A Feedback-Controlled Technique with High Impedance and High Linearity for Neural Signal Applications

A high impedance path with linear DC and frequency response is critical in neural signal applications, such as biasing the neural signal to protect the living cells against overheating, increasing the feedback gain and forming a very large time constant cut-off frequency of a filter. When in integrated circuit (IC) form, pseudo resistors (PR) yield a large resistance within an acceptable die area. However, its linearity is limited by the nonlinear MOS transistors in weak inversion. The linearity can be improved by utilizing a voltage buffer. However, the impedance of the voltage buffer is limited by the output resistance of the amplifier. In this paper, a feedback-controlled technique targeting neural signal applications is proposed. It substantially employs a high impedance, and provides an enhanced linearity with a wide frequency range.