1 MHz Modulation Frequency 28 nm CMOS 1ng Sensitivity Analog Front-End for Nanogravity Accelerometers in Aerospace Applications

Accelerometers in microgravity environments are stimulated by very weak (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{nm} / \mathrm{s} 2$</tex>) and very low frequency (< 1 Hz) accelerations, which are therefore very difficult to detect. Thus, the signal processing chain driven by the accelerometer operates at frequencies higher than the band of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1 / \mathrm{f}$</tex> noise as in classical amplification stages. For these reasons the state-of-the-art solutions are often based on analog continuous-time Mixers adopting specific technological choices such as: electrical off-the-shelf transformers directly coupled to the accelerometer and almost flicker-free junction/bipolar Transistors Low Noise Amplifiers. Obviously, this approach severely limits the possibility of miniaturizing analog front-ends disabling the scaling down of the electronic silicon integrated systems. This paper definitively solves the previous problems, proposing a signal processing technique that allows the integration of the front-end in nmrange scaled-down technologies (28 nm CMOS). Specifically, this article focuses on design and development of an analog frontend system composed of an Accelerometer, a (passive) Mixer and a Low Noise Amplifier that allows the reconstruction of signals of the order of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10 \text{nm} / \mathrm{s}^{2}$</tex> on bands of the order of a few Hz. The proposed Nanogravity Accelerometer Analog Front-End (nG-AFE) exhibits 53 dB gain (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{nm} / \mathrm{s}^{2}$</tex> to V) at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&lt;1 \text{nm} / \mathrm{s}^{2} / \sqrt{\text{Hz}}$</tex> Equivalent acceleration noise Power Spectral Density, performing a final (after digital signal processing reconstruction) 23.5 dB Signal-to-Noise Ratio at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1 0 n m / \mathbf{s}^{\mathbf{2}}$</tex> minimum input acceleration.