Automatic gain control (AGC) is used in a receiver to vary the gain in order to increase the dynamic range of the system. AGC also helps to deliver a constant amplitude signal to the detectors with different amplitude RF signal inputs to the receiver. AGC can be implemented in the RF section, the IF section, or in both the RF and IF portions of the receiver. Most often it is placed in the IF section of the receiver but placement is dependent on the portion of the receiver that limits the dynamic range. The detection of the signal level is usually carried out in the IF section before the analog/digital (A/D) converter or analog detection circuits. Often the detection occurs in the digital signal processing circuitry and is fed back to the analog gain control block. The phase lock loop (PLL) is analyzed and compared to the AGC analysis since both processes incorporate feedback techniques that can be evaluated using control system theory. The similarities and differences are discussed in the analysis. The PLL is characterized only for tracking conditions and not for capturing the frequency or when the PLL is unlocked.