L64780 LSI Logic Corporation, L64780 Datasheet - Page 22

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

2.2 Analog-to-Digital Converter (ADC)
2.3 Automatic Gain Control (AGC)
2.3.1 AGC Target RMS Value
Figure 2.2
2-4
2
b
-1
8
2
-2
b
Structure of 9-Bit AGC_TARGET Register
AGC_TARGET_MSB[5:0]
7
Features of the L64780 analog-to-digital converter include:
The L64780 also offers a 10-bit parallel port for connection to an
external, 10-bit ADC.
The Tuner AGC Amplifier amplifies the signal. The resulting signal has
an RMS value of
allows the FFT to work properly. To do this, the input signal power must
be 10.95 dB down on the maximum ADC input range, normalized to 1.0.
This means the RMS value of the input to the L64780 is:
Figure 2.2
For the FFT to perform correctly, the input level of the COFDM signal
must be 10.95 dB down on the normalized 1.0 Input Range. Thus, the
target RMS value, , of the input signal must be 0.283, as shown in
Equation 2.1.
Equation 2.1
Architectural Overview
2
b
low-IF center frequency input: 4.57 MHz
input bandwidth: 8 MHz
sampling clock: 18.29 MHz
resolution: 8-bit
-3
6
defines The nine-bit AGC_TARGET register.
2
b
-4
5
T
0
=
T
. The AGC amplifies this signal so that its variance
b
2
-5
4
512
2
-- -
b
2
3
-6
b
2
-7
2
AGC_TARGET_LSB[5:0]
b
2
1
-8
2
b
-9
0
0
=
0.283
.