + 40 = -60dBm,进入,ADC,的互调信号功率,= -47 + 40 = -7dBm = -11dBmFS,5.IM3FS = 4 - (-60) = 64dBFS,IM3 = -7 - (-60) = 53dB,测试灵敏度时通道最小增益要求,WCDMA,灵敏度要求,= -121dBm,，处理增益,=25dB,，解调门限,=6,。,1.,最大可接受噪声,= -121 + 25 -6 = -102dBm/3.84MHz,2.ADC SNRFS = 68,，采样速率,= 184.32MHz,，满量程功率,=+4dBm,ADC,底噪,= -(68 - 4) - 10lg(184.32/2/3.84) = -77.8dBm/3.84MHz,3.,考虑到,ADC,底噪需比输入信号噪声低,10dB,与通道不平坦度,3dB,上行通道总增益,-77.8 + 10 + 3 - (-102) = 37.2dB,测试阻塞信号时通道最大增益要求,WCDMA,带内最大阻塞信号是,-40dBm3.84Mhz, ADC,满量程均值功率,= +4dBmFS,，信号,PAR= 7dB,，通道不平坦度,3dB,上行通道总增益,4 - 7 - 3 -,（,-40,）,= 34dB,附件,Thank you for listening,