This paper presents the analysis and design of a passive front-end (PFE) for low-power receivers. The freedom of the antenna impedance is observed and exploited to propose an inductive-antenna-based PFE. Analytical methods for the desired signal transfer and noise behavior of the proposed PFE are presented to offer insight into the proposed technique and facilitate the design. The analysis suggests that the inductive-antenna-based PFE offers higher voltage gain and lower noise figure than a standard 50 Ω-based PFE does, which is confirmed by simulations. The proposed PFE and a baseband bandpass amplifier are designed in 0.18-μm CMOS technology for the 402-405 MHz band of the IEEE 802.15.6 WBAN standard. Their combination exhibits a passive voltage gain of 11.6 dB, a NF of 14.7 dB, and an in-band IIP3 of 3.6 dBm, while dissipating 1.1 mW from a 1.2 V supply.

Simultaneous measurement of Electrocardiogram (ECG) and bio-impedance (BioZ) via disposable health patches is desired for patients suffering from chronic cardiovascular and respiratory diseases. However, a sensing IC must consume ultra-low power under a sub-volt supply to comply with miniaturized and disposable batteries. This work presents a 0.6 V analog frontend (AFE) IC consisting of an instrumentation amplifier (IA), a current source (CS) and a SAR ADC. The AFE can measure ECG and BioZ simultaneously with a single IA by employing an orthogonal chopping scheme. To ensure the IA can tolerate up to 300mVpp DC electrode offset and 400mV _pp common-mode (CM) interference, a DC-servo loop (DSL) combined with a common-mode feedforward (CMFF) loop is employed. A buffer-assisted scheme boosts the IA's input impedance by 7x to 140MΩ at 10Hz. To improve the BioZ sensitivity, the CG utilizes dynamic element matching to reduce the 1/f noise of the output current, leading to 35mΩ/√Hz BioZ sensitivity down to 1Hz. The ADC shows a 9.7b ENOB when sampled at 20ksps. The total power consumption of the AFE is 3.8μW.