Design of High-Precision Complex Quadrature Modulators and Demodulators

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Because quadrature amplitude modulation (QAM) is applied to WLANs and cellular systems to obtain higher bit rates, an error vector magnitude (EVM) with less than 1% is strongly demanded. We can express local oscillator (LO) signals with phase and amplitude impairments in the complex signal domain. In a quadrature modulator, the negative-frequency component of the LO signal is an undesired one. Therefore, using a complex quadrature modulator and a complex filter, we can reduce an undesired radio frequency (RF) signal. Moreover, introducing a new LO-phase-error correction circuit, we can get EVMs of less than 1%. This modulator dissipates only 8.2 mW at a 1.2-V-power supply.