Overshoot Characterization

The primary metric defined as the ratio of the maximum amplitude peak to the final steady-state value, typically expressed as a percentage. In RF transmitters, this value is directly governed by the damping factor (ζ) of the power amplifier's bias control loop. An underdamped system (ζ < 1) produces a characteristic overshoot proportional to the phase margin of the feedback network.

• Calculation: (V_peak - V_steady) / V_steady × 100%
• Typical Range: 2-15% for commercial transmitters
• Hardware Origin: Gate bias network capacitance and parasitic inductance

The duration required for the transient amplitude to enter and remain within a specified error band (typically ±2% or ±5%) of the final steady-state value. This parameter reveals the dominant pole location of the PA control loop and the charging time constants of the bias decoupling capacitors.

• Error Bands: ±2% for precision measurement, ±5% for field analysis
• Hardware Correlation: PLL loop filter bandwidth and PA gate capacitance
• Fingerprinting Value: Highly stable over temperature for individual devices

The interval measured between 10% and 90% of the final steady-state amplitude on the leading edge. This metric captures the slew rate limitation of the power amplifier, which is a function of the bias current available to charge the gate capacitance and the impedance of the driver stage.

• Measurement Points: 10% and 90% of steady-state amplitude
• Dominant Factor: PA transistor transconductance (g_m) and load capacitance
• Statistical Property: Exhibits a Gaussian distribution across bursts from the same device

The resonant frequency of the ringing artifact superimposed on the overshoot peak, caused by the parasitic LC tank circuit formed by the PA's output matching network and the bias tee inductance. This frequency is a direct function of the specific reactive component values soldered onto the board.

• Origin: Parasitic inductance and capacitance in the output network
• Frequency Range: Typically 10-500 MHz depending on component values
• Discriminative Power: Highly unique due to component tolerance stacking

The concurrent phase excursion that accompanies amplitude overshoot, caused by the AM-PM conversion in the power amplifier. As the amplitude peaks, the non-linear input capacitance of the transistor shifts, causing a momentary phase deviation that traces a unique path in the complex plane.

• Measurement: Instantaneous phase deviation from steady-state phase
• Nonlinear Mechanism: Varactor-like behavior of transistor input capacitance
• Feature Extraction: Hilbert transform-derived instantaneous phase

The integrated power contained within the overshoot excursion above the steady-state level, computed as the squared magnitude of the analytic signal. This metric captures the total excess energy delivered to the antenna during the transient, which is proportional to the stored energy in the bias network's reactive elements.

• Calculation: Integral of (|analytic signal|² - V_steady²) over the overshoot duration
• Hardware Link: Energy stored in bias choke inductor and decoupling capacitors
• Robustness: Less sensitive to multipath channel distortion than shape-based features