ATA5749 ATMEL Corporation, ATA5749 Datasheet - Page 5

• Manufacturer Part Number: ATA5749
• Description: Fractional-n PLL Transmitter IC
• Manufacturer: ATMEL Corporation

9128C–RKE–10/08
The PA is enabled when the PLL is locked and the configuration register programming is com-
pleted. Upon enabling PA at FSK-mode, the RF output power will be switched on. At ASK mode,
the input signal must be additionally set high for RF at output pins. The output power is user pro-
grammable from –0.5 dBm to +12.5 dBm in steps of approximately 1 dB. Changing the output
power requirements, you also modify the current consumption. This gives the user the option to
optimize system performance (RF link budget versus battery life). The PA is implemented as a
Class-C amplifier, which uses an open-collector output to deliver a current pulse that is nearly
independent from supply voltage and temperature. The working principle is shown in
Figure 3-1.
The peak value of this current pulse I
±20%, which corresponds to about 1.5 dB variation in output power for a given power setting
under typical conditions. The actual value of I
PWR. This allows the user to scale both the output power and current consumption to optimal
levels.
ASK modulation is achieved by using the SDIN_TXDIN signal where a HIGH on this pin corre-
sponds to RF carrier “ON” and a LOW corresponds to RF “OFF”. FSK uses the same signal path
but HIGH switch on the upper FSK-frequency.
Power Meter
Class C Power Amplifier Output
50
I
Pulse
C2
= (PWR[0:3])
V
Z
S
L1
LOPT
V
V
ANT1
I
ANT1
ANT2
Pulse
V
S
is calibrated during ATA5749 production to about
ANT1
ANT2
Pulse
5
4
can be programmed with the 4-bit value in
ATA5749 [Preliminary]
I
ANT2
Figure
3-1.
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