Rainbow Electronics ATA5746 - Manual (Page 6)

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 50 Ω 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 50
Ω
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) 1300
Ω//1.60
433.92 (55 – j216) 900
Ω//1.60
Table 2-2. Input Matching to 50
Ω
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