A highly integrated low-power 2.4GHz transceiver using a direct-conversion diversity receiver in 0.18µm CMOS for IEEE802.15.4 WPAN

Abstract

The IC presented in this paper is a highly integrated low-power RF transceiver for wireless sensor networks (WSN) compliant with the IEEE 802.15.4 2.4GHz WPAN standard. It contains a radio controller with sleep timer and can perform higher-level MAC functions such as beacon detection and network timing synchronisation autonomously, thereby enabling significant power savings in the overall system. The primary design goal for the receive path is to achieve excellent channel selectivity and dynamic range combined with good sensitivity at very low power consumption, all of which are important parameters for the reliable operation of WSN in the harsh 2.4GHz ISM band. The receiver uses a direct-conversion architecture and offers up to 20dB improved interference rejection in the adjacent channels compared to recently published WPAN transceivers based on the low-IF architecture [1,2]. Further emphasizing WSN reliability, the receiver supports switched antenna diversity to mitigate multipath fading. Implemented in a 1P6M 0.18µm RFCMOS process, the IC occupies a die area of less than 5.9mm 2 . It operates with a supply voltage from 1.8V to 3.6V, draws 16.8mA in receive mode and 18mA when transmitting at 3dBm. Figure 24.4.1 shows the chip-level block diagram. The analog, VCO, synthesizer and digital sections are supplied by separate on-chip LDO regulators.Configuration data is retained in a 1.8V backup RAM, which is supplied by an ultra-low-power LDO. The radio controller is based on a power-and area-efficient custom MCU core with optimised instruction set. An amplitude-regulated 26MHz crystal oscillator acts as a calibration reference for the 32kHz RC oscillator. The transceiver is equipped with 2 differential RF ports. The 1 st port is an LNA input only. It has an LNA isolation switch (SW) to attenuate the input signal during the offset correction phase. The 2 nd port is shared between PA and LNA. The transmitter uses direct closed-loop VCO modulation through a fractional-N synthesizer. The bandwidth of the synthesizer is widened with a digital pre-emphasis filter, so that emissions and TX EVM specifications are met simultaneously. The VCO is running at twice the LO frequency to minimise LO self-mixing and pulling effects caused by interferers. The LNA is followed by a passive current-mode quadrature mixer. The input of each transimpedance amplifier (TIA) forms a summing node for the baseband side of the mixer switch pair and 2 current mode DACs which are part of the offset correction loop (OCL).A 3 rd -order 0.25dB-ripple Chebychev filter with 1.3MHz bandwidth attenuates interferers in the ADC sampling image at 13MHz by more than 65dB, and attenuates interferers in the adjacent channel at 5MHz offset by more than 40dB. A 3 rd -order digital IIR filter attenuates signals in the adjacent channel by an additional 35dB while maintaining an overall EVM of less than 5%. The PGA section provides 24dB of gain with 3dB steps and is followed by power-optimised 6b pipeline ADCs. The total voltage gain from antenna to the PGA output...

Trends in low power frontend development for IEEE 802.15.4/ZigBee

“…It is equivalent to Minimum Shift Keying (MSK) and also equivalent to Frequency Shift Keying (FSK) if an appropriate coding step is performed [7]. Due to the application of constant envelop modulation schemas in 802.15.4 a VCO can be directly modulated through a PLL [4] or, alternatively, a mixer in the TX path can be used for frequency up-conversion of the modulated signal [5]. Fig.…”

“…However, some approaches suggest direct modulation of the VCO [4,5] which is very effective because it eliminates the need for the analog TX base band path including the upconverter. As the bandwidth of the IEEE 802.15.4 signal is much higher than the bandwidth of frequency synthesizer, the PLL based direct frequency modulator uses a digital pre-emphasis filter [5] or a twopoint modulator to overcome the bandwidth limitation (see Fig. 2).…”

“…In recent years, a number of papers have been published which use different approaches to obtain optimal radio frontends for 802.15.4 [2]- [5]. This paper gives an overview on the suitable receiver and transmitter concepts and their performance.…”

Efficiency Analysis of Low Power Class-E Power Amplifier

“…If these fully integrated PAs are used in applications requiring low level output power such as wireless body sensor networks, the overall efficiency significantly degrades (Tan, et al, 2012). For example Bluetooth and ZigBee standards are short range standards that their output power level are from 0 to 10 dBm (Retz, et al, 2009;Eo,et al, 2007;Bae, et al, 2011) and in wireless body sensor networks it is even under 0 dBm (Cook, et al, 2006;Tan, et al, 2012). Therefore, high efficiency PA with low level output power is critical to short range wireless sensor network.…”

Power Scalable Radio Receiver Design Based on Signal and Interference Condition

“…Power consumptions in analog and digital portion separately have been reported in some papers. Authors in [10] have reported that baseband of IEEE 802.15.4 consumes 3.2 mA at 1.8 V supply (5.76 mW) in 0.18 µm technology whereas the analog portion consumes 7.0 mA. The authors in [9] have given break up of analog and digital portion of the receiver for UWB.…”