The first question that arises is why optimization is required at all. The primary reason is that there are imbalances in the Gilbert cell mixers and phase error introduced by the phase-shifting network. These imperfections are caused by slight differences in devices on the same die. There are also imbalances and offsets between the in-phase and quadrature signal paths as a result of process variations. These errors are not present in an ideal device, however they cannot be eliminated in practice. The second question then would be how to compensate the device to optimize the performance. To understand how compensation can be achieved, it is helpful to understand how sideband suppression, carrier suppression, amplitude error and phase error are related. The block diagram of a typical quadrature modulator is shown in Figure 1.