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This work proposes a direct conversion transmitter architecture intended for cognitive radio applications. The architecture is based on the poly-phase multipath technique, which has been shown to cancel out many of the harmonics, sidebands and nonlinearity contributions of a power upconverter using a large number of signal paths. This work proposes a design only using 8 paths which is able to achieve <-40dBc harmonic suppression for all harmonics, including the dominant 7 th and 9 th harmonic. This is done with a combination of duty cycle control of the Local Oscillator (LO) waveform and tunable filtering with only a first order roll-off.

Abstract-Radio transceivers capable of dynamic spectrum access require frequency agile transmitters with a clean output spectrum. High-Q filters are difficult to implement on chip and have limited tuning range. Transmitters with high linearity and broadband harmonic rejection can be more flexible and require less filtering. However, traditional Harmonic Rejection mixers suppress only a few harmonics. This paper presents an 8-path poly-phase transmitter, which exploits mixer-LO duty-cycle control and a tunable first-order RC low-pass filter to suppress ALL harmonics to below -40dBc. The optimum duty-cycle theoretically is 43.65% and a resolution of better than 0.1% is required to keep the spread in harmonic rejection within 1dB.We propose a simple monotonic duty-cycle control circuit and show by design equations and measurements that it achieves the required resolution over 3 octaves of frequency range. Also, analysis indicates that LO duty-cycle reduction compared to 50% improves power upconverter efficiency. A transmitter realized in 0.16m CMOS works from 100-800MHz at a maximum single tone output power of 10.8dBm with an efficiency of 8.7%, outperforming previous designs. The OIP3 is >21dBm, while the LO leakage and image rejection is better than -45dBc.

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