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.

Integrated Sensing and Communication (ISAC) represents an innovative paradigm for enhancing spectrum and hardware utilization for both sensing and communication. A specific type of ISAC, radar backscatter communication, involves low-power nodes embedding data onto radar signal reflections rather than generating new signals. However, existing radar backscatter techniques only facilitate uplink communication from the tag to the radar, neglecting downlink communication. This paper introduces BiScatter, an integrated radar backscatter communication and sensing system that enables simultaneous uplink and downlink backscatter communication, radar sensing, and backscatter localization. This is achieved through the design of chirp-slope-shift-keying modulation on top of Frequency Modulated Continuous Wave (FMCW) radars, complemented by passive differential circuitry at the backscatter tags for low-power decoding. BiScatter also presents a packet structure compatible with off-the-shelf radars that offer accurate data processing and synchronization between radar and tag. We prototype this backscatter network in both 9GHz and 24GHz, demonstrating its capability to extend across different frequency bands. Our evaluations demonstrate that BiScatter supports two-way backscatter communication with BER lower than 10-3 up to 7m range and centimeter-level tag localization accuracy on top of off-the-shelf FMCW radars. The presented approach significantly augments the versatility and efficiency of ISAC for low-power devices.