TDA5252G2 INFINEON [Infineon Technologies AG], TDA5252G2 Datasheet - Page 40

• Manufacturer Part Number: TDA5252G2
• Description: ASK/FSK 915MHz Wireless Transceiver
• Manufacturer: INFINEON [Infineon Technologies AG]

The noise figure of the LNA-input-matching network is equal to its losses. The input matching
network is always a compromise of sensitivity and selectivity. The loaded Q should not get too high
because of 2 reasons:
more losses in the matching network and hence less sensitivity
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
frequency of the receiver is at:
The image suppression on the evalboard is about 17dB.
LO-leakage:
The LO of the 1
The LO-leakage of the evalboard on the RF-input is about –90dBm.
3.1.3
The evalboard can be set into the TX-Mode by grounding the RX/TX-jumper on the evalboard or
programming the TDA5255 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.
Now both pin-diodes are biased with a current of approx. 0.3mA@3V and have a very low
impedance for RF.
Data Sheet
I
f
PIN
LO
f
IMAGE
=
−
DIODE
f
RECEIVE
=
Switch in TX-Mode
=
f
SIGNAL
Vcc
*
st
4
3
Mixer is at:
=
−
915
+
2
2
∗
MHz
st
*
V
-IF of the frontend, the image frequency is quite far away. The image
f
FORWARD
IF
R
*
1
=
4
3
915
=
1220
,
PIN
MHz
−
DIODE
MHz
+
2
*
305
40
=
1525
MHz
TDA5252 G2
Version 1.1
Application
2007-02-26
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