| 摘要 |
<p>1,012,709. Transistor amplifying circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. June 5, 1964 [June 8, 1963], No. 23409/64. Heading H3T. In a transistor amplifier with first and second stages, i.e. a radio receiver with R.F. and I.F. stages 11, 27 respectively, the amplified signal is detected, i.e. by diode 29 and used to provide a D.C. automatic gain control voltage to vary the gain of both stages inversely as the amplitude of the detected signal, the control voltage applied to the first stage being delayed, i.e. by diode 7 which is biased conductive from the supply line over resistor 9. According to the invention, D.C. conducting means are provided whereby the gain of the second stage increases as the gain of the first decreases; i.e., as shown, resistor 18 is provided in the collector circuit of transistor 11 and the potential at the collector is fed to the base of the second transistor 27 via resistor 17. For large signals the transistor 11 is cut off and acts as a capacity coupling and the gain of the second stage 27 then reduces as the detected signal level increases: the arrangement gives an improved signal to noise ratio and reduced cross-modulation.</p> |
