User Manual

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24 JN-DS-JN5139 v1.5 © Jennic 2008
8.1.1 Radio External components
The VCO loop filter requires three external components and the IBIAS pin requires one external component as shown
in Figure 15. These components should be placed close to the JN5139 pins and analogue ground.
15
VCOTUNE
3n3F
330pF
4k7
1%
VB_VCO
19
43k
1%
VSSA
IBIAS
VSSA
100nF
Figure 15: VCO Loop Filter and IBIAS
The radio is powered from a number of internal 1.8V regulators fed from the analogue supply VDD1, in order to
provide good noise isolation between the digital logic of the JN5139 and the analogue blocks. These regulators are
also controlled by the baseband controller and protocol software to minimise power consumption. Decoupling for
internal regulators is required as described in section 2.2.1, Power Supplies.
8.1.2 Antenna Diversity
Support is provided for antenna diversity. Antenna diversity is a technique that maximises the performance of an
antenna system. It allows the radio to switch between two antennas that have very low correlation between their
received signals. Typically, this is achieved by spacing two antennas around 0.25 wavelengths apart or by using two
orthogonal polarisations. So, if a packet is transmitted and no acknowledgement is received, the radio system can
switch to the other antenna for the retry, with a different probability of success.
The JN513x provides an output on DIO12 that is asserted on odd numbered retries that can be used to control an
antenna switch; this enables antenna diversity to be implemented easily (see Figure 16 and Figure 17)
Antenna A
ADO (DIO[12])
Antenna B
Device RF Port
RF Switch: Single-Pole, Double-Throw (SPDT)
A B
COM
SEL
SELB
Figure 16 Simple Antenna Diversity Implementation using External RF Switch