hsp50214a Intersil Corporation, hsp50214a Datasheet - Page 22

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

Using AGC loop gain, the AGC range, and expected error
detector output, the gain adjustments per output sample for
the Loop Filter Section of the Digital AGC can be given by
The loop gain determines the growth rate of the sum in the
loop accumulator which, in turn, determines how quickly the
AGC gain traces the transfer function given in Figures 21
and 22. Since the log of the gain response is roughly linear,
the loop response can be approximated by multiplying the
maximum AGC gain error by the loop gain. The expected
AGC Slew Rate
†
IFIR
QFIR
SERIAL
Controlled via microprocessor interface.
OUT
P
16
16
26
26
=
1.5dB THRESH
M
MSB = 0
LG
MSB = 0
2
4
–
4
18
EXP=2
AGC MULTIPLIER/SHIFTER
18
2
–
15 E
NNNN
13
AGC LOOP FILTER
–
–
MAG*1.64676
LG
16
MANTISSA =
01.XXXXXXXXXXXXXX
LIMIT
DET
FIGURE 23. AGC BLOCK DIAGRAM
LOWER LIMIT
LIMIT
DET
UPPER LIMIT
(EQ. 18)
HSP50214A
LIMIT
DET
+
IAGC
18
QAGC
(RANGE = 0 TO 2.18344)
18
22
†
†
range for the AGC rate is ~ 0.00004 to 1.23dB/symbol time
for a threshold of 1/2 scale. See the notes at the bottom of
Table 9 for calculation of the AGC response times. The max-
imum AGC Response is given by:
Since the AGC error is scaled to adjust the gain, the loop
settles asymptotically to its final value. The loop settles to
the mean of the signal.
AGC Response
INTERPOLATING
RESAMPLING
AGCGNSEL
FIR FILTERS
HALFBAND
13
FILTERS
AND
AGC ERROR SCALING
MANTISSA
Max
Loop Gain)(AGC Output Weighting)
=
Input(Cart/Polar Gain)(Error Det Gain) AGC
(RANGE = 0 TO 1)
4
(RANGE = 0 TO 2.3)
EXP
MAGNITUDE
4
COORDINATE
CONVERTER
(G = 1.64676)
CARTESIAN
POLAR
TO
DETECTOR
ERROR
AGC
13
(EQ. 19)