Feedback lock-in: A versatile multi-terminal measurement system for electrical transport devices

Abstract

We present the design and implementation of a measurement system that enables parallel drive and detection of small currents and voltages at numerous electrical contacts to a multi-terminal electrical device. This system, which we term a feedback lock-in, combines digital control-loop feedback with software-defined lock-in measurements to dynamically source currents and measure small, pre-amplified potentials. The effective input impedance of each current/voltage probe can be set via software, permitting any given contact to behave as an open-circuit voltage lead or as a virtually grounded current source/sink. This enables programmatic switching of measurement configurations and permits measurement of currents at multiple drain contacts without the use of current preamplifiers. Our 32-channel implementation relies on commercially available digital input/output boards, home-built voltage preamplifiers, and custom open-source software. With our feedback lock-in, we demonstrate differential measurement sensitivity comparable to a widely used commercially available lock-in amplifier and perform efficient multi-terminal electrical transport measurements on twisted bilayer graphene and SrTiO3 quantum point contacts. The feedback lock-in also enables a new style of measurement using multiple current probes, which we demonstrate on a ballistic graphene device.

Research progress of lock-in amplifiers

“…中, 用于研究电荷输运、化学传质、离子迁移、界面 充放电等过程规律 [7] . 交流阻抗是锁相放大器的一个主要应用方向, 尽管锁相放大器与精密电桥等部件已经被集成在 专门的阻抗分析仪中, 锁相放大器用户在没有阻抗 分析仪的情况下, 除了可以通过增加电桥电路来替 代阻抗分析仪的功能, 还能够在应用锁相放大器与 电桥的组合过程中完成普通的阻抗分析仪不能实 现的阻抗测量, 比如通过极小驱动电流精细测量易 烧损器件 [67] 、在短时间内用较大电流来测量微欧 姆及以下电阻 [68] 、实时反馈补偿与快速成像等 [69] .…”

“…电池内阻测量, 锁相放大器 技术被应用于储能电池健康监测应用, 能有效提高 微弱信号检测中的信噪比和分辨率, 邓荣与江国栋 [70] 运用锁相放大器结合交流比例法, 实现蓄电池内阻 的精确测量(电阻分辨率达17 μΩ), 还可以对运行 中的电动汽车电池进行精密的在线监测管理 [71] ; 生物阻抗分析 [72,73] ; 纳米孔阻抗分析 [74] ; 超导电阻 测量中, 交流I-V测量的是直流I-V曲线的一阶导 数, 反应微分导纳或阻抗性质, 通过交直流耦合器 件, 可以改变或扫描直流偏压来测量微分阻抗随偏 压的变化曲线, 进而得到比直流电阻测量结果更精 确的I-V曲线 [75] . 此外, 为了获得纳欧姆级别低损 耗元件的准确测量, 除了使用无感电阻进行电流监 测外, 往往还需要进行原位相位补偿 [68] ; 精密电容 检测, 如意大利米兰技术学院的Carminati [76] 通 过CMOS超低噪声和宽带电流传感电路耦合到锁 相放大器, 在1 MHz范围内进行精密阻抗测量, 在…”

“…不过, 对 emu emu的磁矩测量 [84] . 图 12 运用锁相放大器进行阻抗测量的几种典型场景电路 (a)电池内阻测量 [70] ; (b)生物电阻抗在微流控中监测运动 [72] ; (c)超 导电阻测量 [68] ; (d)精密电容监控 [76] Fig. 12.…”

“…12. Several typical application scenes with circuits for impedance measurement using Lock-in amplifier: (a) Battery internal resistance measurement [70] ; (b) bioimpedance for movement monitoring in microfluidic channels [72] ; (c) superconducting resistance measurement [68] ; (d) precision capacitor monitoring [76] .…”