Design with PIN Diodes

Rev. V3

AG312

3

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Switching Speed Model

The switching speed in any application depends on the

driver circuit as well as the PIN diode. The primary PIN

properties that influence switching speed may be ex-

plained as follows:

A PIN diode has two switching speeds from forward bias

to reverse bias TFR, and from reverse bias to forward

bias TRF. The diode characteristic that affects TFR is τ,

carrier lifetime. The value of TFR may be computed from

the forward current IF, and the initial reverse current IR,

as follows:

Figure 3

TRF depends primarily on I-region width, W, as indicated

in the following chart which shows typical data:

I-Width To 10 mA from To 50 mA from

µm

10 V

100 V

10 V

100 V

10 V

100 V

175

7.0 µS

5.0 µS

3.0 µS

2.5 µS

2.0 µS

1.5 µS

100

2.5 µS

2.0 µS

1.0 µS

0.8 µS

0.6 µS

0.6 µS

50

0.5 µS

0.4 µS

0.3 µS

0.2 µS

0.2 µS

0.1 µS

To 100 mA from

Thermal Model

mined by the following equation:

(usually 175°C) and TA is the ambient or heat sink tem-

perature. Power dissipation may be computed as the

product ot the RF current squared multiplied by the diode

For CW applications the value of thermal resistance, θ,

In most pulsed RF and microwave applications where the

duty factor, DF, is less than 10 percent and the pulse

diode, good approximation of the effective value of θ in

the above equation may be computed as follows:

The

following

diagram

indicates

how

junction

temperature is affected during a pulsed RF application.

PIN Diode Applications

Figure 4