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微分谱测量及锁相放大器

微分谱测量及锁相放大器. 微分谱测量原理. 以 I-V 谱为例, I=f(V) ,怎样测量 d I /d V ? (即 f ’ ) 在 V 中调制入一个小量: V 0 +V m cos t f=f ( V 0 +V m cos t ) = f ( V 0 )+ f ’ ( V 0 ) V m cos t +(1/2) f ” ( V 0 ) V m 2 cos 2 t + …… 因此对于圆频率为  的信号( cos t ),其幅值为:

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微分谱测量及锁相放大器

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  1. 微分谱测量及锁相放大器

  2. 微分谱测量原理 • 以I-V谱为例,I=f(V),怎样测量dI/dV?(即f’) 在V中调制入一个小量:V0+Vmcost f=f(V0+Vmcost) =f(V0)+f’(V0)Vmcost+(1/2)f”(V0)Vm2cos2t+…… 因此对于圆频率为的信号(cost),其幅值为: f’(V0)Vm+(1/8)f’’’(V0)Vm3+……≈f’(V0)Vm∝f’(V0) 所以只要测出对应于圆频率的信号幅度,即能得到信号的微分谱。 • 问题:怎样测量特定频率信号的幅度?? 泰勒展开

  3. 锁相放大器工作原理 关键元件: Phase-sensitive Ditector(PSD) Low-pass Filter(LPF)

  4. PSD(又称为Demodulator、Mixer) 作用是将源信号(vs)与参考信号(vR)相乘: vs=Vscos(st) vR=VRcos(Rt+) voPSD=vs×vR=VsVRcos(st)cos(Rt+) =(1/2)VsVRcos[(s+R)t+] +(1/2)VsVRcos[(s-R)t-] 若s=R,=0,则PSD输出信号的直流部分为(1/2)VsVR∝Vs • LPF 作用是读出PSD输出信号的直流分量。

  5. vs vr voPSD

  6. 锁相放大器只能测量可以被它“放大”的量,并且可以随着被调制量“实时”地变化。(可以不同步)锁相放大器只能测量可以被它“放大”的量,并且可以随着被调制量“实时”地变化。(可以不同步) 如电流、电压、电量等 像“计数”这样的量是不能被锁相放大器测量的 • 用锁相放大器测量俄歇谱的微分谱,所测量的是电流。

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