Design And Implementation Of Large Dynamic Automatic Step-gain Control Circuit

Automatic gain control(AGC)is one of the basic circuits of wireless communication system.Its function is that when the large dynamic signal enters the receiver,the output power can be kept in a stable range through the automatic adjustment of the gain.On the basis of summarizing the research status at home and abroad,this paper introduces the theory of automatic gain control,the dynamic range and the establishment time of the loop.The detailed analysis of the variable gain amplifier,the detector and the gain control voltage generation circuit in the automatic gain control circuit are presented.According to the demand of the system gives an automatic gain control step realization method of 80 dB dynamic: using 30 dB,20d B,10 dB,20d B four stage low noise amplifier controlled by switching the mode will be required to gain access to the amplifier circuit,in order to realize the 10 d B step 0-80 dB dynamic range,and details the overall index distribution and plan.In this paper,the design of the proposed scheme is verified.According to the input signal of the 70 MHz,the low noise amplifier is used to amplify the power range which can be detected by AD8310,and the DC voltage of the detector is proportional to the decibel of the input signal voltage.The voltage is compared with the preset reference level of the comparator to generate a control signal for controlling the switching of the variable gain amplifier to achieve a change in the signal output level of the-20 dBm~0 dBm.At last,the design,processing,assembly,debugging and dynamic range test of the automatic gain control circuit module are completed.To achieve the sample measured results show that when the center frequency of 70 MHz signal changes in the range of from-10 dBm to-90 dBm,the output voltage detector changes linearly,ultimately the output power changes in the range of-14.83 dBm ~0 dBm,the noise figure is 5.385 dB,the maximum output power range linearly.The test results show that the basic requirements to meet the expected.Finally,the problems and solutions in the process of design and debugging are summarized.The circuit can also fully tap the potential,so that the output power range is smaller.The design has certain significance and application prospect in the dynamic range of the automatic gain control,the step by step realization mode and the stability of the system.