Alexandria Engineering Journal (Nov 2024)
A 4-channel neural amplifier employing partial OTA sharing structure with variable gain and bandwidth for implantable neural recording applications
Abstract
Objective: The design of a low-noise low-power 4-channel neural amplifier with variable bandwidth and gain for multi-channel electrode arrays is presented with application in recording of neural signals. Methods: To amplify neural signals with low amplitudes and frequencies, pseudo-resistors are used in the neural amplifier, creating a small low cut-off frequency. The neural amplifier is designed to amplify wide range of neural signals, including Local Field Potential (LFP) and Active Potential (AP) signals, with sufficient gain. In the design process of the proposed amplifier, important parameters such as noise, power consumption, and linearity have been considered and improved to make the proposed structure efficient. The suggested amplifier utilizes an OTA sharing structure where the common parts of amplifiers in distinct channels are shared. The advantage of this structure is that it minimizes the die area and power dissipation of the neural recording system to a significant extent. In addition, the attenuator circuit used in the feedback path can increase the mid-band gain for amplifying low-amplitude neural signals such as LFPs. This avoids the need to increase the value of the input capacitor in order to enhance the mid-band gain, preventing the increase in die area and the decrease in the input impedance of the amplifier. The 4-channel neural amplifier is designed and simulated in 180 nm TSMC CMOS technology. Results: The neural amplifier has a mid-band gain of 47 dB with 3 Hz to 10.8 kHz bandwidth without using an attenuator circuit, and by using the attenuator, the mid-band gain is increased to 55 dB and the bandwidth is decreased to 4 kHz. The power dissipation of each channel is 2.4 µW from 1-V supply voltage. The input-referred noise is 1.9 µVrms over the 3 Hz-10.8 kHz frequency range, and it is 1.45 µVrms over the 11 Hz-4 kHz frequency range when the attenuator circuit is active in the feedback path.
