| 摘要 |
A telephone tone ringer chip, usable, inter alia, in the "chip set" of our Application No. 8317706 including tone generation circuitry (33-34), which can produce several different tone combinations under control of selection inputs (17, 18). The tone generation circuitry is powered by DC derived from a ringing signal on the telephone line via a diode bridge (32) and a DC-DC converter and anti-tinkle circuit (31). The chip includes an amplifier (30) which doubles as a speech amplifier when off-hook and when a loudspeaking facility is being used. When on-hook the amplifier (30) acts as a tone amplifier. To do this, its input stage includes two differential amplifiers, one for tone and one for speech, only one of which is enabled at any one time. The outputs from these two amplifiers go via a common amplifier to an output amplifier. The diode bridge is a complex arrangement in which each arm of the bridge includes a coupled pnp transistor and npn transistor which together act as a diode. <IMAGE> |
