New Sensory Method for Neural Activity by Frequency Upconversion With Nonlinear Element

Traditional analog front-ends for biomedical signal acquisitions operate at very low frequencies (Hz-range) and are severely affected by flicker and environmental noise, which degrade the quality of low-frequency signals, thereby reducing the signal-to-noise ratio (SNR). While offering advantages, the increasingly common use of microelectrodes poses challenges due to their low-frequency high impedance, which is comparable to the one of the front-end, thus creating additional difficulties in signal acquisition. To tackle the challenges of in-vitro low-frequency biosignal acquisition, this letter proposes a novel methodology based on the upconversion of low-frequency biosignals to a higher frequency band by a Schottky diode immersed in a solution. This letter aims to demonstrate the feasibility of the new sensory method by translating in frequency the information of a sinewave stimulus representing a biological signal. Experimental results showed a conversion loss of 11.11 dB and demonstrated the upconverted signal propagation in the solution, measuring an intermodulation power above the noise floor, from <tex-math notation="LaTeX">$-$</tex-math> 87.04 to <tex-math notation="LaTeX">$-$</tex-math> 104.13 dBm. The proposed method provides a better signal-to-noise ratio than the traditional acquisition method, estimating an improvement of 8.99 dB.