A monolithic transformer coupled 5-W silicon power amplifier with 59% PAE at 0.9 GHz

Surface-passivated high-resistivity silicon as a true microwave substrate

“…Planar transformers are currently of great interest to the monolithic-microwave integrated-circuit (MMIC) design community since they can provide interstate matching in single-ended, as well as differential configurations [20]. Furthermore, their applicability as a feedback element or balun allows for novel on-chip design techniques, resulting in higher circuit performance [21].…”

“…This, however, brings several technological issues in focus that may form bottlenecks, in particular the considerable losses in the conventional silicon substrates [6]. Currently, resistivities of at most [10][11][12][13][14][15][16][17][18][19][20] cm [low-resistivitysilicon(LRS)]arebeingused.Thiscorrespondsto conductivities that lead to considerable substrate losses and, thus, to excessive attenuation of integrated transmission lines [7] and reduced quality factors of on-chip inductors [8]. III-V-based processes have ideal substrates in that respect, but these lack other important properties such as high thermal conductivity and high and frequency-independent permittivity that qualify silicon as a true microwave substrate [7].…”

A 21-26-GHz SiGe bipolar power amplifier MMIC

“…The difficulties of single-ended amplifier design are avoided when a differential topology is used [38]- [41]. An example is shown in Fig.…”

“…A balun (balanced-to-unbalanced transformer) is needed to convert the differential signals from the final gain stage to a single-ended 50-output (i.e., antenna). Baluns can be implemented off-chip [38], but on-chip L-C baluns are a compact and integrated solution in the mm-wave frequency range [39]. Asymmetry in the balun response causes the transformed load impedance to appear inductive at one of the balanced output ports and capacitive at the other.…”

“…Here the transistors are driven differentially so that a virtual ground exists on-chip to minimize ground inductance. The matching network between the gain stages can be implemented using a monolithic transformer with a non-1:1 turns ratio [38], [39].…”