Data Sheet
3.4 Radio 3 FUNCTIONAL DESCRIPTION
In addition to this, ESP32 has an internal 8 MHz oscillator, of which the accuracy is guaranteed by design and
is stable over temperature (within 1% accuracy). Hence, the application can then select from the external crystal
clock source, the PLL clock or the internal 8 MHz oscillator. The selected clock source drives the CPU clock,
directly or after division, depending on the application.
3.3.2 RTC Clock
The RTC clock has five possible sources:
• external low speed (32 kHz) crystal clock
• external crystal clock divided by 4
• internal RC oscillator (typically about 150 kHz and adjustable)
• internal 8 MHz oscillator
• internal 31.25 kHz clock (derived from the internal 8 MHz oscillator divided by 256)
When the chip is in the normal power mode and needs faster CPU accessing, the application can choose the
external high speed crystal clock divided by 4 or the internal 8 MHz oscillator. When the chip operates in the low
power mode, the application chooses the external low speed (32 kHz) crystal clock, the internal RC clock or the
internal 31.25 kHz clock.
3.3.3 Audio PLL Clock
The audio clock is generated by the ultra low noise fractional-N PLL. The output frequency of the audio PLL is
programmable, from 16 MHz to 128 MHz, given by the following formula:
f
out
=
f
xtal
N
div
M
div
2
K
div
where f
out
is the output frequency, f
xtal
is the frequency of the crystal oscillator, and N
div
, M
div
and K
div
are all
integer values, configurable by registers.
3.4 Radio
The ESP32 radio consists of the following main blocks:
• 2.4 GHz receiver
• 2.4 GHz transmitter
• bias and regulators
• balun and transmit-receive switch
• clock generator
3.4.1 2.4 GHz Receiver
The 2.4 GHz receiver down-converts the 2.4 GHz RF signal to quadrature baseband signals and converts them
to the digital domain with 2 high-resolution, high-speed ADCs. To adapt to varying signal channel conditions,
RF filters, Automatic Gain Control (AGC), DC offset cancelation circuits and baseband filters are integrated within
ESP32.
Espressif Systems 14 http://www.espressif.com