Meaning
Transient load currents drawn from the power supply of a wireless transceiver when the transmitter activates can cause voltage drops in the system. This power amplifier current pulse can exceed several hundred milliamperes for a fraction of a millisecond. If the power supply circuit cannot respond quickly enough, the voltage drop can reset the onboard microcontroller or disrupt sensitive analog stages.
Designers use decoupling capacitors and low-dropout regulators with high transient response to mitigate these surges.
Voltage Droop
The resistance of the battery and the impedance of the power tracks on the circuit board contribute to the voltage drop during a transmit event. When the power amplifier current pulse occurs, the voltage at the transceiver pins can drop below the minimum operating threshold. This droop is particularly severe when using lithium-ion or coin cell batteries.
Decoupling Strategy
Low equivalent series resistance capacitors placed close to the transceiver power pins act as local energy reservoirs. These capacitors supply the transient current during the start of the transmission, reducing the demand on the main power supply.
Layout Optimization
Wide power tracks and solid ground planes are used to minimize the inductance of the power delivery network. This layout reduces the impedance of the board, allowing for faster response to sudden load changes.
