Abstract
This paper presents a 1:2 wideband CMOS balun, and its application for sub-6 GHz wideband front-end. In order to eliminate the amplitude/phase mismatch, the primary and secondary windings are shorted by a transmission line (T-line) for a common ground. The float metal in the primary winding is used for artificial dielectric compensation which further reduce the amplitude imbalance by up to about 0.5 dB. A 2.0-to-3.7 GHz wideband RF front-end is also designed by using the proposed CMOS balun. The balun and RF front-end are fabricated in a 0.13- μm bulk CMOS technology. The bandwidth of the balun with |S11| <; -10 dB is 2.2-to-5.1 GHz. The fractional bandwidth is large than 79.5%. The corresponding maximum amplitude and phase mismatch is 1.5 dB and 2°, respectively. The measured insertion loss is 4.8-to-5.6 dB from 2.2 to 5.1 GHz.
Highlights
Transformer baluns have been widely used in Gilbert mixers, differential amplifiers, phase shifters
This paper presents a 1:2 wideband CMOS balun, and its application for sub-6 GHz wideband front-end
In order to eliminate the amplitude/phase mismatch, the primary and secondary windings are shorted by a transmission line (T-line) for a common ground
Summary
Transformer baluns have been widely used in Gilbert mixers, differential amplifiers, phase shifters. They are typically designed to realize the unbalance-to-balance conversions while keeping a minimum insertion loss, and low amplitude and phase mismatch. An off-chip Marchand balun is modified with a varactor and a series resistor loaded at the central point of the two coupled sections to realize a wide tunable power division ratio and constant phase across 1.2-2.8 GHz band [1]. For sub-6 GHz applications, the coupled spiral transmission lines (T-Line) with the electrical lengths of ~λ/4 in the Marchand balun occupies a large chip area, as shown in [2]. Like other PCB-based designs, the reported balun occupies hundreds of mm area
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