| 摘要 |
<p>PURPOSE:To make a subscriber circuit main body into an LSI at low cost by a PN junction separating process, by supplying a substrate voltage after performing the double voltage commutation of the output of a call sound source, and suppressing a signal voltage supplied from the call sound source to the subscriber circuit main body so as not to exceed the substrate voltage by a protection circuit. CONSTITUTION:A double voltage commutation circuit E connected to a call sound source B is constituted of two diodes D1 and D2, and two capacitors C1 and C2, and performs the double voltage commutation of the signal voltage outputted from the call sound source B, then generates a DC voltage of (2xVRING;-180V) as a substrate voltage VSUB for a subscriber circuit main body A. Also, a diode D3 as a protection circuit F is connected between the substrate voltage input terminal of the subscriber circuit main body A, and a terminal to which the signal from the call sound source is inputted. When the signal voltage from the call sound source becomes excessive transiently by the diode D3, it is clamped by the substrate voltage VSUB. Therefore, an inter-element separation between transistor cells in the subscriber circuit main body A that is made into the LSI by the PN junction separating system is secured by the substrate voltage, and its operation can be stabilized.</p> |
