But this motivation is provided by the Wireless Communications Standards Committee, which uses signal modulation to increase the peak power ratio of the signal. If the signal PAPR is just 3dB or less, adding DPS may not do much good. When the signal PAPR exceeds 5 dB, the advantage of combining DPS into the transmitter to improve its energy efficiency will increase rapidly.
Envelope tracking (ET,Envelope tracking) is a DPS technology that aims to improve the energy efficiency of a linear power amplifier (PA,power amplifier) by matching the voltage at both ends of the RF power transistor with the lowest actual voltage required to accurately provide the current instantaneous output power. Therefore, the PA power supply follows the envelope of the output signal and has a moderate correlation-hence the name: envelope tracking (envelope tracking)-while keeping the linear operation of the power transistor nominally unchanged. The core principle is based on ensuring that no matter what the voltage is applied at the PA, it is not critical to the accuracy of the output signal modulation. Therefore, Envelope tracking (ET,Envelope tracking) is one of many technologies used for a century to build linear power amplifiers and make them energy efficient at the same time.
It is recognized that improving the efficiency of amplifiers operating below their maximum output signal power by reducing applied power supplies and bias voltages is included in an important publication of 1989 [B. Geller, P. Assai, B. Gupta, and P. Kline, "A Technique for the Maintenance of FET Power Amplifier Efficiency Under Backoff," Digest of the 1989 IEEE Microwave Theory and Techniques Symposium, pp. 949Mel 952.]. This does not attempt to follow the signal envelope, but only the signal power, a technique now known as average power tracking (APT,average power tracking). The power amplifier uses the input signal envelope to control the step change of the power supply voltage, which was first released in 1995 [C. Buoli, A. Abbiatti, and D. Riccardi, "Microwave Power Amplifier with 'Envelope Controlled' Drain Power Supply," Proceedings of the 25th European Microwave Conference, Sept. 1995, pp. 31 Mel 35. The design uses a lower supply voltage to switch the supply voltage applied to the RF power transistor between two values, but applies a higher voltage when the input signal has a large peak. Now, more than 20 years later, this technology of temporarily switching power supplies to support high peak output power is called Class G [J. S. Walling, S. Taylor, and D. J. Allstot, "A class G Supply Modulator and Class E PA in 130nm CMOS," IEEE Journal of Solid-State Circuits, vol. 44, no. 9, Sept. 2009.] .
Use a variable power supply (dotted curve) to reduce RF PA power consumption, which remains high enough above the peak value of the RF waveform to ensure that the RF power amplifier operates linearly at all output power.
The first known ET discussion, in which the applied power supply varies continuously with the input signal envelope to reduce power consumption in the transistor, is published in 1999 [G. Hanington, P. Chen, P. Asbeck, and L. E. Larson, "High Efficiency Power Amplifier Using Dynamic Power-Supply Voltage for CDMA Applications," IEEE Transactions on Microwave Theory and Techniques, vol. 47, no. 8, Aug. 1999 pp. 1471 1476.]. In this article, DPS is a DC-DC boost converter operating at a switching frequency of 10 MHz. The ripple of the output of this power supply will be coupled to the output signal as an unwanted sideband, in order to ensure the linearity of the RF amplifier to maintain its suppression of the power supply noise, so this problem has received special attention. The purpose of ET is to implement the operations shown in. From the mobile device's point of view (using the battery as the power supply voltage), the goal is to keep the voltage drop on the RF transistor as low as possible. The current through the RF transistor depends largely on the necessary output power, so the transistor current cannot be changed. Therefore, reducing the supply voltage does reduce the power consumption of the RF transistor.
While reducing power dissipation in RF power transistors is useful, reducing the current drawn from primary voltage sources is often equally important to take advantage of the improved energy efficiency of RF power transistors.