This paper presents a 0.36-mm2I2C-to-SPI converter chip with on-the-fly conversion for E-textile applications. The on-the-fly operation eliminates the need for on-chip data buffers and clock generation, improving the area and power efficiency versus prior works. The die area is 7.33× smaller than commercially-available off-the-shelf (COTS) I2Cto-SPI converters, enabling it to integrate unobtrusively into E-textile applications. The chip supports conversion at ultra-fast I2C operating frequency up to 5 MHz while consuming only 0.379 mW of power. At the standard I2C speed of 400 kHz, it consumes 0.145 mW, which is 48× more power-efficient than commercially available I2C-to-SPI converters.

Photoplethysmography (PPG) is a widely adopted technique for monitoring essential physiological parameters like heart rate and blood oxygen saturation (SpO2). The increasing demand for wearable health monitoring devices necessitates the development of energy-efficient PPG systems. This paper proposes an ultra-low power, end-to-end PPG sensing system with continuous monitoring capabilities. The system consists of three distinct chips: a system-on-chip, an analog-front end chip, and a Bluetooth low-energy transmitter, enabling real-time PPG data transmission to a smartphone. All components are fabricated using the bulk 65 nm low-power CMOS process. This system achieves minimal power consumption of 18.78 µW during idle periods and 148.5 µW during active data transmission when aggressively duty-cycled at 2.4%.

This paper presents a 0.36-mm2I2C-to-SPI converter chip designed for electronic textile (E-textile) applications, featuring an on-the-fly conversion scheme that eliminates the need for on-chip data buffers and internal clock generation. By leveraging the synchronous nature of both I2C and SPI protocols, the proposed design forwards each incoming I2C data bit, SDA (Serial Data Line) directly to the SPI output using the I2C serial clock line (SCL), thereby reducing both area and power consumption. Two versions of the chip are proposed: a ‘full’ die and a ‘compact’ die. The converter enables seamless integration into distributed in-textile architectures by minimizing silicon overhead. The ‘full’ die implementation achieves a$7.33\times $area reduction compared to commercially available I2C-to-SPI converters, while the ‘compact’ version further reduces the footprint by$14.73\times $through the use of a small corner seal-ring and a linear pad ring layout. Measurement results confirm robust operation at ultra-fast I2C frequency (5 MHz), consuming only 0.379 mW for the ‘full’ die and 0.333 mW for the ‘compact’ variant. At standard I2C speeds (400 kHz), the converter demonstrates a$48\times $improvement (‘full’ die) in power efficiency over commercial off-the-shelf (COTS) solutions, making it an effective and unobtrusive solution for next-generation E-textile systems.