| 摘要 |
912,755. Valve and transistor amplifying circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. Oct. 7, 1959 [Oct. 10, 1958], No. 34006/59. Class 40 (6). [Also in Group XXXIX] Signalling tone is passed over the cathode or emitter circuit of a valve or transistor amplifier to a line across which a variable number of load circuits may be connected in parallel, each load being connected in series with a resistor shunter by a capacitor such that a change in the number of load circuits produces a change in D.C. over the line which equals the resulting change in amplitude of the tone signal. As shown in Fig. 1, a tone source SB drives the base of a transistor T, the emitter circuit of which is loaded by subscribers' lines B1, B2 . . ., in series with resistors S and capacitors C in circuits coupled to the lines by transformers TR. Fig. 3 shows the static characteristics L11, L21, L31 ... of emitter current against the bias and signal potential V between ground and the transistor base. Provision of series resistors S shunted by capacitors C gives a set of dynamic characteristics L12, L22, L32 . . ., which have a common intersection G on the V-axis. By making the bias V1 exceed the co-ordinate value of G by the amplitude of the tone source the required relation between A.C. and D.C. in the emitter path is achieved. The load circuits are connected up by switches K which may comprise the diode arrangement of Fig. 4 where a flip-flop FF controls diodes G1 and G2. In this arrangement a rectifier G3 provides the voltage necessary between collector and base of transistor T. |
