sin

TLC32044C, TLC32044E, TLC32044I, TLC32044M, TLC32045C, TLC32045I

VOICE-BAND ANALOG INTERFACE CIRCUITS

SLAS017F − MARCH 1988 − REVISED MAY 1995

29

POST OFFICE BOX 655303

(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

20 log

20 log

(f = 3000 Hz)

(f = 3000 Hz)

(dB)

s

(f = 3000 Hz)

(dB)

7200

− 2.64

8000

− 2.11

9600

− 1.44

14400

− 0.63

19200

− 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.

(1 − p1)P2

+

+

z − 1

p1

The difference equation for this correction filter is:

where the constant p1 determines the pole locations.

The resulting squared magnitude transfer function is:

p22 (1–p1)2

1 – 2p1 cos(2

p f fs) ) p12

|H(f)|2

+