HSP50214AVC View Datasheet(PDF) - Intersil
Part Name
Description
MFG CO.
'HSP50214AVC' PDF : 60 Pages View PDF
HSP50214A
Automatic Gain Control (AGC)
C0
CN-1
COEFFICIENT
NUMBER
EVEN SYMMETRIC
EVEN TAP FILTER
C0
CN-1
COEFFICIENT
NUMBER
ODD SYMMETRIC
EVEN TAP FILTER
CN-1
C0
COEFFICIENT
NUMBER
EVEN SYMMETRIC
ODD TAP FILTER
CN
C0
COEFFICIENT
NUMBER
ODD SYMMETRIC
ODD TAP FILTER
C0
CN-1
C0
CN-1
COEFFICIENT
NUMBER
ASYMMETRIC
EVEN TAP FILTER
COEFFICIENT
NUMBER
ASYMMETRIC
ODD TAP FILTER
REAL FILTERS
CQ
CQ(0)
CQ(N-1)
COEFFICIENT
NUMBER
CI(N-1)
CI(0)
REAL COEFFICIENT VALUECI
COMPLEX FILTERS
Definitions:
Even Symmetric: h(n) = h(N-n-1) for n = 0 to N-1
Odd Symmetric: h(n) = -h(N-n-1) for n = 0 to N-1
Asymmetric: A filter with no coefficient symmetry.
Even Tap filter: A filter where N is an even number.
Odd Tap filter: A filter where N is an odd number.
Real Filter:
A filter implemented with real coefficients.
Complex Filters: A filter with quadrature coefficients.
FIGURE 20. DEMONSTRATION OF DIFFERENT TYPES OF
DIGITAL FIR FILTERS CONFIGURED IN THE
PROGRAMMABLE DOWNCONVERTER
The AGC Section provides gain to small signals, after the
large signals and out-of-band noise have been filtered out, to
ensure that small signals have sufficient bit resolution in the
Resampling/Interpolating Halfband filters and the Output
Formatter. The AGC can also be used to manually set the
gain. The AGC optimizes the bit resolution for a variety of
input amplitude signal levels. The AGC loop automatically
adds gain to bring small signals from the lower bits of the 26-
bit programmable FIR filter output into the 16-bit range of the
output section. Without gain control, a signal at
20log10(2-12) at the input would have only 4 bits
-72dBfS =
of resolu-
tion at the output (12 bits less than the full scale 16 bits). The
potential increase in the bit resolution due to processing gain
of the filters can be lost without the use of the AGC.
Figure 23 shows the Block Diagram for the AGC Section.
The FIR filter data output is routed to the Resampling and
Halfband filters after passing through the AGC multipliers
and Shift Registers. The outputs of the Interpolating Half-
band filters are routed to the Cartesian to Polar coordinate
converter. The magnitude output of the coordinate converter
is routed through the AGC error detector, the AGC error
scaler and into the AGC loop filter. This filtered error term is
used to drive the AGC multiplier and shifters, completing the
AGC control loop.
The AGC Multiplier/Shifter portion of the AGC is identified in
Figure 23. The gain control from the AGC loop filter is sam-
pled when new data enters the Multiplier/Shifter. The limit
detector detects overflow in the shifter or the multiplier and
saturates the output of I and Q data paths independently.
The shifter has a gain from 0 to 90.31dB in 6.021dB steps,
where 90.31dB = 20log10(2N), when N = 15. The mantissa
provides an additional 6dB of gain in 0.0338dB steps where
6.0204dB = 20log10[1+(X)2-15], where X = 215-1. Thus, the
AGC multiplier/shifter transfer function is expressed as:
AGC Mult/Shift Gain = 2N[1 + (X)2–15 ],
(EQ. 14)
where N, the shifter exponent, has a range of 0>N>15 and
X, the mantissa, has a range of 0>X>(215-1).
Equation 14 can be expressed in dB,
(AGC Mult/Shift Gain)dB = 20log10(2N[1 + (X)2-15 ] ) (EQ. 14A)
The full AGC range of the Multiplier/Shifter is from 0 to
96.331dB (20log10[1+(215-1)2-15] + 20log10[215] = 96.331).
Figure 21 illustrates the transfer function of the AGC multi-
plier versus mantissa control for N = 0. Figure 22 illustrates
the complete AGC Multiplier/Shifter Transfer function for all
values of exponent and mantissa control.
The resolution of the mantissa was increased to 16 bits in
the A Version, to provide a theoretical AM modulation level of
-96dBc (depending on loop gain, settling mode and SNR).
This effectively eliminates AM spurious caused by the AGC
resolution.
For fixed gain, either set the upper and lower AGC limits to
the same value, or set the limits to minimum and maximum
gains and set the AGC gain to zero.
19
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