TLC32044C_11 Datasheet, PDF (29/39 Pages) Texas Instruments – VOICE-BAND ANALOG INTERFACE CIRCUITS

TLC32044C, TLC32044E, TLC32044I, TLC32044M, TLC32045C, TLC32045I
VOICE-BAND ANALOG INTERFACE CIRCUITS
SLAS017F − MARCH 1988 − REVISED MAY 1995
(sin x)/x roll-off for a zero-order hold function
The (sin x) / x roll-off for the AIC DAC zero-order hold function at a band-edge frequency of 3000 Hz for the
various sampling rates is shown in the table below.
Table 4. (sin x)/x Roll-Off
f_s (Hz)
20 log ^{sin π f/f}s
π f/f_s
(f = 3000 Hz)
(dB)
7200
8000
9600
14400
19200
− 2.64
− 2.11
− 1.44
− 0.63
− 0.35
The actual AIC (sin x)/ x roll-off will be slightly less than the above figures because the AIC has less than a 100%
duty cycle hold interval.
correction filter
To compensate for the (sin x)/ x roll-off of the AIC, a first-order correction filter (shown below) is recommended.
u_{(i + 1)}
+
+
(1 − p1)P2
z−1
y_{(i + 1)}
p1
The difference equation for this correction filter is:
yi + 1 = p2(1 − p1) (u_{i + 1}) + p1 yi
where the constant p1 determines the pole locations.
The resulting squared magnitude transfer function is:
|H(f)|2
+
p22 (1–p1)2
1 – 2p1 cos(2 p fńfs) )
p12
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