TDA5251F1 Datasheet, PDF (44/88 Pages) Infineon Technologies AG – ASK/FSK 315MHz Wireless Transceiver

TDA5251 F1
Version 1.0
Confidential
Application
As Figure 3-8 shows, detuning beyond the bandwidth of the matching circuit results in a significant
increase of collector current of the power amplifier and in some loss of output power. This diagram
shows the data for the circuit of the test board at the frequency of 315MHz. The effective load
resistor of this circuit is RL= 250Ohm, which is the optimum impedance for operation at 3V. This will
lead to a dip of the collector current of approx. 20%.
pout_vs_frequ_315.wmf
Figure 3-8 Power output and collector current vs. frequency
C4, L2 and C3||C2 are the main matching components which are used to transform the 50 Ohm
load at the SMA-RF-connector to a higher impedance at the PA-output (250Ohm@3V). L1 can be
used for finetuning of the resonance frequency but should not be too low in order to keep its loss
low.
The transformed impedance of 250Ohm+j0 at the PA-output-pin can be verified with a network
analyzer using this measurement procedure:
1. Calibrate your network analyzer.
2. Connect a short, low-loss 50 Ohm cable to your network analyzer with an open end on one side.
Semirigid cable works best.
3. Use the „Port Extension“ feature of your network analyzer to shift the reference plane of your
network analyzer to the open end of the cable.
4. Connect the center-conductor of the cable to the solder pad of the pin „PA“ of the IC. The shield
has to be grounded. Very short connections must be used. Do not remove the IC or any part of
the matching-components!
5. Screw a 50Ohm-dummy-load on the RF-I/O-SMA-connector
6. The TDA5251 has to be in ASK-TX-Mode, Data-Input=LOW.
7. Be sure that your network analyzer is AC-coupled and turn on the power supply of the IC.
8. Measure the S-parameter
Preliminary Specification
44
2003-02-18