73M1866B/73M1966B Data Sheet
DS_1x66B_001
8.6.3 73M1x66B Transmit Spectrum
Figure 28 shows the transmit spectrum observed on the line from dc to 32 kHz for a sample frequency
(Fs) of 8 kHz. The transmit signal is band-limited (by default) to Fs/2=4 kHz and is flat (with 0.2 dB ripple)
to 3.65 kHz and is marked as Txdb(x) in the figure. All frequencies double for a 16 kHz sample rate
Also shown, and marked as signaldb(x), is the baseband signal from 1 kHz to 2 kHz for an 8 kHz sample
rate (2 kHz to 4 for a 16 kHz sample rate). The aliases of signaldb(x) are shown as aliasdb(x) and are
attenuated significantly with better than 80 dB attenuation at 8 kHz, better than 60 dB at 16 kHz, better
than 100 dB at 24 kHz, etc for an 8 kHz sample rate and the frequencies double for a 16 kHz sample rate.
Transmit Spectrum
20
20
0
20
signaldb(x)
aliasdb(x)
Txdb(x)
40
60
80
100
120
140
− 140
0
0
4
8
12
16
20
24
28
32
32
16x
Freq
Figure 28: Transmit Spectrum to 32 kHz for an 8 kHz Sample Rate
8.7 Receive Path Signal Processing
8.7.1 General Description
In the receive path, the signal from the telephone line is input to the anti-aliasing filter and passed through
a selectable low pass (notch) filter, which can be used to attenuate in-band Billing Tones. The analog
signal is digitized by a sigma-delta analog to digital converter. The resulting high frequency one-bit data
stream is decimated and sent to the Host-Side Device via the barrier. Another decimation FIR filter in the
Host-Side Device filters the received data and sends it to the host DSP for processing.
The response of the receive path, in conjunction with the decimation filter in the Host-Side Device,
provides a flat pass-band response to 3.342 kHz at an 8 kHz sample rate or 6.744 kHz with a 16 kHz
sample rate with 0.2 dB ripple. The 3 dB bandwidth is 3.58 kHz at 8kHz sample rate or 7.226 kHz at a
16 kHz sample rate. . The one-bit data stream is 1.536 Mbps for an 8 kHz sample rate or 3.072 Mbps
with a 16 kHz sample rate.
50
Rev. 1.6
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
