Rainbow Electronics ATA5812 - Manual (Page 10)

10
ATA5811/ATA5812 [Preliminary]
4689B–RKE–04/04
Input Matching at RF_IN The measured input impedances as well as the values of a parallel equivalent circuit of
these impedances can be seen in Table 1. The highest sensitivity is achieved with
power matching of these impedances to the source impedance of 50
Ω
The matching of the LNA Input to 50
Ω
was done with the circuit according to Figure 7
and with the values given in Table 2. The reflection coefficients were always
≤
10 dB.
Note that value changes of C
1
and L
1
may be necessary to for compensate individual
board layouts. The measured typical FSK and ASK Manchester code sensitivities with a
Bit Error Rate (BER) of 10
-3 are shown in Table 3 on page 11 and Table 4 on page 11.
These measurements were done with inductors having a quality factor according to
Table 2, resulting in estimated matching losses of 1.0 dB at 315 MHz, 1.2 dB at
433.92 MHz and 0.6 dB at 868.3 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
p
/R
loss
).
With an ideal inductor, for example, the sensitivity at 433.92 MHz/FSK/20 kBaud/
±16 kHz/Manchester can be improved from -106 dBm to -107.2 dBm. The sensitivity
depends on the control logic which examines the incoming data stream. The exami-
nation limits must be programmed in control registers 5 and 6. The measurements in
Table 3 on page 11 and Table 4 on page 11 are based on the values of registers 5 and
6 according to Table 39 on page 57.
Figure 7. Input Matching to 50
Ω
Table 1. Measured Input Impedances of the RF_IN Pin
f
RF
/MHz Z(RF_IN) R
p
//C
p
315 (44-j233)
Ω
1278
Ω
//2.1 pF
433.92 (32-j169)
Ω
925
Ω
//2.1 pF
868.3 (21-j78)
Ω
311
Ω
//2.2 pF
Table 2. Input Matching to 50
Ω
f
RF
/MHz C
1
/pF L
1
/nH Q
L1
315 2.2 56 43
433.92 1.8 27 40
868.3 1.2 6.8 58
ATA5811/ATA5812
RF_IN
4
RF
IN
C
1
L
1