| 摘要 |
1317625 Variable reactance circuits, transistor amplifiers RCA CORPORATION 30 Sept 1970 [1 Oct 1969] 46438/70 Headings H3R and H3T A reactance, variable in response to a control signal comprises: a reactance 10; a circuit 20 for sensing the current through the reactance; and an amplifier 30, 40, having a gain dependent on the magnitude of the control signal 25, and being arranged to amplify the output current from the sensing circuit 20 and feed it back in parallel with the reactive element. The reactive element 10 may be the inductance of the resonant circuit 10, 12 of an oscillator which includes a positive feedback amplifier 14. A similar control circuit may be employed to vary the capacitive reactance, the two control signals being applied in push-pull, Fig. 4, (not shown). As shown, the output stage 40 of the current amplifier comprises a splitter, whose gain is varied by the control signal. In a modification, Fig. 5, (not shown), two splitters (40a, 40b), each controlled by push-pull control signals, are connected in cascade. Current amplifier and sensing circuit.-Variation in current at point 18 varies the current through resistor 228, the resulting change in potential across the resistor being fed back via transistor 234 to the base of transistor 224, thus varying the conductivity of transistor 224 to maintain the current through transistor 222 constant. The varying base potential of transistor 224 is also applied to the base of transistor 310 to produce a collector current I s which has a relationship to the magnitude of the collector current of transistor 224 in proportion to the relative base-emitter areas of the two transistors. As shown the collector current of 310 is one fourth that of 224 by virtue of the quadruple emitters of the latter. Transistors 310, 224, may be thermally coupled. In a modification, Fig. 3, (not shown), the circuit 20 is replaced by a single common emitter stage. |
