| 摘要 |
A circuit for the bidirectional transmission of voice and signalling, e.g. as an interface between a PABX and a public exchange, uses electrical isolation by an opto-coupler (OK), and DC line looping effected by pulse duration modulation by a comparator (K2). Band width range is from DC to about half pulse frequency. The pulse generator is a self- oscillating circuit including a comparator (K1) and an integrator (OP4). The pulse duration modulated signal is controlled in amplitude from the incoming signal via a differential amplifier (OP1). <IMAGE> |
