Highly Accurate Dual-Band Cellular Field Potential Acquisition For Brain–Machine Interface

Abstract

Cellular field potential includes local field potential (LFP, 0.1 Hz–200 Hz) and spike potential (SP, 200 Hz–10 kHz). In physiological studies of the brain, SP signal has been the focus. Various circuits have been reported to acquire SP signals in brain–machine interface (BMI) systems over the years. Recent study shows that the LFP signal plays important roles in modulating many profound neuronal mechanisms in the brain. It is important for new BMI design to record the dual-band signal accurately, which demands acquisition circuits to have low noise and good linearity in both bands. In this paper, we report the design of a dual-band acquisition integrated circuit (IC) for microelectrode recording. The novel design uses a continuous- time (CT) front-end with chopping to suppress the noise, and a discrete-time (DT) back-end to achieve good linearity. A prototype monolithic acquisition IC is fabricated in a 0.35 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm m}$</tex></formula> CMOS process. It has 16 acquisition channels and an 11 bit successive-approximation (SAR) analog-to-digital converter (ADC). Silicon measurements show that every channel has <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$29.2\,{\rm nV}/{\rm Hz}^{0.5}$</tex></formula> noise and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&lt;}0.1\%$</tex></formula> nonlinearity. The good linearity effectively prevents the aliasing and mixing between the two bands. For LFP signals, the recording noise is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$0.9\,{\mu}{\rm V}_{\rm rms}$</tex></formula> . For SP signals, the recording noise is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$2.9\,{\mu}{\rm V}_{\rm rms}$</tex></formula> . Important to the microelectrode recording, the new design has high input impedance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(320~{\rm M}\Omega$</tex></formula> at <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$1\,{\rm kHz})$</tex></formula> , high common-mode rejection ratio (CMRR) <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({&gt; 110}~{\rm dB})$</tex></formula> and power-supply rejection ratio (PSRR) <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$({&gt; 110}~{\rm dB})$</tex></formula> . Noise-efficiency factor (NEF) of the acquisition channel is 6.6. The IC is experimented with rat cardio-myocytes recording.