RFM110W Datasheet, PDF (14/22 Pages) List of Unclassifed Manufacturers – Low-Cost Consumer Electronics Applications

RFM110W/RFM117W
5.6 Crystal Oscillator and RCLK
The RFM110W/RFM117W uses a 1-pin crystal oscillator circuit with the required crystal load capacitance integrated on-chip.
Figure
14 shows the configuration of the XTAL circuitry and the crystal model. The recommended specification for the crystal is 26
MHz with ±20 ppm, ESR (Rm) < 60 Ω, load capacitance C_LOAD ranging from 12 to 20 pF. To save the external load capacitors, a
set of variable load capacitors C_L is built inside the RFM110W/RFM117W to support the oscillation of the crystal.
The value of load capacitors is configurable with the CMOSTEK USB Programmer and RFPDK. To achieve the best
performance, the user only needs to input the desired value of the XTAL load capacitance C_LOAD of the crystal (can be found in
the datasheet of the crystal) to the RFPDK, then finely tune the required XO load capacitance according to the actual XO
frequency. Please refer to “AN103 CMT211xA-221xA One-Way RF Link Development Kits Users Guide” for the method of
choosing the right value of C_L.
Crystal Model
Rm
RFM110W/11
7
XTAL
RCLK
26 MHz
RFM110W/RFM117W
Cc
XTAL
0. 3 – 0. 7 Vpp
Cm
C0
CL
CL
Lm
Figure 14. XTAL Circuitry and Crystal Model
Figure 15. RCLK Circuitry
If a 26 MHz RCLK (reference clock) is available in the system, the user can directly use it to drive the RFM110W/RFM117W by
feeding the clock into the chip via the XTAL pin. This further saves the system cost due to the removal of the crystal. A
coupling capacitor is required if the RCLK is used. The recommended amplitude of the RCLK is 0.3 to 0.7 Vpp on the XTAL
pin. Also, ^{the user should set the internal load capacitor C}L ^{to its minimum value. See Figure 15 for the RCLK circuitry.}
E‐mail:[e-mail] website://www.hoperf.com
Rev 1.0 | Page 14/21