Abstract

Monolithic integrated circuit switches can be fabricated using either GaAs FETs or with PIN diodes as the active elements. Each offers advantages and disadvantages to the circuit design. It has been shown that because of their higher switching Q1,4 that PIN diodes should exhibit lower loss and higher isolation in the same circuit than a switch made with a FET as the switching element. Conversely, FET based switches offer an advantage of less control power and better DC to RF isolation of the control currents. This paper will discuss a family of MMIC PIN diode based SPDT switches which are designed to give the lowest loss and best isolation from 2-18 GHz. In order to minimize losses from the passive elements such as inductors, capacitors and RF lines, these are built in a GMIC3 circuit (glass microwave circuit). The active elements (PIN diodes) are built on a HETEROLITHIC circuit. In a HETEROLITHIC circuit the PIN switching elements are suspended in a low loss tangent, low dielectric borosilicate glass. This glass reduces the normal loss seen in RF lines on silicon or gallium arsenide. It's smaller dielectric also allows larger conductor lines, without excess capacitance to ground. The GMIC circuit is designed to allow either a silicon PIN or GaAs PIN switch interchangeable as the active element. Several broadband circuits were built with the designed frequency being 2-18 GHz. Electrical results are excellent, with loss (including all circuit elements) being -0.8 dB at 18 GHz and isolation being >35 dB.