Large capacitances are needed for low-frequency active filters to process biomedical signals. The large capacitance can be implemented on a chip by an impedance scaling circuit. However, the characteristics of the circuit are affected by process variations. Then, we have proposed a digitally programmable impedance scaling circuit using electrical switches to compensate for the process variations. This paper describes a technique to reduce power consumption as compared with the conventional circuit. The proposed circuit is composed of a three-stage current mirror circuit and electrical switches. To reduce the power consumption, the only signal current is amplified by current mirror circuits and bias current sources. The tuning range of the scaling factor of capacitance is from −35% to +28%, and the tuning accuracy is 1% using six switches. The validity of the proposed method is confirmed by simulations using HSPICE. The power consumption of the proposed circuit is reduced by 51% as compared with the conventional circuit. The proposed circuit is applied to a filter whose cutoff frequency is 100 Hz. From the tuning result, the tuning error is less than 1% for ±30% of ±3σ global variation and ± 3% of ±3σ local variation. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

中文翻译：

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一种三级可编程阻抗缩放电路

低频有源滤波器需要大电容来处理生物医学信号。大电容可以通过阻抗缩放电路在芯片上实现。然而，电路的特性会受到工艺变化的影响。然后，我们提出了一种数字可编程阻抗缩放电路，使用电气开关来补偿工艺变化。本文描述了一种与传统电路相比降低功耗的技术。所提出的电路由三级电流镜电路和电气开关组成。为了降低功耗，唯一的信号电流被电流镜电路和偏置电流源放大。电容缩放因子的调谐范围为-35%至+28%，使用六个开关的调谐精度为1%。所提出方法的有效性通过使用 HSPICE 的仿真得到证实。与传统电路相比，该电路的功耗降低了 51%。所提出的电路应用于截止频率为 100 Hz 的滤波器。从调谐结果来看，±3的±30%的调谐误差小于1%σ全局变异和 ±3 σ局部变异的± 3% 。© 2021 日本电气工程师学会。由 Wiley Periodicals LLC 出版。