TDA5251F1 View Datasheet(PDF) - Infineon Technologies

Part Name

Description

View to exact match

TDA5251F1

ASK/FSK 315MHz Wireless Transceiver

Infineon Technologies 

TDA5251 F1

Version 1.1

Application

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 1st-IF of the frontend, the image frequency is quite far away. The image

frequency of the receiver is at:

f IMAGE = f SIGNAL + 2 * f IF = 315 MHz + 2 * 105 = 525 MHz

[3 – 5]

The image suppression on the evalboard is about 12dB.

LO-leakage:

The LO of the 1st Mixer is at:

f LO = f RECEIVE

*

4

3

= 315 MHz

*

4

3

= 420 MHz

[3 – 6]

The LO-leakage of the evalboard on the RF-input is about –102dBm.

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 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.

I PIN − DIODE

= VCC − 2 * V FORWARD

R1

, PIN − DIODE

[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

40

2007-02-26

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