L64780 LSI Logic Corporation, L64780 Datasheet - Page 24

• Manufacturer Part Number: L64780
• Description: Dvb-t Cofdm Demodulator Technical Manual 2/00
• Manufacturer: LSI Logic Corporation

2.3.3 AGC Loop Gain K
2-6
The gain of the loop, K
Equation 2.3
where:
With an RMS value of
the loop gain is:
Equation 2.4
To code K
LSI Logic uses the AGC_GAIN[2:0] register, with the following
correspondence:
Equation 2.5
Because the number of values AGC_GAIN can have is limited, so are
those of K
Equation 2.6
In our example, AGC_GAIN = 4 is the most appropriate value, giving a
value of:
Equation 2.7
The real-to-complex block takes the input samples from the ADC output
and converts them into a complex baseband representation for input to
the FFT block.
Architectural Overview
F is the slope of the tuner AGC characteristics in dB/V.
T
is the target value for the input signal.
s
s
s
, LSI Logic uses an approximation to the nearest power of 2.
. Thus,
K
K
AGC_GAIN
K
K
s
s
s
s
=
=
1.52 10
2
8.5 10
--------------------------
–
7.5 10
8
s
F
, must obey the following rule:
–
=
2 AGC_GAIN
0.283
T
–
–
–
5
5
-------------- - 4
2
log
6
log
, and a tuner characteristic of 50 dB/V,
K
2
s
–