| 摘要 |
PURPOSE:To achieve an AGC control suitable for monitor, by inserting a nonlinear DC amplifier corresponding to the change in the sensitivity of a PIN diode which is inserted to an AGC amplifier to compensate the fluctuation of a reception input electric field and to obtain a constant output to an AGC loop. CONSTITUTION:An input signal at a point A is amplified 1, attenuated at the resistance compoenent of a PIN diode D3 and amplified 5 and outputted from a point B. A control voltage applied at a point C is applied to the D3 via resistors R2, R4 to determine the attenuation to signals. The output at the point B is detected 6 to drive an AGC control circuit consisting of an error amplifier 7 and an operational amplifier 11. The amplifier 7 is connected to an inverting input of the operational amplifier 11 via a D8 equivalent to the D3 and the noninverting input is grounded. The negative feedback circuit of the amplifier 11 is formed with a series circuit consisting of a D9 equivalent to the D3 and an R10 equal to the sum of the resistors R2, R4. Thus, the fluctuation of the AGC loop due to change in the D3 can be compensated. A linear AGC voltage to the logarithm of input is obtained. |
