We will introduce to you efficiency improvement techniques based on PA fragmentation techniques. Compared with other structures, the advantage of this principle lies in a very wide power range within which the power amplifier can be reconfigured. This range is determined by the level of granularity and complexity that the target application can afford. If the dynamic reconstruction is controlled by the envelope rate, for high PAPR applications such as WiFi, WiMAX, or LTE, this technology is expected to significantly improve efficiency. However, this technique may have two basic disadvantages. First, if the transmitted signal exhibits severe phase discontinuities, the receiver may have difficulty tracking the synchronization correctly, which can interrupt the radio link. Second, quantization noise causes false level regeneration. The error vector amplitude deteriorates and/or the test of the emission spectrum mask no longer passes. The following discussion will try to illustrate the ways in which these problems can be avoided, as long as some control/compensation circuits are integrated with the power core itself.
Introduction to the efficiency improvement of decentralized RF power amplifiers
Power amplifiers can be divided into power stages (Figure 1) and/or parallel topology (Figure 2) according to the cascade topology.
The reconstruction power range of dual cascaded/parallel distributed PA is shown in Figure 3. It is suitable for various operation modes.
When working, each power stage works in its best state, whether it is in Class E or Class AB. In the former case, efficiency is the priority, but envelope restoration is necessary. In addition, the corresponding POUT vs. PIN is roughly stepped, resulting in relatively high quantization noise; this is why the latter case is emphasized. In fact, the side effects (at the boundary of the reconfiguration range) are therefore reduced, and the result is that there is no too steep discontinuity in POUT vs. PIN.
Figure 1. Decentralized PA topology architecture based on cascade (bypass)
Figure 2. PA architecture based on parallel decentralized topology
Figure 3. Power range of decentralized PA processing
Based on DAS software, the system-level design method logic is divided into Four different parts, we will introduce these architectures one by one later.
In order to save design time, it is necessary to have a good understanding of the potential problems and trade-offs in this reconfigurable PA architecture. Figure 4 summarizes the cross-interaction relationship between the architecture parameters. The linearity requirement determines the basic architecture parameters, namely the oversampling rate and resolution. The higher these factors, the better the linearity. The dynamic power range of the reconstruction target also determines the performance and resolution M of the envelope detector used, as shown in the following equation:
Assuming that PAPR is a related evaluation of power ratio, the necessary result for WLAN applications is M=PAPR *ln(10)/10/ln(2)=4. In order to eliminate noise on the working bandwidth (that is, WiFi is 80MHz), the cut-off frequency of the baseband control system must be determined accordingly. The cut-off frequency of the power core reconstruction actuator must be set high enough to have a marginal impact on the overall architecture response time (WiFi>10*80M Hz). The linearity performance will be higher because the power gain deviation is minimal (in amplitude and phase) throughout the reconfiguration range. Output filter suppression near the operating bandwidth also positively affects linearity. On the contrary, the need for high efficiency forces the reduction of the in-band loss of the output filter (RESP, relative to current consumption), so that the achievable out-of-band suppression (RESP, relative to the achievable bandwidth of the analog circuit block) is limited. The output filter response is also determined using the duplex method. At first glance, for applications based on TDD rather than FDD duplex mode (for example, WCDMA), it is more recommended to use a decentralized power amplifier unless an output duplex filter with sufficiently high selectivity is used. From the perspective of TX efficiency, the development of BAW resonators is a promising enhancement technology because they have high-quality quality factors and can withstand high power densities, thereby dispersing the complexity of power amplifiers (resolution , OSR, reconstruction rate) relax a bit.
Figure 4. Design method description: problem / compromise
