Finkel A S, Redman S
J Neurosci Methods. 1984 Jun;11(2):101-27. doi: 10.1016/0165-0270(84)90029-3.
The theory of operation of a discontinuous single-electrode voltage clamp using an ideal microelectrode (infinite response speed) and fixed (current-passing) duty cycle has been previously described. In this paper, the theory is extended by considering a microelectrode which has a finite response speed, by allowing the duty cycle to be variable, and by considering the clamp noise. Formulate are derived for the relationships between the step response, the steady-state error, the steady-state ripple, and the stability, in terms of the cycling frequency, the duty cycle, the open loop gain, and the electrical resistance and capacitance of the microelectrode and the cell membrane. In addition, the amplification of the microelectrode noise by aliasing is analysed, the error due to incomplete decay of the microelectrode voltage is described, and the accuracy of averaging the peak current measurement is established. To achieve the fastest dynamic response and the smallest steady-state error, the cycling period should be made as small as possible, and the open-loop gain should be as large as possible, consistent with stability. Incomplete decay of the microelectrode voltage destabilizes the clamp, and can introduce a significant clamp error. The choice of duty cycle is a compromise between reducing the noise and the step response time while avoiding design problems in the current output circuit. The output noise is amplified by aliasing. It can be minimized for a given output filter cutoff frequency by keeping the cycling frequency as high as possible, and by the use of an anti-aliasing filter whose cutoff frequency must be set for each microelectrode.
此前已描述了使用理想微电极（无限响应速度）和固定（电流通过）占空比的不连续单电极电压钳的工作原理。本文通过考虑具有有限响应速度的微电极、允许占空比可变以及考虑钳位噪声来扩展该理论。推导了阶跃响应、稳态误差、稳态纹波和稳定性之间的关系公式，这些公式涉及循环频率、占空比、开环增益以及微电极和细胞膜的电阻与电容。此外，分析了通过混叠对微电极噪声的放大，描述了由于微电极电压不完全衰减导致的误差，并确定了对峰值电流测量进行平均的精度。为了实现最快的动态响应和最小的稳态误差，循环周期应尽可能小，开环增益应尽可能大，同时要保证稳定性。微电极电压的不完全衰减会使钳位不稳定，并可能引入显著的钳位误差。占空比的选择是在降低噪声和阶跃响应时间之间进行权衡，同时避免电流输出电路中的设计问题。输出噪声会通过混叠被放大。对于给定的输出滤波器截止频率，可以通过尽可能提高循环频率以及使用截止频率必须针对每个微电极进行设置的抗混叠滤波器来将其最小化。
