NXP Semiconductors MKW01Z128, Reference Manual

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Sub 1 GHz Transceiver Architecture Description
MKW01xxRM Reference Manual, Rev. 3, 04/2016
Freescale Semiconductor, Inc. 5-3
5.5 Frequency Synthesis
The LO generation on the MKW01Z128 transceiver is based on a state-of-the-art fractional-N PLL. The
PLL is fully integrated with automatic calibration.
5.5.1 Reference Oscillator
The crystal oscillator is the main timing reference of the MKW01Z128. It is used as a reference for the
transceiver frequency synthesizer and as a clock for the digital processing. In turn, the transceiver ClkOut
signal can be used to provide an external reference clock for the MCU (see
Section 4.4, “System Clock
Sources and Configurations” ).
The XO startup time, TS_OSC, depends on the actual XTAL being connected on pins XTA and XTB.
When using the built-in sequencer, the device optimizes the startup time and automatically triggers the
PLL when the XO signal is stable. To manually control the startup time, the user should either wait for
TS_OSC max, or monitor the signal CLKOUT which will only be made available on the output buffer
when a stable XO oscillation is achieved.
An external clock can be used to replace the crystal oscillator, for instance a tight tolerance TCXO. To do
so, Bit 4 at transceiver Address 0x59 should be set to 1, and the external clock has to be provided on XTA
(Pin 4). XTB (pin 5) should be left open. The peak-peak amplitude of the input signal must never exceed
1.8 V. Please consult your TCXO supplier for an appropriate value of decoupling capacitor, C
D
.
Figure 5-2. TCXO Connection
5.5.2 CLKOUT Output
The reference frequency, or a fraction of it, can be provided on DIO5 (pin 54) by modifying bits ClkOut
in RegDioMapping2 . Two typical applications of the CLKOUT output include:
• Provide a clock output for the MCU (see Section 4.4, “System Clock Sources and Configurations” )
- saves the cost of an additional crystal. CLKOUT can be made available in any operation mode
except Sleep mode and is automatically enabled at power-on reset.
• Provides an oscillator reference output - allows simple software trimming of the initial crystal
tolerance.
If the transceiver is put into low power mode, ClkOut may be disabled for lowest power.
XTA XTB
32 MHz
TCXO
NC
OP
Vcc
GND
C
D
Vcc