Datasheet

73M1866B/73M1966B Data Sheet DS_1x66B_001
48 Rev. 1.6
8.5 Transmit and Receive Levels
8.5.1 A-Law
According to the ITU-T Recommendation G.711, A-law assumes +4096 (in sign plus 12 bit) to represent
3.14 dBm. That is, a sinusoid having a peak value of +4095 to correspond to +3.14 dBm or 1.1119 Vrms
or 1.5725 Vpk or 3.145 Vpp.
Figure 24 shows the mapping implied in the ITU-T Recommendation G.711. Therefore, one least
significant bit in 16-bit code is equivalent to:
bitV
V
LSB /0.48
8
2
5725.1
15
µ =
−
=
A-Law (Sign + 12 bits)
16 bits Linear
0 1 1 1 11 1 1 1 1 1 1 1
0 1 1 1 11 1 1 1 1 1 1 1
0
0
0
Figure 24: Mapping of A-law Code to 16-bit Code
For A-law, 0 dBm=774.6 mVrms=1.095 Vp (sinusoid) implies a peak code of 22,821=5925h.
8.5.2 μ-Law
Similarly, μ-Law assumes +8159 (in sign plus 13 bit) to represent 3.17 dBm. That is, a sinusoid having a
peak value of +8159 to correspond to +3.17 dBm or 1.1157 Vrms or 1.578 Vpk or 3.156 Vpp.
Figure 25 shows the mapping implied in the ITU-T Recommendation G.711. Therefore, one least
significant bit in 16-bit code is equivalent to:
bitV
V
LSB /35.48
32636
578.1
µ ==
u-Law (Sign + 13 bits)
16 bits Linear
0 1 1 1 1 1 1 1 0 1
0 1 1 1 1 1 1 1 0 1 1 1 1
1
0
0
1 1 11
Figure 25: Mapping of μ-law Code to 16-bit Code
For μ-law, 0 dBm=774.6 mVrms=1.095 Vp (sinusoid) implies a peak code of 22,647=5876h.
8.5.3 Transmit and Receive Level Control
The 73M1x66B provides digital and analog control over the gains of transmit and receive signal. The
overall transmit gain adjustment is +13.4 dB to –26 dB and the range of the receiver gain is +10.4 dB to
–24 dB. Both gain adjustments are in steps of 0.125 dB. Optimal performance on how the overall gain is
to be achieved requires the appropriate management of the gain elements in the signal paths.