L64704 LSI Logic Corporation, L64704 Datasheet - Page 126

• Manufacturer Part Number: L64704
• Description: Satellite Decoder Technical Manual 5/97
• Manufacturer: LSI Logic Corporation

5.7
Automatic Gain
Control (AGC)
5.7.1
ADC Range and
Power
Reference
Figure 5.11
Eye Pattern and
ADC Range
Equation 5.12
5-22
This section describes the L64704’s automatic gain control (AGC) and is
divided into the following subsections:
When the PWR_REF register (Group 4, APR 19) is set to the recom-
mended value of 84, the AGC sets the ratio of the signal range to the
Analog-to-Digital Convertor (ADC) range to 1:1.7 (see
-1.0
-1.7
Assuming that the signal power at the input of the ADC is normalized to
1 V
Q signals). The value of PWR_REF is computed from
where L = 1 if CLK_DR (Group 4, APR 14) = 0 (no internal decimation
filter is used), or L = 4 if CLK_DR = 1 or 2. R is the ADC range. For L = 1
Demodulator Module Functional Description
PWR_REF
1.7
1.0
0.0
Voltage
2
Section 5.7.1, “ADC Range and Power Reference”
Section 5.7.2, “Power Control Loop”
Section 5.7.3, “Power Level”
, the range of the signal (2S) is 2 V (the noise-free level of the I and
=
243 L
-----------------
0.0
R
2
t / Symbol Period
0.5
2 * R = 3.4
Figure
Equation
1.0
5.11).
5.12.
2S =
Input
Signal
Range