HSP50214 데이터 시트보기 (PDF) - Intersil
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HSP50214 Datasheet PDF : 54 Pages
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HSP50214
the programmable AGC THRESHOLD value. The bit weight-
ing of the AGC THRESHOLD value (Control Word 8, bits 16-
28) is shown in Table 5. Note that the MSB is always zero.
The range of the AGC THRESHOLD value is 0 to 7.9995.
The AGC Error Detector output has the identical range.
TABLE 5. AGC THRESHOLD (CONTROL WORD 8) BIT
WEIGHTING
28 27 26 25 24 23 22 21 20 19 18 17 16
22 21 20. 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10
The loop gain is set in the AGC Error Scaling circuitry, using
the two programmable mantissas and exponents. The man-
tissa, M, is a 4-bit value which weights the loop filter input
from 0.0 to 0.9375. The exponent, E, defines a shift factor
that provides additional weighting from 20 to 2-15 Together
the mantissa and exponent define the loop gain as given by,
AGC Loop Gain = MLG2–4 2–(15 – ELG)
(EQ. 16)
where MLG is a 4-bit binary value ranging from 0 to 15, and
ELG is a 4-bit binary value ranging from 0 to 15. Table 7 and
8 detail the binary values and the resulting scaling effects of
the AGC Scaling mantissa and exponent. The composite
(shifter and multiplier) AGC scaling Gain range is from
0.0000 to 2.329(0.9375)20 = 0.0000 to 2.18344. The scaled
gain error can range (depending on threshold) from 0 to
2.18344, which maps to a “gain change per sample” range
of 0 to 3.275dB/sample.
The AGC Gain mantissa and exponent values are pro-
grammed into Control Word 8, bits 0-15. The PDC provides
for the storing of two values of AGC Scaling Gain (both expo-
nent and mantissa). This allows for quick adjustment of the
loop gain by simply asserting the external control line
AGCGNSEL. When AGCGNSEL = 0, then AGC GAIN 0 is
selected, and when AGCGNSEL = 1, AGC Loop Gain 1 is
selected. Possible applications include acquisition/tracking,
no burst present/burst present, strong signal/weak signal,
track/hold, or fast/slow AGC values.
The AGC loop filter consists of an accumulator with a built in
limiting function. The maximum and minimum AGC gain lim-
its are provided to keep the gain within a specified range and
are programed by 12-bit control words using the following
the equation:
AGC Gain Limit = (1 + mAGC2–9)2e
(EQ. 17)
(AGC Gain Limit)dB = (6.02)(eeee) + 20log(1.0 + 0.eeeeeeee)
(EQ. 17A)
where m is an 8-bit mantissa value between 0 and 511, and e
is the 4-bit exponent ranging from 0 to 15. Control Word 9, bits
16-27 are used for programming the upper limit, while bits 0-
11 are used to program the lower threshold. The ranges and
format for these limit values are shown in Tables 6A - C. The
bit weightings for the AGC Loop Feedback elements is
detailed in Table 9.
TABLE 6A. AGC LIMIT EXPONENT vs GAIN
GAIN(dB)
EXPONENT
MANTISSA
96.330
15
511
90.309
15
0
84.288
14
0
78.268
13
0
72.247
12
0
66.227
11
0
60.206
10
0
54.185
9
0
48.165
8
0
42.144
7
0
36.124
6
0
30.103
5
0
24.082
4
0
18.062
3
0
12.041
2
0
6.021
1
0
0.000
0
0
TABLE 6B. AGC LIMIT MANTISSA vs GAIN
GAIN(dB)
EXPONENT
MANTISSA
6.000
0
509
5.750
0
480
5.500
0
452
5.250
0
425
5.000
0
398
4.750
0
372
4.500
0
347
4.250
0
323
4.000
0
299
3.750
0
276
3.500
0
254
3.250
0
232
3.000
0
211
2.750
0
190
2.500
0
170
2.250
0
151
2.000
0
132
1.750
0
114
1.500
0
96
1.250
0
79
1.000
0
62
0.750
0
46
0.500
0
30
0.250
0
14
0.020
0
1
TABLE 6C. AGC LIMIT DATA FORMAT
CONTROL WORD 9 BIT: 27 26 25 24 23 22 21 20 19 18 17 16
FORMAT e
e
e
e
m
m
m
m
m
m
m
m
19
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