| 摘要 |
1,181,124. Gain control in transistor amplifiers. RCA CORPORATION. 1 June, 1967 [13 June, 1966], No. 25458/67. Heading H3T. A forward-acting gain control voltage is applied from A.G.C. amplifier 52 to the gate of a field-effect transistor 10 acting as R.F. amplifier in a radio receiver. By-passed resistors 28, 36 are connected respectively in source and drain circuits and provide connection points for the emitter and collector respectively of an NPN transistor 48, the base of which is connected to the A.G.C. amplifier 52. Below a predetermined value of A.G.C. voltage transistor 48 is cut off, due to the reverse bias derived from the voltage drop across resistor 28: for greater values, however, the transistor is conductive and clamps the source to gate voltage of field-effect transistor 10. The gain beyond this point is reduced by the shunting effect of the emitter to collector path of transistor 48 on the D.C. supply to the field-effect transistor 10. |
