High IIP2 at Baseband
Design Philosophies Enabling High IIP2 at Baseband
The pre-filtering of out-of-channel signals using a passive RC pole at the mixer output significantly improves the out-of-channel IIP2 of the baseband measured before the pole. Therefore, the pole is typically used at the mixer output. The effect of the pole on the out-ofchannel linearity is calculated later in application case IV. A high IIP2 with nonlinear circuit structures requires good matching, which in turn requires devices with large W and L in MOSFETs. This leads to higher parasitic capacitances, which decreases the speed of the circuit. A different design philosophy is to use small devices with large bandwidth and to use wideband feedbacks to linearize the circuits or key devices. The higher linearity allows larger mismatches to achieve the same IIP2 performance as the first method. However, the linearizing feedbacks have to be wide-band to effectively linearize the circuit with respect to out-ofchannel interfering signals.