RFHCS362G_11 Datasheet, PDF (31/54 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder with UHF ASK/FSK Transmitter

rfHCS362G/362F
6.6 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 800 to 1000 Ω. Failure to match the
impedance may cause excessive spurious and har-
monic emissions. For more information see Application
Note AN831, Matching Small Loop Antennas to rfPIC
Devices.
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 6-5 shows an
example voltage divider network for ASK operation and
Figure 6-6 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 6-6 lists typical values for R1 and R2 for both the
ASK and FSK modes.
.
Note: PS/DATAASK is driven low when RFENIN = 0.
Make sure external circuitry on PS/DATAASK
does not conflict by driving the pin high. The
encoder DATA output works because it is low if
RFENOUT is low
FIGURE 6-5:
DATA IN
EXAMPLE ASK POWER
SELECT CIRCUIT
rfHCS362G/362F
VPS
R1
20μA
PS/DATAASK
To power
select
circuitry
R2
FIGURE 6-6: EXAMPLE FSK POWER
SELECT CIRCUIT
rfHCS362G/362F
VPS
20μA
PS/DATAASK
To power
select
circuitry
R2
TABLE 6-6: POWER SELECT ⁽¹⁾
Transmitter
Output Power
(dBm)
+2
-1
-4
-7
-10
-12
-60
Transmitter
Operating Current
(mA)
11.5
8.6
7.3
6.2
5.3
4.8
<4.8
Power Select (PS)
Voltage VPS
(Volts) ⁽²⁾
≥2.0
1.2
0.9
0.7
0.5
0.3
<0.1
ASK
R1 (Ω)
R2 (Ω) ⁽³⁾
2400
6800
11K
15K
24K
43K
OPEN
4700
4700
4700
4700
4700
4700
4700
FSK
R2 (Ω)
≥75K
56K
47K
39K
27K
15K
4700
© 2011 Microchip Technology Inc.
DS41189B-page 31