ABSTRACT
Nowadays, on-chip transformers are widely used to implement functions such as impedance conversion, resonant loads, low-noise feedback in amplifiers, bandwidth enhancement, and differential-to-single conversion (Zhou and Allstot 1998; Cassan and Long 1999; Long 2000; Bhatti, Roufoogaran, and Castaneda 2005; Kwok and Luong 2005). Because the amount of silicon area occupied by transformers can be a limiting factor in most applications, interleaved or tapped structures are often replaced by stacked configurations, which offer higher magnetic coupling and area efficiency, although at the expense of increased parasitic capacitances. Patterned ground shields can be profitably exploited in all transformer configurations to reduce losses caused by eddy currents flowing into the substrate (Niknejad and Meyer 2001; Ng, Rejaei, and Burghartz 2002).
