cx24118a NXP Semiconductors, cx24118a Datasheet - Page 16

• Manufacturer Part Number: cx24118a
• Description: Advanced Modulation Digital Satellite Tuner
• Manufacturer: NXP Semiconductors

NXP Semiconductors
2.3
CX24118A_N_2
Product data sheet
Gain Settings
variable gain baseband amplifier section provides further amplification. The baseband
section includes a servo loop, which eliminates DC offset variations at the output. The
baseband amplifier section also includes a filter with finer bandwidth control between 2 MHz
and 65 MHz. The filter is optimized to provide stop band attenuation for anti-alias filtering and
adjacent channel performance.
The CX24118A is controlled by a single AGC signal, providing a dynamic range of 90 dB.
The gain stages include an LNA (Low Noise Amplifier) and VCA (Voltage Controlled
Attenuator), VGA1 (Variable Gain Amplifier 1), VGA2, and a final amplifier. These gain
stages are shown in figure 2-1.
The gain and offset of the different stages can be adjusted to provide the best overall IP3 and
Noise Figure performance over input power. To optimize the performance at both high and
low powers, split gain settings are recommended. This involves estimating the input power in
order to select the best set of gain settings. The maximum signal level settings given in
Table 2
other carriers within the satellite frequency range. The minimum signal level settings given in
Table 3
carriers within the satellite frequency range does not exist. The transition point between the
minimum signal level settings and the maximum signal level settings is set at P
dBm.
Table 2.
RFVCAOff[1:0]
BBVGA2Off[2:0]
BBVGA1Off[2:0]
BBAmpGain[3:0]
FOOTNOTES:
(1)
This value is valid for the CX24116, CX24126, and CX24114 demodulators. For the CX24123
demodulator, use the setting that corresponds to 25 dB.
Parameter
should be used when the input power is high while there is significant power from
should be used when the input power is low or when significant power from other
Maximum Signal Level Settings
Rev. 02 — 8 September 2009
0x20[3:2]
0x1F[5:3]
0x1F[2:0]
0x1D[3:0]
Register Location
Register Setting
0011b
111b
111b
00b
Chapter 2: Functional Descriptions
CX24118A
Meaning
31 dB
-70 dB
-27 dB
-22 dB
© NXP B.V. 2009. All rights reserved.
(1)
threshold
= -50
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