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TDA18218HN Datasheet PDF : 25 Pages
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NXP Semiconductors
TDA18218HN
DVB-T Silicon Tuner IC
and 8 MHz channel bandwidths). The TDA18218HN requires a single 16 MHz crystal for
clock generation, a 16 MHz differential sine wave clock reference is available to drive a
channel decoder.
8.1 AGC1 stage
The TDA18218HN embeds 2 different RF amplifiers with internal gain control.
The first stage, AGC1, behaves like a LNA (Low noise amplifier); its gain can take 4
different values (15 dB, 12 dB, 9 dB and 6 dB). Purpose of this amplifier is to ensure a low
noise figure for the tuner.
In order to optimize noise and linearity performances an internal level detector selects the
appropriate gain:
• If the signal level at the tuner is low, the gain is set to the maximum value (15 dB).
• If the signal level at the tuner input is high, the gain is set to the minimum value (6 dB).
• In between the gain is set to an intermediate value 12 dB or 9 dB.
The strategy of the level detection is a proprietary algorithm from NXP, managed by the
driver.
It should be noted that:
1. The level detector measures the signal level within the complete RF frequency range,
i.e. from 50 MHz to 870 MHz. Consequently, AGC1 gain is adapted to the complete
RF power. If a strong signal is present at the tuner input, it will determine AGC1 gain
(even if it is not the wanted signal). This concept prevents the tuner from overloading.
2. The level control is always operating.
8.2 AGC2 stage
The second stage, AGC2, is also an amplifier with a gain controlled thanks to a level
detector.
The gain is controlled between −12 dB and +16.4 dB, it is adapted by steps of 0.2 dB.
It should be noted that:
1. The level control is always operating. Consequently, this amplifier is responsible for
adapting the daily level changes.
2. The level detector measures the signal level within the complete RF frequency range
(same as AGC1)
The strategy of the level detection is a proprietary algorithm from NXP, managed by the
driver.
8.3 IF AGC
Finally, in order to adapt the tuner output level, a last amplifier is used (IF AGC). This
amplifier delivers the appropriate level to the DVB-T channel decoder. The output level is
therefore controlled thanks to the DC voltage applied on VIFAGC pin. This voltage is
commonly delivered by the channel decoder.
TDA18218HN_1
Product data sheet
Rev. 01 — 8 July 2009
© NXP B.V. 2009. All rights reserved.
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