| 摘要 |
1,161,271. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 18 Jan., 1968 [25 Jan., 1967], No. 2699/68. Heading H4K. For multi-frequency signalling a common set of oscillators F 1 to F 6 is provided for a group of m registers, of which only Reg i is shown, the oscillators being coupled over transformers T 1 to T 6 to corresponding non-saturating long-tailed pairs of transistors Q 1 , Q<SP>1</SP> 1 to Q 6 , Q<SP>1</SP> 6 , in each register where the transistor pairs are commoned on the outlet to line LN. The transistor pairs are normally disconnected by contacts k 1 to k 6 selective operation of pairs of which connect frequency combinations to the line. Resistors R 9 to R 14 , or similarly placed constant current sources, maintain the output impedance of the pairs high. A Zener diode Z biases the transistor pairs to a level greater than the amplitude of the signals from the oscillators. |
