ata5773 ATMEL Corporation, ata5773 Datasheet - Page 31

• Manufacturer Part Number: ata5773
• Description: Microcontroller With Uhf Ask/fsk Transmitter
• Manufacturer: ATMEL Corporation

4.3
4.3.1
4.3.2
4510I–RKE–02/07
CLK Output
Clock Pulse Take-over
Output Matching and Power Setting
Figure 4-1.
Using C
tances on each side of the crystal of C
crystal of C
typical with worst case tolerances of ±16.25 kHz to ±28.01 kHz results.
An output CLK signal is provided for a connected microcontroller, the delivered signal is CMOS
compatible if the load capacitance is lower than 10 pF.
The clock of the crystal oscillator can be used for clocking the microcontroller. Atmel
ATARx9x has the special feature of starting with an integrated RC-oscillator to switch on the
T5753 with ENABLE = H, and after 1 ms to assume the clock signal of the transmission IC, so
that the message can be sent with crystal accuracy.
The output power is set by the load impedance of the antenna. The maximum output power is
achieved with a load impedance of Z
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 if the 1.0 pF output capacitance of the power amplifier is
compensated by the load impedance.
An optimum load impedance of:
Z
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 where the parallel imag-
inary part should be kept constant.
Output power measurement can be done with the circuit of
values must be changed to compensate the individual board parasitics until the T5753 has the
right load impedance Z
the output power must be calibrated out.
Load
S
= 400 || j/(2
to deliver the DC current.
4
= 8.2 pF ±5%, C
0
= 3.2 pF ±10% and a crystal with C
Tolerances of Frequency Modulation
XTAL
V
S
1.0 pF) = (255 + j192) thus results for the maximum output power of
Load,opt
5
= 10 pF ±5%, a switch port with C
C
= (255 + j192) . Also the damping of the cable used to measure
Stray1
Crystal equivalent circuit
Load,opt
C
Stray1
M
= (255 + j192) . There must be a low resistive path
L
= C
C
M
0
Stray2
M
= 13 fF ±10%, an FSK deviation of ±21.5 kHz
R
S
= 1 pF ±10%, a parallel capacitance of the
Figure
C
Switch
Stray2
C
5
4-2. Note that the component
= 3 pF ±10%, stray capaci-
C
Switch
C
4
T5753
®
’s
5