1 Abstract - A 2.4-GHz half-sine shaping O-QPSK transmitter (TX) which supports IEEE 802.15.4 standard is reported. This TX employs a RF phase modulator which incorporates a semi-digital FIR filter for waveform shaping. Fabricated in a 0.18- m CMOS process, the TX, including a PLL, draws 10 mA from a 1.5-V supply and delivers an output power of -3 dBm. It achieves an EVM of 6.2% when operating at 2-Mcps chip rate. I. INTRODUCTION The IEEE 802.15.4, an emerging low-power wireless standard, is established to address the short-range low data rate, wireless sensor network applications. It supports operation at multiple frequency bands; each with different modulation format. For the 2.4GHz band, the half-sine shaping offset-QPSK (HS-OQPSK) modulation scheme is adopted with a chip rate of 2Mchip/s. VCO PFD/CP/LF f REF N MOD Equalizer PA Tx Output Digital MOD. TXData TXCLK PLL-based Tx (a) Poly-Phase Generator PA P0 P180 P90 P270 Digital MOD. I-DAC Q-DAC I-Filter Q-Filter I Q TXData TX CLK Mixer-based Tx Tx Output IQ mixer f REF (b) Fig. 1 Conventional TX architectures. (a) The PLL-based TX. (b) The mixer-based TX. A HS-OQPSK TX can be implemented with the PLL-based architecture [2], as depicted in Fig. 1(a). However, in this TX, the transmission data rate is limited by the PLL bandwidth. To solve this design issue, sophisticated bandwidth extension techniques, e.g. digital equalization or two-point modulation method, are often required to compensate for the loop dynamics and extend the data rate beyond the PLL bandwidth. Still, mismatch error of the compensation path or unbalanced paths degrades the modulation performance. Alternatively, the mixer-based topology, as illustrated in Fig. 1(b), may be employed. In a conventional mixer-based HS-OQPSK TX [3], the waveform shaping is implemented at the digital baseband. The TX is comprised of several analog circuits, such as DACs, filters, gain stages, quadrature mixers. These circuits are susceptible to various analog imperfections and PVT variations. Complex design techniques and higher bias currents are often required to realize a high-performance TX. Furthermore, higher transmission data/chip rate demands wider analog circuit bandwidth, which leads to increased TX power consumption. Several prior IEEE 802.15.4 compliant or WPAN TXs (PLL-based [2] and mixer-based [3] architectures) consume rather high power consumption. In this paper, a digitally-intensive TX architecture employing an FIR-embedded Phase Modulator (FIR-PM) is presented. The proposed TX architecture facilitates a lower power consumption while maintaining good transmission qualities. This paper is organized as follows. Section II introduces the architecture of the proposed HS-OQPSK TX. Section III describes the circuit implementation. Finally, measurement results and conclusion are presented in section IV and V, respectively. II. TRANSMITTER ARCHITECTURE A. Proposed HS-OQPSK TX with FIR-PM Fig. 2 depicts the architecture of the proposed HS-OQPSK TX. Instead of half-sine shaping the data signals at digital baseband, this TX applies waveform filtering directly at RF through the proposed hardware-efficient FIR-PM. The FIR-PM consists of 8 phase selectors (PSs) and an 8-tap FIR filter. The half-sine waveform shaping operation is realized by weighted-summing the selected quadrature phases (P45~P315) through the 8 PSs, where the weighting coefficients are determined by the 8-tap FIR filter. The quadrature phases A 15-mW 2.4-GHz IEEE 802.15.4 Transmitter with a FIR-embedded Phase Modulator Yao-Hong Liu, Hao-Hung Lo, Li-Guang Chen, and Tsung-Hsien Lin Graduate Institute of Electronics Engineering and Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan 978-1-4577-1785-7/11/$26.00 ©2011 IEEE IEEE Asian Solid-State Circuits Conference November 14-16, 2011 / Jeju, Korea