Specifications

8.1.1 Radio External Components

In order to realise the full performance of the radio it is essential that the reference PCB layout and BOM are carefully

followed. See Appendix B.4.

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 JN5148 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

For single ended antennas or connectors, a balun is not required, however a matching network is needed.

The RF matching network requires three external components and the IBIAS pin requires one external component as

shown in schematic in B.4.1. These components are critical and should be placed close to the JN5148 pins and

analogue ground as defined in Table 8: JN5148 Printed Antenna Reference Module Components and PCB Layout

Constraints. Specifically, the output of the network comprising L2, C1 and L1 is designed to present an accurate

match to a 50 ohm resistive network as well as provide a DC path to the final output stage or antenna. Users wishing

to match to other active devices such as amplifiers should design their networks to match to 50 ohms at the output of

R1 43K

IBIAS

C20 100nF

L2 2.7nH

VB_RF

VREF

VB_RF2

RF_IN

C3 100nF

C12 47pF

VB_RF1

C1 47pF

L1 5.6nH

To Coaxial Socket

or Integrated Antenna

VB_RF

Figure 15 External Radio Components

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 JN5148 provides an output (ADO) on DIO12 that is asserted on odd numbered retries and optionally its

complement (ADE) on DIO13, that can be used to control an antenna switch; this enables antenna diversity to be

implemented easily (see Figure 16 and Figure 17).