DS_1x22_017
73M1822/73M1922 Data Sheet
9.1.3 73M1x22 Transmit Spectrum
Figure 27 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.
Also shown, and marked as signaldb(x), is the baseband signal from 1 kHz to 2 kHz. 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.
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 27: Transmit Spectrum to 32 kHz
9.2 Receive Path Signal Processing
9.2.1 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 frequency response and bandwidth of the receive path is dependent on the sampling frequency (Fs).
Figure 28 and Figure 29 show the normalized frequency response of the receive path, including the effect of
the decimation filter in the 73M1902/73M1822 HIC.
For Fs=8 kHz, the 0.2 dB pass-band ripple frequency is from DC to 3.342 kHz. The 3 dB bandwidth is
3.56 kHz.
Rev. 1.6
53
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
