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Abstract-Transmitter circuits using large signal swings and hard-switched mixers are power-efficient, but also produce unwanted harmonics and sidebands, which are commonly removed using dedicated filters. This paper presents a polyphase multipath technique to relax or eliminate filters by canceling a multitude of harmonics and sidebands. Using this technique, a wideband and flexible power upconverter with a clean output spectrum is realized in 0.13-m CMOS, aiming at a software-defined radio application. Prototype chips operate from DC to 2.4 GHz with spurs smaller than 40 dBc up to the 17th harmonic (18-path mode) or 5th harmonic (6-path mode) of the transmit frequency, without tuning or calibration. The transmitter delivers 8 mW of power to a 100-load (2.54 V pp-di voltage swing) and the complete chip consumes 228 mW from a 1.2-V supply. It uses no filters, but only digital circuits and mixers.

Dynamic access of unused spectrum via a cognitive radio asks for flexible radio circuits that can work at an arbitrary radio frequency. This article reviews techniques to realize radios without resorting to frequency selective dedicated filters. In particular, a recently proposed polyphase multipath technique canceling harmonics and sidebands is discussed. Using this technique, a wideband and flexible power upconverter with a clean output spectrum has been realized on a CMOS chip, aiming at flexible radio transmitter application. Prototype chips can transmit at an arbitrary frequency between DC and 2.4 GHz. Unwanted harmonics and sidebands are more than 40 dB lower than the desired signal up to the 17th harmonic of the transmit frequency.

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Amplifiers and mixers not only produce a useful amplified or frequency-shifted signal, but also many unwanted harmonics and sidebands caused by nonlinearity and time-variance. Filters are commonly used to clean up the spectrum, but are application specific and often difficult to integrate. Zero-order-hold filtering in a mixer-DAC [2] reduces DAC-related spurs, but does not remove harmonics generated in the mixer. A harmonic-rejection mixer canceling the third-and fifth-order harmonics [3] does relax analog filter requirements. In this paper, we exploit the practical potential of the polyphase multipath circuit theory proposed in [1] to further reduce or even completely eliminate filters by canceling a very large multitude of harmonics and sidebands. As a demonstration, we apply the technique to realize a wideband filter-less power upconverter for possible future multi-standard radio applications in CMOS.

Abstract-Nonlinearity and time-variance in Radio Frequency (RF) circuits leads to unwanted harmonics and intermodulation products, e.g. in power amplifiers and mixers. This paper reviews a recently proposed multipath polyphase circuit technique which can cancel such harmonics and intermodulation products. This will be illustrated using a power upconverter IC as an example. The upconverter works from DC to 2.4 GHz, and the multipath polyphase technique cleans its spectrum up to the 17th harmonic, keeping unwanted spurious responses more than 40dB below the carrier. The technique can also be useful for other applications, and some possible applications will be discussed.

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