MTC-20144TQ-I AMI Semiconductor, Inc., MTC-20144TQ-I Datasheet - Page 6

• Manufacturer Part Number: MTC-20144TQ-I
• Description: Integrated ADSL CMOS Analog Front-End Circuit
• Manufacturer: AMI Semiconductor, Inc.

Analog TX/RX Signals
The reference impedance for all power
calculation is 100 Ω.
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 N large, the signal
can be modelled by a gaussian process
with a certain amplitude probability
density function. Since the maximum am-
plitude 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 (Vpeek/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 trasmitter.
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).
Description
Max level
Max RMS level
Min level
Min RMS level
Description
Max level for receiver
Table 2 : Signal Levels (on the line)
Table 3 : Total Signal Level (on the line)
LT side
RX
839 mVpdif
168 Vrms
54 mVpdif
11 mVrms
LT side
RX
4 Vpdif (Long line)
TX
15.8Vpdif
3.16Vrms
3.95 Vpdif
791mVrms
6
NT side
RX
3.95 Vpdif
791mVrms
42 mVpdif
8 mVrms
NT side
RX
4.2 Vpdif (Short line)
MTC-20144
TX
3.4Vpdif
671mVrms
839mVpdif
168mVrms