ML2021IP Просмотр технического описания (PDF) - Fairchild Semiconductor
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ML2021IP Datasheet PDF : 11 Pages
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PRODUCT SPECIFICATION
ML2021
Functional Description
The ML2021 consists of a continuous anti-alias filter, three
programmable switched capacitor equalization filters, an
output smoothing filter, an output driver, and a digital section
for the serial interface.
Anti-Alias Filter
The first section is a continuous anti-alias filter. This filter is
needed to prevent aliasing of high frequency signal present
on the input into the passband by the sampling action of the
switched capacitor filters. This section is a continuous sec-
ond order lowpass filter with a typical 3 dB frequency at 20
kHz and 30 dB of rejection at 124 kHz.
Equalization Filters
The programmable filters implement a family of frequency
response curves intended to compensate for the response of
telephone lines.
This filter is composed of three distinct sections: slope,
height, and bandwidth.
Response of Slope, Height, and Bandwidth
The family of response curves generated by the slope section
are shown in Figures 2 and 3. There are 4 slope select bits,
S3-S0. These bits alter the slope of the highpass response
under 1000Hz, and as a result, the absolute gain above 1000
Hz will be unique for each setting. Table 1 gives typical 1
kHz gain values for all slope settings.
Table 1. Typ. 1kHz Gain for Slope Settings
Slope
Setting
Rel 1kHz Gain (dB)
NL/L = 1
NL/L = 0
0
0.0
REL
1
0.4
1.4
2
0.9
2.6
3
1.4
3.7
4
1.8
4.7
5
2.3
5.5
6
2.8
6.3
7
3.4
7.2
8
3.7
7.8
9
4.2
8.4
10
4.6
9.0
11
5.0
9.5
12
5.4
10.0
13
5.8
10.5
14
6.2
11.0
15
6.6
11.4
HT, BW Bits = 0
There is an additional bit, NL/L, that also affects the high-
pass response of the slope filter. The slope response curves in
Figure 2 are with NL/L = 0. These same response curves are
shown in Figure 3 with NL/L = 1. Notice that the NL/L bit
adds more droop in the highpass response below 2500 Hz.
The family of response curves generated by the height sec-
tion are shown in Figure 4. There are 4 height select bits,
H3-H0. This section creates a peak in the response at 3250
Hz and this filter controls the amount of peaking. Table 2
gives typical 1 kHz gain values for all height and bandwidth
settings.
Table 2. Typ. 1kHz Gain for HT and BW Settings
Relative 1kHz Gain (dB)
HT Setting
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0 Rel 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
10000000000000000
20000000000000000
30000000000000000
4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.1
5 0 0 0 0 0 0 0 0 0 0 0 0 0.1 0.1 0.1 0.1
6 0 0 0 0 0 0 0 0 0 0 0.1 0.1 0.1 0.1 0.1 0.1
7 0 0 0 0 0 0 0 0 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2
8 0 0 0 0 0 0 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.3 0.3 0.4
9 0 0 0 0 0 0.1 0.1 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.5 0.6
10 0 0 0 0 0.1 0.1 0.1 0.1 0.2 0.3 0.3 0.4 0.5 0.6 0.7 0.8
11 0 0 0 0.1 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 0.7 0.8 0.9 1.1
12 0 0 0.1 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.7 0.8 1.0 1.1 1.4 1.6
13 0 0 0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.8 0.9 1.1 1.4 1.6 1.9 2.3
14 0 0 0.1 0.1 0.2 0.3 0.4 0.5 0.7 0.8 1.0 1.2 1.5 1.7 2.0 2.4
15 0 0 0.1 0.1 0.2 0.3 0.4 0.5 0.7 0.9 1.1 1.3 1.6 1.8 2.1 2.5
Slope Bits = 0
The family of response curves generated by the bandwidth
section is shown in Figure 5. There are 4 bandwidth select
bits, B3-B0. This section causes the response of the 3250 Hz
peak to be widened, and as a result, this filter controls the
bandwidth of the 3250 Hz peaked region.
Transfer Function
The transfer function for the ML2021 is shown below. This
transfer function is valid for magnitude response only. The
actual magnitude response from an individual device may
deviate from the computed response from the transfer func-
tion by typically 0–0.2 dB.
H(s) = -bc---((--s-s----++-----bc---)-) × [--[-s--s-2--2+--+---h--(--(-ω-ω---o--o--⁄--⁄-Q-Q----)-)-s--s--+--+---ω--ω---o-o-2-2--]--] × -[--s---i-(-n--π--(-f-π--⁄-f--f-c⁄---f-)-c---)---]
s = j × 256000 × tan (πf/128000)
ωo = 20463.77
fc = 128000
b,c : See Table 3.
(slope)
Q : See Table 4.
(bandwidth)
h : See Table 5.
(height)
REV. 1.1.1 3/19/01
7
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