CMT2157AW
Rev 0.8 | Page 15/31
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Category
Parameters
Descriptions
Default
Mode
Periodic Time
This parameter is only available when Periodic
Transmission is turned on. It defines the periodic
time for transmitting a fixed set of data. The
range is from 2 to 7683.512 s, accurate to 3
decimal points. It is only available when Periodic
Transmission is on.
1.000 s
Advanced
Study Settings
ID Study
Turn on/off the Sync ID study function, the
options are: On or Off. The ID Study is only
supported in 1920 and 1527 mode.
Off
Advanced
Study Trigger
Time
This parameter is only available when ID Study is
turned on. It defines the time from the instance of
pressing the study button to the instance at which
the device starts to transmit the study packets.
The range is from 1 to 15 second(s).
5 s
Advanced
Study Button
This parameter is only available when ID Study is
turned on. It defines which button is used to
trigger the transmission of the study packets. The
options are the current buttons used in the Push
Button Settings.
Pin 11 (K1)
Advanced
Study Power
This parameter is only available when ID Study is
turned on. It defines the PA power when the
device is transmitting the study packets. The
range is from –10 to +14 dBm.
-6 dBm
Basic
Advanced
5.4 Power Amplifier
A highly efficient single-ended Power Amplifier (PA) is integrated in the CMT2157AW 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 “AN111 CMT215x 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
phenomenon 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 CMT2157AW 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
t
RAMP
)
