參數(shù)資料
型號: STA400A
廠商: 意法半導(dǎo)體
英文描述: XMRADIO SDARS CHANNEL DECODER
中文描述: XMRADIO衛(wèi)星數(shù)字收音機信道解碼器
文件頁數(shù): 16/117頁
文件大小: 910K
代理商: STA400A
STA400A
16/117
Figure 9. RRC Filter Passband Ripple
Carrier Phase/Frequency Error Detector
The carrier Phase/Frequency Error Detector (PFD) measures the error between the sampled symbols and the
quadrant bisector. The error is calculated by the following formula : PH
err
= I x Sgn(Q) - Q x Sgn(I), where Sgn(.)
is the sign function.
This value is computed at symbol rate if the actual I and Q components are greater than a programmed thresh-
old otherwise the previous value is maintained. In this way the detector outputs a DC value proportional to the
frequency offset between the incoming signal and the local oscillator. In the steady state, when the carrier loop
is locked (and, therefore, the phase error is small), the circuit behaves like a pure phase detector while during
the acquisition phase it behaves like a PFD.
The threshold value may be programmed by the PFDTHR register. The signal level after the AGC2 loop must
be taken into account when setting the threshold. The default preset for this parameter is about the 20% of the
AGC2 reference value (see AGC2REF register).
The carrier Phase and Frequency Detector Gain (K
d
) characteristic as a function of the Carrier to Noise ratio is
given in fig.10. K
d
= 1.24 is the value for a noise free input signal and may be reduce up to 50% of its maximum
value in a low C/N condition.
Figure 10. Carrier Phase/Frequency Detector Gain
0
100
200
300
400
500
600
700
800
900
1000
1
0.5
0
0.5
Frequency (kHz)
M
0
2
4
6
8
10
12
14
16
18
20
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
C/N (dB)
PFD Gain
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