IEEE Access (Jan 2020)
RF Receiver Front-End Employing IIP2-Enhanced 25% Duty-Cycle Quadrature Passive Mixer for Advanced Cellular Applications
Abstract
This paper proposes a second-order input-referred intercept point (IIP2)-enhanced 25% duty-cycle local oscillator (LO) quadrature passive mixer configuration with developing a wideband radio frequency (RF) receiver front-end, suitable for 4G and 5G new radio (NR) sub-6 GHz applications. By combining mixer switches operated by several combinations of quadrature-phase RF and LO signals, the inherent second-order nonlinear characteristics produced by the asymmetric factors of the mixer are greatly improved without any additional calibration process. This second-order linearity improvement is theoretically analyzed in terms of the 25% duty-cycle mixing operations, and is compared to the linearity characteristic observed in the conventional mixer design. To validate the IIP2 performance improvement, a wideband RF receiver front-end with the proposed mixer design is fabricated in a 65-nm CMOS technology. The implemented receiver front-end incorporates a wideband low noise amplifier with a polyphase filter, the proposed quadrature passive mixers, wideband transimpedance amplifiers, and 25% duty-cycle LO circuitry. The performance is characterized mainly in the long-term evolution and 5G NR frequency bands, which range from 1800 MHz to 2700 MHz. The demonstrated design achieves approximately 16 dB higher mean values of the out-of-band (OB) IIP2s compared to a conventional design approach without calibration. The design also attains conversion gains greater than 43 dB, double-sideband noise figures less than 4.4 dB, OB IIP3s greater than -1.52 dBm, and OB input P1dB greater than -23.1 dBm, for all measured frequency bands even in the presence of transmitter blockers. The proposed configuration, excluding the LO circuitry, consumes a bias current of 17.4 mA with a nominal supply of 1.2 V. The active area of the proposed implemented design is 0.6 mm2.
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