| 摘要 |
PURPOSE:To provide the logarithmic amplifier which is equipped with a wide dynamic range and improves linearity. CONSTITUTION:An attenuator is inserted to one of two systems of an input signal, mutual signal levels are made different, and logarithmic transformation and A/D conversion is executed. A level switching point VL of both the signals is set by a reference voltage Vref. A switching signal 14 is outputted from an adder 7 near a saturation point based on the level switching point VL at a logarithmic amplifier (1)1 in a low level area. Corresponding to this signal 14, a hold circuit 8 holds the output signal of an A/ D converter (1)2, and the signal systems are switched to a logarithmic amplifier (2)5 by switchers (1)9 and (2)10. A synthesizer 11 synthesizes and outputs both the signals. The output signal is converted to an analog signal and outputted by a D/A converter 12. Since the signals at low and high levels are digitally synthetically joined, no synthetic distortion is generated. |
