| 摘要 |
1,225,738. Amplitude modulation; volume control. FERNSEH G.m.b.H. 18 June, 1969 [29 June, 1968], No. 30788/69. Headings H3R, H4R and H4T. [Also in Division G4] A circuit for multiplying two voltages comprises two field-effect transistors 1, 2 with their source-drain paths connected in series to form a voltage divider, the gate electrode of the first field-effect transistor 1 being connected to the common point of the transistors, which comprises the output terminal 4. The input for the first voltage comprises the terminal 3 of fieldeffect transistor 1 and may be fed in via capacitor 10 and D.C. restoring transistor clamp 11. The second input is fed over capacitor 6 to the gate of the second field-effect transistor 2, the D.C. operating point of which is determined by means of potentiometer 7 and resistors 8, 9. The impedance of the first field-effect transistor 1 may be adjusted by connecting a resistor between this transistor and the point 4, a D.C. bias being fed to transistor 1 via a first resistor and a further bias to the point 4 via a second resistor (Fig. 2, not shown). The arrangement may be used as a modulator, or for gain control; the Specification also refers to the compensation for varying sensitivity over the face of an image tube in television. |
