DATA SHEET • SMP1302-085LF SURFACE MOUNT PIN DIODE

Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com

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June 5, 2012 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 200966L

Figure 5. Cross-Sectional View of the SMP1302-085LF

Figure 6. SMP1302-085LF Electrically Equivalent Circuit

The effects of these parasitic series inductances are negligible,

since they add a very small insertion loss to the shunt PIN but

have no effect on the isolation that the diode produces when it is

forward biased.

A cross section of the suggested printed circuit board design is

shown in Figure 7. The via shown in this view is critical, both for

electrical performance and for thermal performance. It is

recommended that several vias should be placed under the entire

footprint of the exposed paddle (pin 2) to minimize both electrical

inductance to the system ground and thermal resistance to the

system heat sink.

A Transmit/Receive Switch Design

A T/R switch incorporating a pair of SMP1302-085LF PIN diodes

and covering 2.0155 GHz to 2.0195 GHz has been designed and

tested. This circuit is shown in Figure 8. The switch operated

safely at a transmitter input power of +41 dBm CW (12.6 W) with

low insertion loss (0.42 dB) and high receiver isolation (37 dB).

The input 1 dB compression point is higher than +50 dBm. In the

receive state, the switch produced 0.45 dB insertion loss and

37.8 dB transmitter isolation.

The circuit is based on a quarter wave design using two shunt-

connected SMP1302-085LF diodes. In the transmit state, Bias 1 is

set at 0 mA and Bias 2 is set at 50 mA. Under these conditions,

D1 is held out of conduction so its impedance remains high and a

very small insertion loss is introduced to the path between the

transmitter port and the antenna port.

D2 is forced into conduction, which lowers its series resistance

towards its minimum value of <1

Ω. In this state, energy that

propagates from either the transmitter port or the antenna port is

reflected, which isolates the receiver port from the remainder of

the circuit.