| 摘要 |
PURPOSE:To simplify the constitution of the necessary muting function, by increasing enough the output voltage of the driver step forming a pulse modulating amplifier via the current switching logic circuit and at the same time securing the constant level for the output voltage to accelerate the rise and the fall. CONSTITUTION:Current switching logic (CML) circuits 10 and 11 are provided to produce the driving signals for output switching transistors (TR)Q3 and Q4 of the pulse duration modulating amplifier, and a pair of switching circuits comprising differential pairs TRQ5, Q6 plus Q7, Q8 are provided to circuits 10 and 11 each. Furthermore, constant current cources 5 and 6 are connected to the common emitter for TRQ5, Q6 plus Q7, Q8 each, and collector load resistances R4, R5 are connected to TRQ5, Q7 of one side. Then the fixed bias is applied to the bases of TRQ6, Q8 from the base bias circuit consisting of resistances R6, R7, R9, R8 each. And the current is supplied selectively to TRQ5, Q7 of one side in circuits 10 and 11 in accordance with the level of input signal B, and the current is supplied to TRQ6, Q8 via TRQ5, Q7. Thus the switching level is made constant for TRQ3, Q4 to ensure the assured control. |
