hsp50214a Intersil Corporation, hsp50214a Datasheet - Page 20

• Manufacturer Part Number: hsp50214a
• Description: Programmable Downconverter
• Manufacturer: Intersil Corporation

The Cartesian to Polar Coordinate converter accepts I and Q
data and generates magnitude and phase data. The magni-
tude output is determined by the equation:
where the magnitude limits are determined by the maximum
I and Q signal levels into the Cartesian to Polar converter.
Taking fractional 2’s complement representation, magnitude
ranges from 0 to 2.329, where the maximum output is
The AGC loop feedback path consists of an error detector,
error scaling, and an AGC loop filter. The error detector sub-
tracts the magnitude output of the coordinate converter from
FIGURE 21. AGC MULTIPLIER LINEAR AND dB TRANSFER
r
r
=
100
FIGURE 22. AGC GAIN CONTROL TRANSFER FUNCTION
6
5
4
3
2
1
0
=
90
80
70
60
50
40
30
20
10
1.64676
0
0
1.64676 I
0
16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
AGC CONTROL MANTISSA VALUES (TIMES 256)
FUNCTION
1.0
2
+
AGC CONTROL WORD (MANTISSA x 256)
2
64
Q
˙
+
2
.
1.0
˙
2
G (dB)
N = 14
N = 13
N = 12
N = 11
N = 10
N = 15
=
N = 9
N = 8
N = 7
N = 6
N = 5
N = 4
N = 3
N = 2
N = 1
N = 0
1.64676 1.414
128
G (LINEAR)
192
=
2.329
.
(EQ. 15)
HSP50214A
20
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,
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:
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 are
detailed in Table 9.
AGC Loop Gain
AGC Gain Limit
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
is a 4-bit binary value ranging from 0 to 15, and
.
2
25
=
=
-1
M
1
2
+
24
LG
-2
m
2
AGC
–
2
23
2
4
-3
0
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
20
-6
0
1.0
2
19
to 2
-7
+
0.eeeeeeee
-15
2
18
-8
. Together
(EQ. 17A)
2
17
(EQ. 16)
(EQ. 17)
-9
2
16
-10