| 摘要 |
PURPOSE:To obtain a high-quality picture with proper contrast even at a high/ low part of a signal level by converting a sample information signal with a large dynamic range into a signal with small amplitude and forming the picture. CONSTITUTION:The logarithmic amplifier 19 consisting of plural cascaded intermediate frequency amplifiers and an amplitude limiting and summing detector which sums up the outputs of those intermediate frequency amplifiers over amplitude limitation and performs detection is interposed between a mixer part 12 and a signal processing circuit 20. An intermediate frequency signal from the mixer part 12 is led to the logarithmic amplifier 19. The logarithmic amplifier 19 is equipped with intermediate frequency amplifiers 21, 22, and 23 to amplify an intermediate frequency signal whose intermediate frequency ¦f1-f2¦ is, for example, about 60MHz by about 20dB, and they are cascaded to lead the outputs of the amplifiers 21, 22, and 23 to specific input terminals (a), (b), and (c) of the amplitude limiting and summing detector 24; amplitude limitation and summing detection are performed and the resulting detection output signal is led out through a buffer amplifier 25. |
