In this thesis work, we implement an intermediate frequency (IF) amplifier circuit which processes IF signal to provide normalized baseband signal to the signal processing section at pulse radar systems. This circuit includes the low noise amplifier and the automatic gain control (AGC) network.
The AGC circuit reduces the amplitude fluctuation of received signal in radar systems while preserving useful informations of the modulated signal. A feedback circuit which consists of a variable gain amplifier, a detector and a filter is required for AGC.
The variable gain amplifier is implemented with a low noise amplifier (LNA) IC and two variable gain ICs. Using these circuits, we can obtain the maximum gain of 90dB. And the noise figure (NF) of 5dB is measured at 60dB gain. The detector is implemented in the form of differential amplifier using transistors to simplify the implementation. This detector converts the IF signal into a dc level.
As the received signal level varies, the input to the AGC circuit changes. The AGC loop detects the change and varies the gain of the IF amplifier in such a way that the output of the detector remains constant. To verify the operation of the proposed circuit, we measure the output characteristics of the AGC circuit with input signal dynamic range of 60dB. The output signal is very stable with only 2dB in amplitude fluctuation, preserving the useful informations of the modulated signal.
