| 摘要 |
A circuit for converting a log signal to a linear signal wherein automatic gain control is performed before the signal is linearized. The circuit includes a bipolar transistor connected to use its diode characteristic for converting a log signal to a linear signal, and a fixed gain linear amplifier to provide the necessary gain/bandwidth product reguired for the circuit. The circuit additionally includes a peak detection circuit that detects the peak voltage output from the linear amplifier and supplies this voltage to an integrator. The circuit determines the peak voltage of the output signal and generates an error voltage when the peak voltage exceeds a reference voltage. The error voltage is summed into the base of the transistor that performs the logarithmic-to-linear conversion function. The need for a variable gain stage in the linear amplifier is eliminated. In addition, the circuit eliminates the DC component of the input signal and produces a linear AC output signal that is controlled to a predetermined maximum amplitude. The antilog circuit is preferably connected to the output of a log amplifier and provides an AC output signal that is linear function of the modulation on the input to the log amplifier.
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