!
!
!
Espressif Systems
ESP8266EX
Hardware User Guide
When using the downloading tools, please remember to select the right crystal oscillator type. In
circuit design, capacitors C1 and C2, which are connected to the earth, are added to the input and
output terminals of the crystal oscillator respectively. The values of the two capacitors can be
flexible, ranging from 6pF to 22pF, however, the specific capacitive values of C1 and C2 depend on
further testing and adjustment on the overall performance of the whole circuit. Normally, the
capacitive values of C1 and C2 are within 10pF if the crystal oscillator frequency is 26MHz, while the
values of C1 and C2 are 10pF<C1, C2<22pF if the crystal oscillator frequency is 40MHz.
Figure 7 ESP8266EX Crystal oscillators
Note: Defects in the craftsmanship of the crystal oscillators (for example, high frequency deviation,
unstable working temperature) may lead to the malfunction of ESP8266EX, resulting in the decrease
of overall performance.
2.2.5.
RF
The output impedance of RF pin (Pin 2) is 50 ohm. Normally, when the antenna impedance
approaches 50 ohm, antenna matching is not necessary. However, low-price antenna commercially
available in the market does not feature 50 ohm impedance. Besides, the impedance in 2.4G to 2.5G
frequency band is rather scattered. Therefore, N-type matching network is essential in circuit design
to facilitate antenna matching.
Espressif Systems
/
Jun 1, 2015
16 48