TDA5250D2_07 Datasheet, PDF (19/94 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

2.4
Functional Block Description
TDA5250 D2
Version 1.7
Functional Description
2.4.1 Power Amplifier (PA)
The power amplifier is operating in C-mode. It can be used in either high or low power mode. In
high-power mode the transmit power is approximately +13dBm into 50 Ohm at 5V and +4dBm at
2.1V supply voltage. In low power mode the transmit power is approximately -7dBm at 5V and -
32dBm at 2.1V supply voltage using the same matching network. The transmit power is controlled
by the D0-bit of the CONFIG register (subaddress 00H) as shown in the following Table 2-2. The
default output power mode is high power mode.
Table 2-2
Bit
D0
Sub Address 00H: CONFIG
Function
Description
PA_PWR
0= low TX Power, 1= high TX Power
Default
1
In case of ASK modulation the power amplifier is turned fully on and off by the transmit baseband
data, i.e. 100% On-Off-Keying.
2.4.2 Low Noise Amplifier (LNA)
The LNA is an on-chip cascode amplifier with a voltage gain of 15 to 20dB and symmetrical inputs.
It is possible to reduce the gain to 0 dB via logic.
Table 2-3
Bit
D4
Sub Address 00H: CONFIG
Function
Description
LNA_GAIN
0= low Gain, 1= high Gain
Default
1
2.4.3 Downconverter 1^st Mixer
The Double Balanced 1^st Mixer converts the input frequency (RF) in the range of 868-870 MHz
down to the intermediate frequency (IF) at approximately 290MHz. The local oscillator frequency is
generated by the PLL synthesizer that is fully implemented on-chip as described in Section 2.4.5.
This local oscillator operates at approximately 1157MHz in receive mode providing the above
mentioned IF frequency of 290MHz. The mixer is followed by a low pass filter with a corner
frequency of approximately 350MHz in order to prevent RF and LO signals from appearing in the
290MHz IF signal.
2.4.4 Downconverter 2^nd I/Q Mixers
The Low pass filter is followed by 2 mixers (inphase I and quadrature Q) that convert the 289MHz
IF signal down to zero-IF. These two mixers are driven by a signal that is generated by dividing the
local oscillator signal by 4, thus equalling the IF frequency.
Data Sheet
19
2007-02-26