RF42/43
5.2. Power Amplifier
The RF42 contains an internal integrated power amplifier (PA) capable of transmitting at output levels between +11 to
+20 dBm. The output power is programmable in 3 dB steps through the txpow[2:0] field in "Register 6Dh. TX Power".
The RF43 contains a PA which is capable of transmitting output levels between –8 to +13 dBm.
The PA design is single-ended and is implemented as a two stage class CE amplifier with efficiency in the range of
45–50% while transmitting at maximum power. The efficiency drops to approximately 20% when operating at the
lowest power steps. Due to the high efficiency a simple filter is required on the board to filter the harmonics. The PA
output is ramped up and down to prevent unwanted spectral splatter.
5.2.1. Output Power Selection
With the RF42, the output power is configurable in 3 dB steps from +11 to +20 dBm with the txpow[2:0] field in
"Register 6Dh. TX Power". The PA output is ramped up and down to prevent unwanted spectral splatter.
Extra output power can allow use of a cheaper, smaller antenna reducing the overall BOM cost. The higher power
setting of the chip achieves maximum possible range, but of course comes at the cost of higher TX current
consumption. However, depending on the duty cycle of the system, the effect on battery life may be insignificant.
Contact HopeRF Support for help in evaluating this tradeoff.
The +13 dBm output power of the RF43 is targeted at systems that require lower output power. The PA still offers high
efficency and a range of output power from –8 to +13 dBm.
D7
D6
D5
D4
D3
D2
D1
D0
POR Def.
Add R/W Function/Description
R/W
TX Power
txpow[2] txpow[1]
txpow[0]
07h
6D
txpow[1:0]
RF42 Output Power
00
+11 dBm
01
10
11
+14 dBm
+17 dBm
+20 dBm
txpow[2:0]
RF43 Output Power
000
–8 dBm
001
010
011
100
101
110
111
–5 dBm
–2 dBm
+1 dBm
+4 dBm
+7 dBm
+10 dBm
+13 dBm
29
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E-mail: sales@hoperf.com
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