| 摘要 |
PURPOSE:To prevent the production of cross modulation due to harmonics caused by the nonlinearity of an input/output characteristic of an amplifier means by using a feedback circuit having the frequency selectivity transmitting the signal of an undesired band and not transmitting the signal of a band desired for amplification so as to apply a negative feedback to an amplifier means. CONSTITUTION:The output of an amplifier means AMP is fed back negatively to the input not through a pure resistance but through an impedance means Znfb having a frequency selectivity, the input impedance is a resistance Ri even to the signal of any frequency independently of the frequency. Since the negative feedback is applied not through a resistor but through the impedance means Znfb having a frequency selectivity, the gain to a signal at the outside of the desired band is decreased in selecting the frequency characteristic of the impedance means Znfb to have a high impedance with respect to a signal in the desired hand and to have a low impedance with respect to a signal at the outside of the desired band. Thus, it is prevented that harmonics at the outside of the desired band are inputted to the amplifier means and amplified.
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