The design and implementation of an X-band phase shifter MMIC using the standard 0.18-m CMOS process is presented. A transformed doublet varactor load is analyzed and applied to a 3-dB
INTRODUCTIONMonolithic continuous phase shifters are of great importance in multiple-antenna transceivers for wireless communication systems [1, 2]. In these systems, the antenna beams are dynamically controlled by changing the phase and magnitude of RF signal fed to each antenna element, based on the channel quality estimation in base-band. Different phase shifter topologies have been reported, in which the passive reflection-type topology provides advantages of high linearity, low noise figure, simple control, and zero power consumption. Numerous monolithic passive reflection-type phase shifters in GaAsbased technology have demonstrated significant performance [3][4][5].By considering the growing demand of single-chip integration of RF transceiver with base-band circuits, it is desirable to have high-performance phase shifter MMIC in silicon-based technology. The work in [1], using 0.25-m SiGe BiCMOS technology, has an insertion loss of 8.1 Ϯ 1.9 dB over the 85°phase shift tuning range in 9.7-11 GHz. A 0.18-m CMOS phase shifter MMIC, reported in [2], has an insertion loss of 10.0 Ϯ 4.0 dB over were used to reduce the insertion loss to an averaged 7.8 dB over the 105°phase shift tuning range in 2.27-2.45 GHz at the expense of 1.8-mW power consumption. However, the insertion-loss variation is Ϯ3.2 dB, which is still wide and induces large phase-modulation to amplitude-modulation distortion.In this letter, we propose an enhanced CMOS passive reflection-type phase shifter by using a transformed doublet varactor load to reduce the average insertion loss as well as to minimize the insertion-loss variation over a phase shift tuning range greater than 180°in X-band, while the advantages of compact size and zero power consumption are still reserved. Figure 1 depicts the circuit topology of the proposed X-band CMOS reflection-type phase shifter MMIC, which is composed of a 3-dB quadrature coupler [6 -8] and two transformed doublet varactor loads. The transmission-line prototype of the doublet varactor load is shown in Figure 2(a), where we can obtain the reflection coefficient at operating frequency o as
CIRCUIT DESIGNThe squared term in Eq. (1) implies a double phase shift tuning range of a single load Z L with respect to a reference port impedance of 2Z o . By replacing the /4 transmission line with the lump -model and assigning the Z L as a parallel-resonant circuit of a varactor diode and an inductance of 2Z o / o , as shown in Figure 2(b), the reflective load could be simplified to the proposed doublet varactor load with an interconnecting inductance L eq ϭ 2Z o / o , and the reflection coefficient can be rederived as where C v denotes for the voltage-controlled capacitance of the varactor. In Eq. (2), the phase shift tuning range can be found aswhere C vo ϭ (C v,max C v,min ) 1/2 and r c ϭ C v,max /C v,min represent the ...
