The quadrature modulators and demodulators are widely used to create modern wireless communication systems. It is important to ensure high quality of the transmitted signals in order to have the exchange of information without loss or failure. From the point of view of the spectral decomposition of the signal (Fourier series decomposition), the useful component of the spectrum must be much larger than all other components. The carrier (LO frequency and spurious sideband are the most critical and undesirable quadrature modulator output signal spectral components. In the work, in the course of the research using the methods of suppressing the parasitic components, based on minimizing phase, amplitude and current imbalances in various nodes of the quadrature modulator circuit, have been revealed. In order to realize suppression, the special digital-to-analog converters are used in conjunction with a polyphase filter on varicaps, a phase-shifting block and current sources. The effectiveness of these methods is confirmed by the achievement of suppression of parasitic components in prototypes of 50 dB or more. It has been stated that the phase unbalance minimization is more effective than the amplitude unbalance minimization to sideband suppression. It has been revealed that the use of a phase-shifting block is a more suitable architecture to control the phase unbalance. The obtained results can be useful in the design of high-precision radio frequency units for various purposes.
A tunable Gm-C polyphase filter with high linearity and automatic frequency calibration
