54
4430-V & VN BPSK/QPSK VME Demodulator & Optional Modulator User’s Manual
Doc: 4430_V,VN.fm, © 11 Jul 2005, 14:55
3.5.17 Register 38h (71h), Loop Capacitor/Input Select
This register selects the demodulator input mode and source as well as the ca-
pacitor used in the loop filter.
Figure 3.5.17
illustrates the breakout of register
bit assignments.
Figure 3.5.17: Register 38h Bit Assignments
Table 3.5.21: Loop Capacitor Input Source/Mode Register Definition
To program this register, follow the procedure below.
1.
First, to select the appropriate loop capacitor value, the value for Eb/No must
be known. This was determined in
Section 3.3
on
page 23
.
2.
This value is then used to select a LPSR value from
Table 3.5.22, “Eb/N0 vs.
Maximum LPSR,” on page 55
.
3.
The LPSR value is then used in calculating the loop bandwidth value from the
formula in
Section 3.3.2
Setup Analysis on page 24
.
Loop Bandwidth (LBW) = LPSR x Symbol Rate
4.
The square root of the demodulator carrier frequency (Demod f
c
) is then
7
6
5
4
3
2
1
0
0/1
-
0/1
0/1
-
0/1
0/1
-
Loop Capacitor Select Bit 1
Loop Capacitor Select Bit 2
Loop Capacitor Select Bit 3
Unused
Unused
Input Source
Input Mode
Unused
Bit No.
Bit Name(s)
Functional Description
07
Unused
Set to zero for proper operation
06
Input Mode
0 - QPSK Mode
1 - BPSK Mode
05
Input Source
0 - Input 1
1 - Input 2
04
Unused
Set to zero for proper operation
03
Unused
Set to zero for proper operation
02-00
Loop Capacitor Select
(See table and calculations to follow)
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