PIN diode Vector Modulators -

Fundamentals and Drive Requirements

Rev. V4

Application Note

AN3001

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PCB Design Guidelines

The outline drawing for the vector modulator is provided in Figure 7. The recommended PC board layout is pro-

vided in Figure 8. Note that the topology of the bias components on the layout is similar to the topology of bias

components on the schematic. It is important to have the inductors as close to the vector modulator as possible.

If the inductors are rotated around the Smith chart, they will look like capacitors, and will not provide the high

impedance to the RF signal. If the RF signal is not blocked, there can be coupling between the output ports of

the 90

° hybrids, which will degrade the performance of the vector modulator. The capacitors should be centered

between the inductors and as close as possible to the inductors, as shown in the PC board layout.

The paddle (base) of the package is grounded to optimize the RF performance of the vector modulator. A chip

scale package (CSP) was used to minimize the amount of PC board space that the end user would require.

There are two RF connections (RF IN and RF OUT) and four bias connections. All of the other connections are

ground. RF IN and RF OUT should be connected to 50 ohm transmission lines. It is preferred to select the PC

board material so that the RF lines are less than 20 mils wide to minimize coupling from the RF lines to the bias

circuit. The lines in the bias circuit should be approximately 6 mils wide to minimize cross coupling.

The recommended solder for mounting surface mount packages is Sn63 (63% Sn, 37% Pb) because it is a

eutectic compound with a melting point (183ºC) high enough to exceed the standard operating limit of the de-

vices, but low enough to avoid damaging internal circuitry during proper solder reflow operations.

Figure 3. Schematic of Dual Linearizer Driving Vector Modulator