GB744436A - Stabilized signal amplifier embodying semi-conductor devices - Google Patents

Abstract

744,436. Transistor amplifying circuits. RADIO CORPORATION OF AMERICA. Oct. 26, 1953 [Nov. 15, 1952], No. 29587/53. Class 40 (6). In an amplifier, two semi-conductor devices of opposite conductivity type fed in parallel are arranged so that means responsive to a difference in operating characteristics causes a change in the operating bias in a sense to reduce the difference. An amplifier, Fig. 1, of the type described in Specification 736,063 feeds a load Z, the input being applied in parallel to complementary transistors 10, 11 to produce additive A.C. collector currents in the load. The base resistors 24, 25 are returned to a point A on the load Z having a resistive component to earth. In the absence of a signal, any variation of characteristic tending to make point B positive will raise the potential of point A, and hence that of the base electrodes of the transistors. The collector current of transistor 10 will therefore be reduced and that of transistor 11 increased so that point B is brought nearer earth potential. In a modification, Fig. 2, the circuit operates in class B, transistors 30, 10 and 31, 11 conducting on successive halfcycles. The load Z may' be a loud-speaker voice coil or the deflection coils of a C.R.T., Fig. 3 (not shown), and may take other forms to give the amplifier various characteristics. The selected load is arranged to have a suitable resistive component to earth. With the components of Fig. 5, feedback voltage is proportional to output current or the first derivative of the current if the circuit of Fig. 6 is employed. The circuit of Fig. 7 provides feedback only at the resonant frequency of the tuned circuit 50, 51 so the amplifier rejects this frequency. With the resistor 49 and tuned circuit 50, 51 interchanged, Fig. 8 (not shown), the amplifier is selective and gives high gain only at this frequency.