Patent ID: 7269398

Claim:
An automatic gain control circuit for a receive apparatus for a mobile object which automatically controls the gain of a variable gain amplifier amplifying a received signal from an antenna installed in the mobile object and outputting the amplified signal to the receive apparatus, the circuit comprising: an intensity detector that detects an intensity of the received signal; a comparator that compares the detected intensity with first and second threshold voltages; and a controller that outputs a control signal for adjusting the gain to the variable gain amplifier based on the comparing results of the comparator so that the gain of the variable gain amplifier has a hysteresis with respect to the intensity of the received signal, wherein the second threshold voltage is greater than the first threshold voltage; a gain G 1 and a gain G 2 greater than the gain G 1 are made to correspond to the first threshold voltage; and a gain G 3 and a gain G 4 greater than the gain G 3 are made to correspond to the second threshold voltage, and wherein the controller, based on the comparing results of the comparator, outputs the control signal to the variable gain amplifier to increase the gain from the gain G 2 to the gain G 4 when the intensity of the received signal detected by the intensity detector increases from being smaller than the first threshold voltage towards the second threshold voltage, and to decrease the gain from the gain G 3 to the gain G 1 when the intensity of the received signal detected by the intensity detector decreases from being greater than the second threshold voltage towards the first threshold voltage.