hsp50214 Intersil Corporation, hsp50214 Datasheet - Page 19

• Manufacturer Part Number: hsp50214
• Description: Programmable Downconverter
• Manufacturer: Intersil Corporation

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
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 2
the mantissa and exponent define the loop gain as given by,
AGC Loop Gain
where M
E
8 detail the binary values and th
the AGC Scaling mantissa and exponent. The composite
(shifter and multiplier) AGC scaling Gain range is from
0.0000 to 2.329(0.9375)
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
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.
AGC Gain Limit dB = 6.02 eeee
28
2
LG
2
is a 4-bit binary value ranging from 0 to 15. Table 7 and
27
2
1
LG
WEIGHTING
2
26
0
CONTROL WORD 9 BIT:
is a 4-bit binary value ranging from 0 to 15, and
.
2
25
=
=
-1
M
1
2
24
LG
+
-2
m
2
AG C
–
2
23
2
4
-3
0
FORMAT
2
= 0.0000 to 2.18344. The scaled
2
–
–
2
22
9
15 E
-4
2
–
e
e
2
+
21
resulting scaling effects of
LG
-5
20
log
2
27
20
e
-6
1.0
0
2
19
to 2
TABLE 6C. AGC LIMIT DATA FORMAT
-7
+
26
e
0.eeeeeeee
2
18
-15
-8
(EQ. 17A)
Together
2
17
(EQ. 16)
(EQ. 17)
25
-9
e
HSP50214
2
16
-10
24
e
19
23
m
GAIN(dB)
GAIN(dB)
96.330
90.309
84.288
78.268
72.247
66.227
60.206
54.185
48.165
42.144
36.124
30.103
24.082
18.062
12.041
6.021
0.000
6.000
5.750
5.500
5.250
5.000
4.750
4.500
4.250
4.000
3.750
3.500
3.250
3.000
2.750
2.500
2.250
2.000
1.750
1.500
1.250
1.000
0.750
0.500
0.250
0.020
TABLE 6A. AGC LIMIT EXPONENT vs GAIN
TABLE 6B. AGC LIMIT MANTISSA vs GAIN
22
m
21
m
EXPONENT
EXPONENT
20
m
15
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
19
m
18
m
MANTISSA
MANTISSA
17
m
511
509
480
452
425
398
372
347
323
299
276
254
232
211
190
170
151
132
114
96
79
62
46
30
14
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
16
m