75T204-IL 데이터 시트보기 (PDF) - TDK Corporation

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75T204-IL

5V Low-Power Subscriber DTMF Receiver

TDK Corporation 

75T204

5V Low-Power Subscriber

DTMF Receiver

APPLICATION INFORMATION

The 75T204 will tolerate total input RMS noise up to

12dB below the lowest amplitude tone. For most

telephone applications, the combination of the high

frequency attenuation of the telephone line and

internal band-limiting make special circuitry at the

input to the 75T204 unnecessary. However, noise

near the 56kHz internal sampling frequency will be

aliased (folded back) into the audio spectrum, so if

excessive noise is present above 28kHz, the simple

RC filter shown in Figure 5 may be employed to

band limit the incoming signal.

Noise will also be reduced by placing a grounded

trace around the XIN and XOUT pins on the circuit

board layout when using a crystal. It is important to

note that XOUT is not intended to drive an additional

device. XIN may be driven externally; in this case

leave XOUT floating.

NOISY

SIGNAL

2.4 k = 5%

ANALOG IN

75T204

0.01 mF = 20%

FIGURE 5: RC Filter

6

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