Rf Circuit; Rf Power Pin; Rf Matching Circuit; Rf Trace Impedance - Realtek RTL8762C Hardware Instructions

RTL8762C Evaluation Board User Manual

12 RF Circuit

12.1 RF Power Pin

VD12_PA, VD12_SYN and VD12_TRX are the power input pins for RF transmitter and receiver.
VD12_PA, VD12_SYN and VD12_ TRX should be powered with 1.2V which can be obtained
from VDDCORE.
Decoupling capacitors should be added separately to these three pins, and placed right in front of
the power input pin.

12.2 RF Matching Circuit

In order to achieve efficient power transmission from RFIO to antenna, a matching circuit is
required. A return loss greater than 10 dB means that 90% of the power is transmitted to the
antenna.
22pF
(optional)
Matching for IC Matching for antenna
IC
L C L
C C C C
Zin Zin
1 2
In the figure above, 3 components are used for matching the IC RF trace and 3 components are
used for matching the antenna. The purpose is to obtain 50 ohm input impedance for both Zin,1
and Zin,2. The 100pF capacitor for DC blocking may be optional only if the chosen antenna is
PCB antenna or chip antenna.
The matching network in IC RF trace is also designed for harmonic suppression. It is strongly
recommended to follow Realtek HDK instruction, and choose exactly the same products as those
in QVL. Otherwise, the performance cannot be guaranteed.
The chosen value for antenna matching depends on the design. Sometimes, antenna matching can
be achieved by using only 2 components. However, the space for 3 components should be
reserved, because fine-tuning is performed at the later stage of the design.

12.3 RF trace impedance

The impedance of trace for RF signal should be designed at 50 ohm. The impedance depends on
the following factors and should be designed carefully:
20