A 5-Gb/s 2.1–2.2-GHz Bandpass \'44elta \'53igma Modulator for Switch-Mode Power Amplifier
P. Ostrovskyy, H. Gustat, M. Ortmanns, C. Scheytt, Microwave Theory and Techniques, IEEE Transactions On 60 (2012) 2524–2531.