Digital Tone Generator
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
The modems are provided with an alarm device which sends a side band tone when there is a power failure. Such a device is generally an analog block with a capacitor tank loaded by DC voltage and providing the required energy for disconnecting the regular power supply from the oscillator, connecting the oscillator to the capacitor and sending the alarm tone over the line for 100 milliseconds (ms). Such an analog implementation has several drawbacks, mainly the noise generation caused by the harmonics of the tone because the oscillator is always running. The proposed approach is based on the fact that, after a power loss, the DC voltage remains within voltage specifications for at least 200 ms, and therefore can provide the energy needed to send the tone. In after a predetermined delay, e.g.