Patent GB-999231-A (GB)
Title: Improvements in or relating to parametric amplifiers
IPC: H04J3/20
Filed: 1963-01-09
Abstract: 999,231. Parametric amplifiers; automatic exchange systems. SIEMENS & HALSKE A.G. Jan. 9, 1963 [Jan. 10, 1962; July 19, 1962], No. 983/63. Headings H3B, H4K and H4R. In a parametric amplifier, switches S 1 , S 2  periodically apply a signal sample to a non- linear reactance when the reactance has one ] value and in a later phase of the pump frequency, when the pump has changed the reactance to increase the energy stored, they release the amplified sample to an output. The phases of the pump frequency Fp and the switch operating frequencies F 1 , F 2  are shown in Fig. 2. Low-pass filters serve as stores to smooth the input and the output. The switches S1 52 may be diodes with controllable discharge gaps or semi-conductor diodes. Both capacitive and inductive non-linear reactors are described. The direction of the amplifier may be reversed by changing the phase of the pump frequency by 180 degrees. The amplifiers may be used in a time division multiplex telephone exchange system. Circuits using capacitive reactance.-Backbiased semi-conductor diodes and capacitors using barium titanate as the dielectric are suitable reactors. As shown in Fig. 6, low-pass filters are used to smooth the input and the output. A bridge circuit enables the pump frequency to be applied to the capacitors without spilling into the signal circuit. Only a single switch is used in the arrangement shown in Fig. 7. The capacitor C p  is pumped with short pulses each of which commences before the switch S closes and terminates shortly after the charge transfer. A number of amplifiers using non-linear capacitors may be used in cascade (Fig. 4, not shown). In Fig. 10, a non-linear capacitor C 12  and a switch S are arranged in shunt between low inductors L 1 , L 2 . Inductive reactors.-Low-pass filters 1, 2, Fig. 8, including capacitors C l , C2 are linked by a non-linear inductor L 12  and a switch S. The inductor L 12  is controlled by a pumping winding (not shown) which is so arranged that there is no transformer coupling between the pump and signal circuits. Suitable circuits for coupling a pumping circuit to a signal circuit a, b are described (Figs. 13, 14, not shown). Inductor.-The main coil L 12 , Fig. 12, of a single inductor is wound on the central limb of a three-limbed core of ferrite split in two parts 3, 4. The core 3, 4 is included in the central limb of a further ferrite core split into two parts 5, 6. The control or pumping winding 7 embraces the central limb. Laminated transformer iron may be used in place of ferrite. Exchange system.-In a telephone exchange system using time division multiplex, substations TN, to TN n , Fig. 15, are linked to a common pulse highway ML by low-pass filters TP, parametric amplifiers L12 and gates S 1  to S n . When two gates S 1 , S n  are operated to interconnect substations TN i , TN ”  in a common time position, the amplifiers are pumped by pulses from a common source PG to amplify the signal pulses. Amplification is unidirectional and is restricted so as to avoid the regenerative effects of reflection while compensating for attenuation.