tda5251f1 Infineon Technologies Corporation, tda5251f1 Datasheet - Page 40

• Manufacturer Part Number: tda5251f1
• Description: Ask/fsk 315mhz Wireless Transceiver
• Manufacturer: Infineon Technologies Corporation

Confidential
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 12dB.
LO-leakage:
The LO of the 1
The LO-leakage of the evalboard on the RF-input is about –102dBm.
3.1.3
The evalboard can be set into the TX-Mode by grounding the RX/TX-jumper on the evalboard or
programming the TDA5251 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.
Preliminary Specification
I
f
PIN
LO
f
IMAGE
-
=
DIODE
f
RECEIVE
Switch in TX-Mode
=
=
V
st
f
CC
SIGNAL
Mixer is at:
*
-
4
3
2
*
=
V
315
FORWARD
st
-IF of the frontend, the image frequency is quite far away. The image
+
MHz
2
R
1
*
*
f
,
IF
4
3
PIN
=
-
=
420
DIODE
315
MHz
MHz
+
2
40
*
105
=
525
MHz
TDA5251 F1
Version 1.0
Application
2003-02-18
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