MC68HC908RF2 Datasheet, PDF (224/254 Pages) Motorola, Inc – HCMOS Microcontroller Unit

PLL Tuned UHF Transmitter Module
16.5 RF Output Stage
The output stage is a single-ended square wave switched current
source. Harmonics will be present in the output current drive. Their
radiated absolute level depends on the antenna characteristics and
output power. Typical application demonstrates compliance to European
Telecommunications Standards Institute (ETSI) standard.
A resistor R_EXT connected to the REXT pin controls the output power
allowing a tradeoff between radiated power and current consumption.
The output voltage is internally clamped to V_CC ± 2 V_BE (typically
V_CC ±1.5 V @ T_A = 25°C).
16.6 Modulation
If a low-logic level is applied on pin MODE, then the on/off keying (OOK)
modulation is selected. This modulation is performed by switching on/off
the RF output stage. The logic level applied on pin DATA controls the
output stage state:
DATA = 0 → output stage off
DATA = 1 → output stage on
If a high-logic level is applied on pin MODE, then frequency shift keying
(FSK) modulation is selected. This modulation is achieved by
modulating the frequency of the reference oscillator. This frequency
change is performed by switching the external crystal load capacitor.
The logic level applied on pin DATA controls the internal switch
connected to pin CFSK:
DATA = 0 → switch off
DATA = 1 → switch on
In case of Figure 16-5, where the two capacitors C6 and C9 are in
series:
DATA = 0 leads to the high value of the carrier frequency
DATA = 1 leads to the low value of the carrier frequency
Advance Information
224
PLL Tuned UHF Transmitter Module
MC68HC908RF2 — Rev. 1
MOTOROLA