T5753 ATMEL Corporation, T5753 Datasheet - Page 5

• Manufacturer Part Number: T5753
• Description: UHF ASK/FSK TRANSMITTER
• Manufacturer: ATMEL Corporation

Output Matching and Power
Setting
Application Circuit
4510F–RKE–07/04
The output power is set by the load impedance of the antenna. The maximum output
power is achieved with a load impedance of Z
low resistive path to V
The delivered current pulse of the power amplifier is 9 mA and the maximum output
power is delivered to a resistive load of 400
power amplifier is compensated by the load impedance.
An optimum load impedance of:
Z
power of 8 dBm.
The load impedance is defined as the impedance seen from the T5753’s ANT1, ANT2
into the matching network. Do not confuse this large signal load impedance with a small
signal input impedance delivered as input characteristic of RF amplifiers and measured
from the application into the IC instead of from the IC into the application for a power
amplifier.
Less output power is achieved by lowering the real parallel part of 400
parallel imaginary part should be kept constant.
Output power measurement can be done with the circuit of Figure 5. Note that the com-
ponent values must be changed to compensate the individual board parasitics until the
T5753 has the right load impedance Z
cable used to measure the output power must be calibrated out.
Figure 5. Output Power Measurement
For the blocking of the supply voltage a capacitor value of C
mended (see Figure 6 on page 6 and Figure 7 on page 7). C
the loop antenna to the power amplifier where C
10.8 pF/NP0 (18 pF + 27 pF in series); for C
achieve a better tolerance value and to have the possibility to realize the Z
using standard valued capacitors.
C
loop that suppresses the 1
Normally the best suppression is achieved when C
pins ANT1 and ANT2.
The loop antenna should not exceed a width of 1.5 mm, otherwise the Q-factor of the
loop antenna is too high.
L
on the load resonance frequency of the crystal. Normally, a value of 12 pF results for a
15 pF load-capacitance crystal.
1
Load
1
([50 nH to 100 nH) can be printed on PCB. C
forms together with the pins of T5753 and the PCB board wires a series resonance
= 400
|| j/(2
ANT1
ANT2
S
to deliver the DC current.
1.0 pF) = (255 + j192)
~
st
Z
harmonic, hence the position of C
Lopt
C
C
L
V
2
1
1
S
= 3.3p
= 56n
= 1n
Load,opt
2
= (255 + j192) . Also the damping of the
two capacitors in series should be used to
Load,opt
Z = 50
if the 1.0 pF output capacitance of the
4
thus results for the maximum output
should be selected that the XTO runs
1
is placed as close as possible to the
1
= (255 + j192) . There must be a
typically is 22 pF/NP0 and C
1
Power
meter
1
and C
3
on the PCB is important.
50
= 68 nF/X7R is recom-
R
in
2
are used to match
T5753
where the
Load,opt
2
by
is
5