Manual

6
4596A–RKE–05/06
ATA5745/ATA5746 [Preliminary]
2.2 Input Matching at LNA_IN
The measured input impedances as well as the values of a parallel equivalent circuit of these
impedances can be seen in Table 2-1. The highest sensitivity is achieved with power matching
of these impedances to the source impedance.
The matching of the LNA input to 50Ω is done using the circuit shown in Figure 2-1 and the val-
ues of the matching elements given in Table 2-2. The reflection coefficients were always
≤ –10 dB. Note that value changes of C1 and L1 may be necessary to compensate individual
board layout parasitics. The measured typical FSK and ASK Manchester-code sensitivities with
a bit error rate (BER) of 10
–3
are shown in Table 2-3 and Table 2-4 on page 7. These measure-
ments were done with wire-wound inductors having quality factors reported in Table 2-2,
resulting in estimated matching losses of 0.8 dB at 315 MHz and 433.92 MHz. These losses can
be estimated when calculating the parallel equivalent resistance of the inductor with
R
loss
=2×π×f × L × Q
L
and the matching loss with 10 log(1+R
In_p
/R
loss
).
Figure 2-1. Input Matching to 50Ω
Table 2-1. Measured Input Impedances of the LNA_IN Pin
f
RF
[MHz] Z
In
(RF_IN) [Ω]R
In_p
//C
In_p
[pF]
315 (72.4 – j298) 1300Ω//1.60
433.92 (55 – j216) 900Ω//1.60
Table 2-2. Input Matching to 50Ω
f
RF
[MHz] C
1
[pF] L
1
[nH] Q
L1
315 2.2 68 20
433.92 2.2 36 15
RF
IN
14
C1
L1
LNA_IN
ATA5745/ATA5746