RFPIC12C509AG Datasheet, PDF (41/104 Pages) Microchip Technology – 18/20-Pin 8-Bit CMOS Microcontroller with UHF ASK/FSK Transmitter

rfPIC12C509AG/509AF
7.6 Power Amplifier
The PLL output feeds the power amplifier (PA). The
open-collector differential output (ANT1, ANT2) can be
used to drive a loop antenna directly or converted to
single-ended output via an impenance matching net-
work or balanced-to-unbalanced (balun) transformer.
Pins ANT1 and ANT2 are open-collector outputs and
must be pulled-up to VDDRF through the load.
The differential output of the PA should be matched to
an impedance of 1 kΩ. Failure to match the impedance
will cause excessive spurious and harmonic emissions.
The transmit output power can be adjusted in six dis-
crete steps from +2 dBm to -12 dBm by varying the volt-
age (VPS) at the PS/DATAASK pin. Figure 7-6 shows an
example voltage divider network for ASK operation and
Figure 7-7 for FSK operation.
For FSK operation, the PS/DATAASK pin only serves as
a Power Select (PS) pin. An internal 20 µA current
source pushes current through the PS/DATAASK pin
resulting in a voltage drop across resistor R2 at the VPS
level selected for transmitter output power. VPS selects
the PA bias current. Higher transmit power will draw
higher current.
For ASK operation, the function of the PS/DATAASK pin
is to turn the Power Amplifier (PA) on and off. Resistors
R1 and R2 form a voltage divider network to apply volt-
age VPS for the selected transmitter output power. If
maximum transmitter output is desired, the output of a
GP0 pin can be connected directly to PS/DATAASK.
Table 7-5 lists typical values for R1 and R2 for both the
ASK and FSK modes.
FIGURE 7-6:
DATA IN
EXAMPLE ASK POWER
SELECT CIRCUIT
rfPIC12C509AG
VPS
R1
20µA
PS/DATAASK
To power
select
circuitry
R2
FIGURE 7-7: EXAMPLE FSK POWER
SELECT CIRCUIT
VPS
PS/DATAASK
rfPIC12C509AF
20µA
To power
select
circuitry
R2
TABLE 7-5: POWER SELECT ⁽¹⁾
Transmitter
Output Power
(dBm)
Transmitter
Operating Current
(mA)
Power Select (PS)
Voltage VPS
(Volts) ⁽²⁾
ASK
R1 (Ω)
R2 (Ω) ⁽³⁾
FSK
R2 (Ω)
+2
11.5
≥2.0
2400
4700
≥75K
-1
8.6
1.2
6800
4700
56K
-4
7.3
0.9
11K
4700
47K
-7
6.2
0.7
15K
4700
39K
-10
5.3
0.5
24K
4700
27K
-12
4.8
0.3
43K
4700
15K
-60
<4.8
<0.1
OPEN
4700
4700
Note 1: Standard Operating Conditions (unless otherwise stated) TA = 25°C, RFEN = 1,
VDDRF = 3V, fTRANSMIT = 433.92 MHz
2: VPS is actual voltage on PS/DATAASK pin.
3: The Power Select circuitry contains an internal 20 µA current source. To ensure that the transmitter output
power is at the minimum when transmitting a DATAASK = 0 (VSSRF), select the value of resistor R2 such
that the voltage drop across it is less than 0.1 volts.
© 2001 Microchip Technology Inc.
Preliminary
DS70031A-page 39