| 摘要 |
PURPOSE:To operate a compression and expansion type noise reducing device even when a voltage is low, by using an inverting amplifier which has high efficiency of utilization of a power source. CONSTITUTION:When an input signal Vin is high, the base voltage of a transistor (TR) Q11 rises and the TRQ11 turns on. Then, a current flows from a power source line to TRs Q11 and Q14, a constant current circuit CS1 and an earth line. Since a voltage is applied to a TRQ13, its collector voltage approximates to a power voltage. A TRQ17 is supplied with the base voltage to turn on. Consequently the collector-emitter voltage of the TRQ17 drops. Namely, an output signal Vout becomes out of phase with the input signal Vin. An input and an output terminal are connected mutually through a negative feedback resistance Rf, so the base voltage of the TRQ11 is canceled by the Vout. Therefore, even when the power voltage is 2-3V, the Dolby system operates. |
