Image Number 4 for United States Patent #6903611.
An automatic gain control device without being influenced by leakage current of a capacitor. The automatic gain control device includes a first control loop, a second control loop, and a multiplexer. The first control loop receives an input voltage and generates a first control voltage. The second control loop receives the first control voltage, digitizes the first control voltage, and outputs a second control voltage by a DAC. The multiplexer chooses the first control voltage or the second control voltage as a gain control voltage according to a hold signal. Because the second control loop digitizes and holds the first control voltage and output the second control voltage from the DAC, the gain control voltage can be held constant for a long time without being influenced by leakage current.