Programming instructions

RF Components
Multisim Component Reference Guide 14-2 ni.com
14.2 RF Inductor
From many types of RF inductors, spiral inductors provide higher inductance values and
higher Qs. The spiral inductor is a technique of forming a planar inductor in a small place.
The shape is described by an increasing radius with angle: i.e. R = r/I + k
θ
The equivalent circuit is a combination of series resistor (due to skin effect) and inductor, and
shunt capacitors (due to the distance between the surface which embraces the conductor, and
the ground plane). The quality of the inductor, usually noted as Q, is higher for spiral
inductors than those of other types of inductors, such as the rectangular spiral.
14.3 RF Bipolar Transistors
Basic operation of an RF bipolar transistor is identical to that of transistors designed for low
frequencies. RF transistors, however, have a higher maximum operating frequency (W
t
),
depending on base and collector transit and charging times. To achieve this, the physical size
of emitter/base/collector areas at the layout level are minimized. However, reduction in the
base area is limited by the technology used to fabricate the transistor. Reduction in the
collector area is limited by the maximum tolerable voltage at the collector terminal. To
achieve maximum power output, the emitter periphery area should be as large as possible.
Because of these limitations, a special structure for bipolar transistors is used. This structure is
commonly referred to as an interdigital bipolar transistor.
ComponentRef.book Page 2 Thursday, December 7, 2006 10:12 AM