TDA5250D2_07 Datasheet, PDF (42/94 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

TDA5250 D2
Version 1.7
Application
tolerances of components affect matching too much. This will cause problems in a tuning-free mass
production of the application. A good CAE-tool will help to see the effects of component tolerances
on the input matching more accurate by tweaking each value.
A very high selectivity can be reached by using SAW-filters at the expense of higher cost and lower
sensitivity which will be reduced by the losses of the SAW-Filter of approx. 4dB.
Image-suppression:
Due to the quite high 1^st-IF of the frontend, the image frequency is quite far away. The image
frequency of the receiver is at:
f = f + 2 ∗ f = 868.3MHz + 2 * 289.4 = 1447.2MHz
IMAGE
SIGNAL
IF
[3 – 5]
The image suppression on the evalboard is about 16dB.
LO-leakage:
The LO of the 1^st Mixer is at:
f =f
* ⁴ = 868.3MHz ∗ ⁴ = 1157.73MHz
LO
3 ^RECEIVE
3
[3 – 6]
The LO-leakage of the evalboard on the RF-input is about –98dBm. This is far below the ETSI-
radio-regulation-limit for LO-leakage.
3.1.3 Switch in TX-Mode
The evalboard can be set into the TX-Mode by grounding the RX/TX-jumper on the evalboard or
programming the TDA5250 to operate in the TX-Mode. If the IC is programmed to operate in the
TX-Mode, the RX/TX-pin will act as an open drain output at a logical LOW. Then a DC-current can
flow from VCC to GND via L1, L2, D1, R1 and D2.
I _{PIN −DIODE}
= ^{Vcc − 2 ∗VFORWARD,PIN −DIODE}
R
1
[3 – 7]
Now both pin-diodes are biased with a current of approx. 0.3mA@3V and have a very low
impedance for RF.
Data Sheet
42
2007-02-26