Solid State Ringing and Tone Equipment with Programmable Timing

The paper describes a new generation of electronic ringing and tone signal equipments. After presenting the block diagram the operation of the basic functional unite is described, such as the ringing generator - a voltage regulated transistor inverter -, tone generators with stabilized RC oscillators, tone contacts, timing circuits based on 1 PROM´s and digitized supervision circuits. High reliability is achieved using loadsharing principle for double sets. The structure based on functional modules gives versatility for different requirements on different markets and for applications to other than L M Ericsson exchanges. The Power Supply Department of L M Ericsson introduced a first generation of completely solid-state signalling equipment in 1968. The equipment has been installed in many countries and has shown satisfying function, good signal quality and no need of maintenance. The introduction of push-button telephones and new electronic exchanges has increased the requirements of both signal quality, (accuracy of levels, cross-talk, distortion) and reliability. The second generation of signaling equipment has been developed to meet these requirements. The objectives for the development work were: 1) The equipment should easily be adaptable to the varying specifications for signal frequencies, time patterns and signal levels required in different countries and for different exchanges. 2) The equipment should easily be extended when extending the exchange. 3) MTBF for a double set of signal equipment shall be more than 1000 years.