| 摘要 |
764,384. Automatic frequency control. HAZELTINE CORPORATION. Feb. 25, 1955 [March 31, 1954], No. 5731/55. Class 38 (4). [Also in Group XL (c)] In a circuit in which the emitter-base path of a transistor is biased in the forward direction and base-collector in reverse direction to provide a reactance, i.e. capacitance between the base 14 and collector 13, a control voltage 22 is applied in the base-emitter path to vary the magnitude of the capacitance which appears between the emitter and collector. The control voltage may be the unidirectional voltage of an automatic frequency control system. Alternatively, the control voltage may vary the mean operating frequency of an amplifier or control its pass band. The control voltage 22 varies the thickness of the layer at the junction 13, 14 and it is stated that if the magnitude of the variation is made small compared with the bias source 20 the modulation is linear. Inductors 21, 23 present a high impedance to R.F. from the generator 29, capacitor 40 by-passing these oscillations. The collector lead includes a lowfrequency inductor 33 shunted by a resistor 32, but the former may be omitted. Where a very high input impedance is required for the source 22, a grounded collector may be used, Fig. 3 (not shown). In a modification, Fig. 4 (not shown), the control voltage is applied to the emitter, the base being connected through inductor 21 to earth. |
