RFM67W Datasheet, PDF (14/37 Pages) List of Unclassifed Manufacturers – ISM TRANSMITTER MODULE

RFM 67W
5.3. The Power Amplifier
A simplified schematic of the dual power amplifiers of the RFM67W is shown in Figure 5. PA 1 comprises a pair of amplifiers:
One dedicated for low power use, LPA, for programmed powers from -18 to -3 dBm: The second for high power use, HPA,
for programmed powers from -2 to 13 dBm. PA 2 is a single high power amplifier and may be used in conjunction with PA 1
to deliver the full 17 dBm of output power.
pa_ramp_rising_time(6:5)
OOK
I/P
Ramp and
Control
LPA
HPA1
PA 1
VR_PA
RFOUT
Match
HPA2
PA 2
Figure 5. Simplified Schematic of the RFM67W Power Amplifier
The mode of operation of the PA’s is determined by the register setting pa_select(1:0) which is configured as shown in
Table 8, below. The output power of the PA is determined by the value of the register pow_val(4:0), with a single PA
enabled the output power is set by:
Pout = –18 dBm + pow_val(4:0)
The default setting for this register is 13 dBm. The expressions for the output power with other combinations of power
amplifier enabled are shown in Table 8. Note also that the power amplifier current limiter, over current protection (OCP),
feature of RFM67W can also limit the output power. To ensure correct operation at 17 dBm ensure that trim_ocp(3:0) is
set to 105 mA (‘1100’).
Table 8 Power Amplifier Mode Selection Truth Table
pa_select(1:0)
Mode
00
invalid
01
PA1 enabled
10
PA2 enabled
11
Dual PA
Power Range
-
-18 to 13 dBm
-
-13 to 17 dBm
Pout Formula
-18 dBm + pow_val(4:0)
-
-13 dBm + pow_val(4:0)
The ramp and power control features of the PA, determine the regulator output voltage which is used to power the
amplifiers, this must be done through an external RF choke.
Page 14
Tel: [phone] Fax: [phone] E-mail: [e-mail] http:/ / www.hoperf.com