Question

In DTMF, the circuit operates over the supply voltage range from

• A. 3 volts to 25 volts
• B. 3 volts to 15 volts
• C. 3 volts to 20 volts
• D. 3 volts to 30 volts

Hint:

Because DTMF generator ICs use low-power CMOS technology, they can run directly on the small current supplied by the telephone line, eliminating the need for an external power outlet or battery in landline telephones.

Answer 1

The Correct Option is B

Step 1: Understanding DTMF Technology:
DTMF (Dual-Tone Multi-Frequency) is the dialing system used in modern push-button telephones. When a key is pressed, it generates a unique combination of two audio frequencies (one from a low group and one from a high group).

Step 2: Identifying the Operating Voltage of DTMF ICs:
Modern push-button telephones are powered directly by the low DC voltage on the telephone line. The DTMF generator integrated circuits (such as the standard UM91214 or MT8870 series) are designed as low-power CMOS devices. To operate reliably on varying line voltages, these ICs are designed with a wide operating supply voltage range, typically from 3 volts to 15 volts.

Step 3: Conclusion:
Therefore, the standard operating voltage range is 3 V to 15 V, corresponding to option (B).