RFM110W Datasheet, PDF (13/22 Pages) List of Unclassifed Manufacturers – Low-Cost Consumer Electronics Applications

RFM110W/RFM117W
5.4 Power Amplifier
A highly efficient single-ended Power Amplifier (PA) is integrated in the RFM110W/RFM117W to transmit the modulated
signal out. Depending on the application, the user can design a matching network for the PA to exhibit optimum efficiency at
the desired output power for a wide range of antennas, such as loop or monopole antenna. Typical application schematics
and the required BOM are shown in “Chapter 4 Typical Application Schematic”. For the schematic, layout guideline and the
other detailed information please refer to “AN101 CMT211xA Schematic and PCB Layout Design Guideline”.
The output power of the PA can be configured by the user within the range from -10 dBm to +13 dBm in 1 dB step size using
the CMOSTEK USB Programmer and RFPDK.
5.5 PA Ramping
When the PA is switched on or off quickly, its changing input impedance momentarily disturbs the VCO output frequency. This
process is called VCO pulling, and it manifests as spectral splatter or spurs in the output spectrum around the desired carrier
frequency. By gradually ramping the PA on and off, PA transient spurs are minimized. The RFM110W/RFM117W has built-in
PA ramping configurability with options of 0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 and 1024 us, as shown in Figure 13. When
the option is set to “0”, the PA output power will ramp up to its configured value in the shortest possible time. The ramp down
time is identical to the ramp up time in the same configuration.
CMOSTEK recommends that the maximum symbol rate should be no higher than 1/2 of the PA ramping “rate”, as shown in the
formula below:
SR_Max ≤ 0.5 * (
1)
tRAMP
In which the PA ramping “rate” is given by (1/t_RAMP). In other words, by knowing the maximum symbol rate in the application,
the PA ramping time can be calculated by:
1
t_RAMP ≤ 0.5 * (
)
SRMAX
The user can select one of the values of the t_RAMP in the available options that meet the above requirement. If somehow the
t_RAMP is set to be longer than “0.5 * (1/SR_Max)”, it will possibly bring additional challenges to the OOK demodulation of the Rx
device. For more detail of calculating t_RAMP, please refer to “AN102 RFM110W/RFM117W Configuration Guideline”.
Logic 1
0 us
1 us
2 us
4 us
8 us
512 us
1024 us
Logic 0
Figure 13. PA Ramping Time
Time
Time
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