Monitoring the electrical activities of a large number of neurons in vertebrates' central nervous system in vivo through hundreds of parallel channels without interferring in their natural functions is a neuroscientist's interest. Value of this information in both scientific and clinical contexts, especially in expansion of brain–computer interfaces, is extremely significant. Therefore, low-noise amplifiers are needed with filtering capability on the front end to amplify the desired signals and eliminate direct current baseline shifts. Hence, size and power consumption need to be minimized to reduce trauma and heat dissipation, which can result in tissue damage for human applications and the system needs to be implantable and wireless. The practical solution for developing such systems is system-on-a-chip, based on ultra-low-power mixed-mode and wideband RFIC designs. They, however, impose a number of challenges that may require nontraditional solutions. In this paper, we present a fully differential low-power low-noise preamplifier suitable for recording biological signals, from a few mHz up to 10 kHz. This amplifier has a bandpass filter that is tunable between 10 mHz and 10 kHz, and has been designed and simulated in a standard 90-nm CMOS process. The circuit consumes 10 μW from a 1.2 V supply and provides a gain of 40 dB and an output swing of ±0.5 V with a total harmonic distortion of less than 0.5%. The total input-referred noise level is 4.6 μV integrating the noise over 0.01 Hz to 10 kHz.
A design of an ultra low-power operational transconductance amplifier
