7

Equivalent Circuit Model

HSMP-389x Chip*

Typical Applications for HSMP-489x Low Inductance Series

Microstrip Series Connection for HSMP-489x Series

In order to take full advantage of the low inductance

of the HSMP-489x series when using them in series ap-

plications, both lead 1 and lead 2 should be connected

together, as shown in Figure 17.

A SPICE model is not available for PIN diodes as SPICE

does not provide for a key PIN diode characteristic, car-

rier lifetime.

0.3 nH

0.3 nH

0.3 pF

1.5 nH

1.5 nH

0.12 pF*

* Measured at -20 V

0.5

I = Forward Bias Current in mA

* See AN1124 for package models

20

0.3 pF

0.75 nH

Figure 16. Internal Connections.

Figure 17. Circuit Layout.

Figure 18. Circuit Layout.

Figure 19. Equivalent Circuit.

Microstrip Shunt Connections for HSMP-489x Series

In Figure 18, the center conductor of the microstrip

line is interrupted and leads 1 and 2 of the HSMP-489x

diode are placed across the resulting gap. This forces

the 1.5 nH lead inductance of leads 1 and 2 to appear as

part of a low pass filter, reducing the shunt parasitic in-

ductance and increasing the maximum available atten-

uation. The 0.3 nH of shunt inductance external to the

diode is created by the via holes, and is a good estimate

for 0.032" thick material.

Co-Planar Waveguide Shunt Connection for HSMP-489x Series

Co-Planar waveguide, with ground on the top side of

the printed circuit board, is shown in Figure 20. Since

it eliminates the need for via holes to ground, it offers

lower shunt parasitic inductance and higher maximum

attenuation when compared to a microstrip circuit.

Figure 20. Circuit Layout.

Figure 21. Equivalent Circuit.

1

2

3

HSMP-489x

50 OHM MICROSTRIP LINES

PAD CONNECTED TO GROUND

BY TWO VIA HOLES

Co-Planar Waveguide

Groundplane

Center Conductor

Groundplane