| 摘要 |
PURPOSE:To widen an input-output dynamic range by installing a circuit which shifts the DC level of an input signals to the input section of a differential amplifier and, at the same time, another circuit which logarithmically compresses the signal amplitude of a level shifted output to the input section. CONSTITUTION:An electric current I flowing to a transistor (TR) 62 is inverted and flows from a TR60 to another TR42. Simultaneously, the electric current I flowing to a TR66 is inverted and flows to another TR72. When the value of a resistance (R) 5 is set to the 1/2 of another R68, the electric currents 2I are absorbed at a TR52. When the voltage of a voltage source 55 is made equal to the voltage of the common terminal of the base and collector of the TR42, the electric current I flows to a TR44. An input signal supplied to the base of a TR70 is supplied to a level shifting circuit 48 and its DC level is shifted. The level shifted output of the circuit 48 is supplied to the base and collector of the TR42 and its amplitude is logarithmically compressed. In this case, a voltage drop corresponding to the AC component of the input signal is produced across both ends of an R77 and the voltage drop is fetched through a TR78 after the voltage drop is differentially amplified. Therefore, an input-output dynamic range can be widened. |
