PS13201

Data Sheet 210892 issue 3

Plessey Semiconductors Ltd.

Design & Technology Centre, Delta 500, Delta Business Park, Great Western Way, Swindon, UK SN5 7XE

Tel: +44 1793 518000

Fax: +44 1793 518030

7

a)

The device should be mounted on a ground plane, ensuring that the impedance between the ground plane

and ALL the GND pins is kept as low as possible. If a multilayer PCB is used where the ground plane is connected to

the GND pins using through-plated holes (vias), it is essential to ensure that the vias have a very low impedance. ALL

supply decoupling capacitors should be RF chip capacitors whose leads should be kept as short as possible.

b)

two layer PCB should help to achieve this.

c)

The RF input (pins 27 and 28) should be driven with a balanced source impedance. One way of achieving this is

to use an isolating BALUN transformer (50

UNBALANCED

50

BALANCED) connected between the signal

differential source impedance at pins 27 and 28. Use of a transmission line BALUN though, is NOT recommended.

d)

The RF Output connections (pins 9 and 10) should each be loaded with matched impedances ideally

50

transmission lines. The RF Output lines leading away from the device should be balanced. Driving highly

reactive SWR loads is NOT recommended as these can encourage device instability, as can an imbalance of the

differential load impedance at pins 9 and 10.

e)

The RF Output connections (pins 9 and 10) are DC coupled, and ideally the output pins should be capacitively

coupled to their loads using 1nF capacitors. However the RF Outputs can drive a DC load to GND and a DC offset of

approx. 400mV will exist on each RF Output pin. IT WILL NOT BE POSSIBLE TO DISABLE THE RF OUTPUT

BUFFER UNDER THESE CONDITIONS.

f)

The RF output (pins 9 and 10) has a tendency to limit on self noise, particularly at low ambient temperatures (-

55°C), when the RF output buffer is enabled.

NOTE that this will effect the limiting range as the gain of the RF output buffer will reduce as the amount of noise

limiting increases.

If required the limited RF Output can be attenuated using an attenuation network as shown in fig. 9. Under these

conditions the effective RF Output currents will be reduced, allowing the device to operate with a greater margin of

stability. It may be possible to run the device without a BALUN transformer on the RF input if the total output impedance

on the RF Output >> 50

, and the attenuation components are mounted as close as possible to the RF Output

connections (pins 9 and 10). The RF input connection could then be configured as in Fig 5.