micrf102 Micrel Semiconductor, micrf102 Datasheet - Page 8

• Manufacturer Part Number: micrf102
• Description: Qwikradio? Uhf Ask Transmitter
• Manufacturer: Micrel Semiconductor

resonant at 5pF, the nominal mid-range value of the MICRF102
output stage varactor.
Using the equation:
If the inductance of the antenna cannot be set at the nominal
value determined by the above equation, a capacitor can
be added in parallel or series with the antenna. In this case,
the varactor internal to the MICRF102 acts to trim the total
capacitance value.
Supply Bypassing
Correct supply bypassing is essential. A 4.7µF capacitor in
parallel with a 100pF capacitor is recommended.
The MICRF102 is susceptible to supply-line ripple, if supply
regulation is poor or bypassing is inadequate, spurs will be
evident in the transmit spectrum.
MICRF102
L
=
4
π π
2 2
1
f C
+5V
RP1
(100k)
RP2
(6.8k)
C
VARACTOR
Crystal
Figure 5.
C
Figure 6. Application Test Circuit For Specifi cation Verifi cation
P
PC
VDD
VSS
REFOSC
C
S
MICRF102
L
ANTENNA
ANTM
ANTP
STBY
ASK
ASK DATA INPUT
L
ON
OFF
8
Transmit Power
The transmit power specifi ed in this datasheet is normalized
to a load of 50Ohm. The antenna effi ciency will determine
the actual radiated power. Good antenna design will yield
transmit power in the range of 67dBµV/m to 80dBµV/m at
3 meters.
The PC pin on the MICRF102 is used to set the transmit
power. The differential voltage on the output of the PA (power
amplifi er) is proportional to the voltage at the PC pin.
With more than 0.35V on the PC pin the output amplifi er
becomes current limited. At this point, further increase in
the PC pin voltage will not increase the RF output power in
the antenna pins. Low power consumption is achieved by
decreasing the voltage in the PC pin, also reducing the RF
output power and maximum range.
Output Blanking
When the device is fi rst powered up, or after a momentary
loss of power, the output is automatically blanked (disabled).
This feature ensures RF transmission only occurs under con-
trolled conditions when the synthesizer is fully operational,
plus preventing unintentional transmission at an undesired
frequency. Output blanking is key to guaranteeing compliance
with UHF regulations by ensuring transmission only occurs
in the intended frequency band.
Transformer Output to 50½
Impedance Transformation
Z1
Network
Z2
Z3
Spectrum Analyzer
Termination of
To 50½
December 2006