MTC20154-TQ-C2 ST Microelectronics, Inc., MTC20154-TQ-C2 Datasheet - Page 8

• Manufacturer Part Number: MTC20154-TQ-C2
• Description: Integrated Adsl CMOS Analog Front-end Circuit
• Manufacturer: ST Microelectronics, Inc.

MTC20154
Analog TX/RX Signals
The reference impedance for all power calculations is 100Ω.
DMT Signal
A DMT signal is basically the sum of N independently QAM modulated signals, each carried over a distinct
carrier. The frequency separation of each carrier is 4.3125 KHz with a total number of 256 carriers (ANSI).
For large N, the signal can be modelled by a gaussian process with a certain amplitude probability density
function. Since the maximum amplitude is expected to arise very rarely, the signal is clipped to trade-off
the resulting SNR loss against AD/DA dynamic range.
A clipping factor (Vpeak/Vrms = ”crest factor”) of 5 is used resulting in a maximum SNR of 75 dB. ADSL
DMT signals are nominally sent at -40 dBm/Hz +/- 3 dB (-3.65 dBm/carrier) with a maximal power of 100
mW for downlink transmitter and 4.5 mW for uplink transmitter.
The minimum SNR+D needed for DMT carrier demodulation is about (3*N+20) dB with a minimum of 38
dB where N is the constellation size of a carrier (in bits).
Table 7. Signal Levels (on the line)
Table 8. Total Signal Level (on the line)
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Max level
Max RMS level
Min level
Min RMS level
Max level for receiver
Description
Description
839 mVpdif
168 Vrms
54 mVpdif
11 mVrms
4 Vpdif (Long line)
RX
LT side
LT side
15.8 Vpdif
3.16 Vrms
3.95 Vpdif
791 mVrms
RX
TX
3.95 Vpdif
791 mVrms
42 mVpdif
8 mVrms
4.2 Vpdif (Short line)
RX
NT side
NT side
RX
671 mVrms
839 mVpdif
3.4 Vpdif
168 mVrms
TX