A 38.4 nW, 1.2 V, 250-Hz, 2^nd-Order g_m – C LPF With Degenerative SCP Transconductors Achieving 800-mV_PP Input Range and 82.1- μV_rms IRN for ECG Acquisition

In this brief, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2{^{\text {nd}}}$ </tex-math></inline-formula> -order <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g_{\mathrm { m}} - C$ </tex-math></inline-formula> lowpass filter with a practical input linear range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400~{\mathrm { mV}}_{\mathrm { P}}$ </tex-math></inline-formula> dedicated to ECG signal acquisition is proposed. This filter employs a degenerative source-coupled-pair circuit as a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g_{\mathrm { m}}$ </tex-math></inline-formula> cell. It enhances the linear input range by a factor of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 4$ </tex-math></inline-formula> compared with the source follower filter. Additionally, to mitigate the effect of current source mismatch, a dynamic element matching technique is applied. By doing so, HD2 is suppressed more than 1.5 dB over the entire passband frequency. This proposed filter is implemented in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18~\mu $ </tex-math></inline-formula> m CMOS process. It offers a 250-Hz bandwidth with input-referred noise and a dynamic range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$82.1~\mu {\mathrm { V}}_{\mathrm {\mathrm {rms}}}$ </tex-math></inline-formula> and 67.34 dB, respectively. The power consumption of 38.4 nW is achieved with a 1.2 V supply. Compared with other recent nano-power filters, the proposed filter provides the highest linear input range with competitive Figure-of-Merit to the top-tier designs. It is therefore beneficial to the practical implementation of a low-power ECG acquisition system.