73M1822/73M1922 Data Sheet
DS_1x22_017
9 Signal Processing
9.1 Transmit Path Signal Processing
9.1.1 General Description
In the transmit path, data is first sent by the host DSP through a serial interface to the 73M1822 / 73M1922
then interpolated by a transmit interpolation filter, serialized and transmitted across to the Line-Side Device,
which is floating relative to the Host-Side Device earth ground. The data received on the Line-Side Device
is then de-serialized and digitally sigma-delta modulated to a one-bit data stream of 1.536 Mbps (for a
sample frequency of 8 kHz). The signal is further filtered first by a switched capacitor filter and then a
continuous anti-aliasing circuit.
The frequency response and bandwidth of the transmit path is dependent on the sampling frequency (Fs).
Figure 22 and Figure 23 show the normalized frequency response of the transmit path. For Fs = 8 kHz, the
0.2 dB pass-band ripple frequency is from DC to 3.422 kHz. The 3 dB bandwidth is 3.65 kHz.
9.1.2 Total Transmit Path Response
Transmit Path Overall Frequency Response
10
10
0
10
20
30
40
50
60
70
80
90
100
com
composite(x)
iplo
xo u
xo u
− 100
0
0
1
2
3
4
5
6
7
8
x⋅16
8
Freq(kHz)
Figure 25: Transmit Path Overall Frequency Response to Fs (8 kHz)
Transmit Passband Response
1
1.
0.8
0.6
0.4
0.2
0
composite(x)
0.2
0.4
0.6
0.8
1
− 1.0
0
0.5
1
1.5
2
2.5
3
3.5
4
4
0
x⋅16
Freq(kHz)
Figure 26: Pass-Band Response of the Transmit Path
52
Rev. 1.6
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
