| 摘要 |
1,219,623. Transistor switching circuits; keying oscillators. HITACHI Ltd. 7 June, 1968 [19 June, 1967], No. 27290/68. Headings H3R and H3T. [Also in Division G5] In a switching circuit such as for an electronic musical instrument, a rectifying element such as a diode 32 is connected between a signal input 21 and the base of a transistor amplifier 22, a switch 23 is connected to the emitter of the transistor so that the amplifier 22 is conductive when the switch 23 is closed and time delay means 24 sustains the amplifier 22 conductive for a predetermined time after the switch is opened and exponentially attenuates the amplitude of the output signal and the rectifying element 32 is forward biased when the switch 23 is closed and reverse biased when the switch 23 is open. As shown, the diode 32 is reverse biased and transistor 22 is OFF so that the signal from tone generator 21 which may be pulse or sine wave is blocked from the output 33. When the key switch 23 of an organ is closed the bias at points 34, 35 changes to forward bias the diode and turn ON the transistor 22 so that an output occurs at 33. When the key 23 is opened, switching OFF and reverse biasing of the diode is delayed by the charging of capacitor 29 through resistor 28 so that the output is reduced over a time delay. A plurality of PN junctions could replace the diode 32. Alternatively the base emitter junction of a transistor could be used in place of diode 32. In a modified circuit (Fig. 3, not shown), the signal source is connected between the diode and collector load supply which is earthed together with the terminal corresponding to +V 4 , the switch and capacitor 29 being connected to a negative supply (- V 5 ). When the diode 32 is blocked it prevents the signal being transferred to the output 33 which would be the case via the base-collector capacitance (14), Fig. 1 (not shown) as is known even although the transistor is biased off. |
