SA5456 Ver la hoja de datos (PDF) - South African Micro Electronic Systems

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SA5456

PULSE/DTMF SWITCHABLE DIALLERS WITH 10 REPERTORY MEMORIES

South African Micro Electronic Systems 

SA545

8. Oscillator Circuit

This requires an external 560KHz ceramic resonator connected between OSC IN

and OSC OUT, providing a timing reference for all chip functions.

Consult your resonator supplier for recommendation of a suitable resonator type.

9. Tone Filtering

The spectral purity of the DTMF output is sufficient for most applications. However,

where lower distortion DTMF tones are required, an on-chip Darlington pair is

provided (accessible via pins 6 & 7) for use in a low pass active filter.

Figure 3 shows how a 2-pole Sallen and Key filter may be implemented. The typical

component values have been chosen to give a second order Butterworth response

with a cut-off frequency of about 3,5KHz and a nominal pass-band insertion loss of

0,5dB. The relative values of R3 and R4 may be adjusted to achieve the desired

DTMF amplitude which varies with supply voltage.

DTMF Tone Filtering

Figure 3: 2-Pole Sallen and Key Filter Circuit

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