TDA7110 Datasheet, PDF (30/39 Pages) Infineon Technologies AG – ASK/FSK Transmitter 868/433 MHz

TDA7110
Applications
As Figure 3-6 shows, detuning beyond the bandwidth of the matching circuit
results in an increase of the 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 434 MHz. The behaviour at 868 MHz is similar. The
effective load resistance of this circuit is R_L = 250 Ω, which is the optimum
impedance for operation at 3 V. This will lead to a dip of the collector current of
approx. 10%.
16
14
TDA7110
434 MHz / 3V
12
10
8
Is [mA]
Pout [dBm]
6
4
2
0
375
400
425
450
475
500
f [MHz]
Figure 3-6 Output power and collector current vs. frequency
pout_vs_frequ.wmf
C3, L2-C2 and C8 are the main matching components which are used to
transform the 50 Ω load at the SMA-RF-connector to a higher impedance at the
PA-output (250 Ω @ 3 V). L1 can be used for some finetuning of the resonant
frequency but should not become too small in order to keep its losses low.
The transformed impedance of 250+j0 Ω at the PA-output-pin can be verified
with a network analyzer using the following measurement procedure:
1. Calibrate your network analyzer.
2. Connect some short, low-loss 50 Ω 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 refer-
ence 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 outer conductor has to be grounded. Very short connections
have to be used. Do not remove the IC or any part of the matching-compo-
nents!
5. Screw a 50 Ω dummy-load on the RF-I/O-SMA-connector
6. Be sure that your network analyzer is AC-coupled and turn on the power
supply of the IC. The TDA7110 has to be in PLL-Enable-Mode.
7. Measure the S-parameter S11
Wireless Components
3 - 10
Data Sheet, December 2008