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Design Notes

AGC using RF_PID

(Automatic Gain Control using Proportional Integral Derivative Controller)

VSS can be used to analyze linear and nonlinear effects in a typical AGC application.  A common requirement of RF systems is a reduction in signal power variation at the input of the data converter to prevent saturation.  In this example LVGA is used as the variable gain element to control the output power of the RF link.  The signal power at the output of the RF link is monitored by the RF_PID block, which generates the control signal to the LVGA based on the measured and target power levels.

Details

The system diagram RF_PID Feedback performs a power sweep of the AGC line-up.  The plots that are generated from this schematic are shown in the Graphs titled Power Gain vs Input Power, Output Power vs Input Power and OIP3 vs Input Power, and Output Power vs Component @ -30dBm Pin.

Tuning the Target AGC Power Level  variable Pout  shows the effect on the AGC range.  Observe the graph Output Power vs Input Power.

Tuning the Gains G1 , G3 and G4  shows the effect AGC effect on gain distribution through the chain. Observe graph Output Power vs Component @ -30 dBm.

Its also possible to see the effect on OIP3 in the graph OIP3.

System Diagram - RF_PID Feedback

Graph - Output Power vs Component

Graph - Power Gain vs Input Power

Graph - OIP3

Graph - Output Power vs Input Power

Graph - Control Signal