9.5 A 1.2nJ/b 2.4GHz receiver with a sliding-IF phase-to-digital converter for wireless personal/body-area networks

This paper presents an ultra-low-power (ULP) 2.4GHz RX for short-range wireless personal and body-area networks. In such applications, the RF transceiver consumes up to 90% of the total battery energy in a remote sensor node. In order to extend the operation lifetime, it is a primary design goal for such transceivers to improve the energy efficiency, expressed as power consumption/data-rate, to below 1nJ/bit. Although energy-detection or superregenerative ASK RXs [1] are very efficient, they are vulnerable to interference and this leads to a poor quality of the wireless link in a crowded 2.4GHz ISM band. On the other hand, FSK/PSK-type modulations are popular in the target applications because of their power-efficient hardware and higher immunity to interference. They are also widely adopted in many short-range wireless standards like IEEE802.15.4 and Bluetooth Smart. Thanks to the constant-envelope nature of FSK/PSK-type modulations, e.g., HS-OQPSK, they only modulate data on the carrier frequency or phase, so the TX hardware can be simplified, while the efficiency can be enhanced by driving the circuits into a saturated mode, e.g., PLL-based FSK TXs [2,5]. Similarly, in the RX counterpart, instead of processing the signal in the I/Q domain, it can be demodulated in the phase domain by using a phase-ADC [3]. However, such approach still requires a power-hungry high-frequency multi-phase LO generation and “2-dimensional” downconversion and filtering circuits. In the single-channel RX of [4], the VCO is part of the carrier-recovery and phase-demodulation loop. Therefore, the VCO frequency can be easily “pulled away” by an interferer, and the RX has a poor sensitivity because phase noise is deteriorated by the signal chain when input level is low.