Figure 1-11: ESP8266EX crystal oscillators
RF Design
The characteristic impedance that RF lines control is 50 Ω, in order to ensure the complete
board on the second layer. The surrounding drilled hole should be blocked and the lines should
be as short as possible. The width of RF lines should be not less than 6 mil, and above 10 mil is
better.
A π matching circuit near the RF Pin should be reserved in RF lines. RF lines connecting the
chip and antenna should not cover drills, which means cross layer lines are not allowed.
RF lines should not be set at a vertical, or a 45-degree angle. Circular lines are allowed if
necessary. No signal lines of high frequency should be set near RF lines.
RF antenna should be set away from high frequency transmitting devices, such as crystal
oscillators, DDR, and certain high frequency clocks (SDIO_CLK, etc).
Figure 1-12: ESP8266EX RF
1.5.2.
ESP8266EX as Slave Device
When ESP8266EX works with other master CPU as a slave device, signal integrity in layout
design is more important than the standalone mode. It is important to keep ESP8266EX away
from the interferences caused by complicity of the system and high frequency signals.
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