Recently, a news about China Unicom shutting down 5G base stations from 21:00 to 9:00 the next day to reduce energy consumption and save electricity bills has attracted a lot of attention. Many people only know after seeing such reports that 5G base stations need to consume a lot of power.
At the beginning, everyone was generally concerned about the various benefits brought by 5G, such as higher speed, wider bandwidth, lower latency, and higher connection density, while ignoring the cost of such high performance. Now, with the acceleration of 5G construction and the gradual entry into the actual commercial stage, the landing challenges faced are gradually emerging. The 5G base station power supply is a road rover we encountered.
Why is 5G base station high power consumption?
To realize 5G mobile communication, it is first necessary to deploy a large number of 5G base stations, including macro base stations and small base stations (also called distributed base stations). The energy consumption of base stations is mainly electricity. The electricity bill for the base station computer room has also risen, so China Unicom needs to regularly switch on and off the 5G base station.
At present, the energy consumption of 5G base stations is mainly concentrated in four parts: base station, transmission, power supply and computer room air conditioner, and the electricity expenditure of base station accounts for more than 80% of the overall network energy consumption. In the energy consumption of the base station, the power consumption of the baseband unit (BBU) responsible for processing signal coding is relatively small, and the power consumption of the radio frequency unit (RRU/AAU) is relatively large.
According to the "5G Power White Paper" released by Huawei last year, although the power consumption per unit traffic has been greatly reduced from 4G to 5G, the total power consumption of 5G is still greatly increased compared to 4G. It is expected that in the 5G era, the maximum power consumption of 64T64R AAU will reach 1000~1400W, and the maximum power consumption of BBU will reach about 2000W.
In the 5G era, one site with multiple frequencies will be a typical configuration. It is predicted that the proportion of sites with more than 5 frequencies will increase from 3% in 2016 to 45% in 2023. One station with multiple frequencies will cause the maximum power consumption of the entire station to exceed 10kW, and the power consumption of sites with frequencies above 10 to exceed 20kW. In the multi-operator sharing scenario, the power consumption will double.
At present, the power consumption of 5G base stations has increased by more than 3 times compared with 4G base stations. In addition, due to the attenuation of coverage, the demand for 5G base stations has doubled. Therefore, for operators, the high power consumption of 5G base stations It has become the primary reason restricting the construction of 5G networks.
As the 5G network moves towards low/high frequency hybrid networking, in order to meet the business needs of increasing network capacity, a large number of peripheral sites will be deployed, the number of network sites will increase significantly, and the power consumption of the entire network will increase exponentially.
The impact of 5G on power design
Due to the increase in energy consumption of 5G base stations, electricity costs have become a factor that operators cannot ignore. Operators operating 5G base stations will pay more and more attention to the power consumption of base stations. Therefore, how to help operators save electricity bills has become an important topic. So to save electricity bills, the design of the power supply is an inescapable topic.
Cheng Wentao believes that the arrival of the 5G era has a very obvious impact on power supply design. He mainly talked about the impact of three aspects:
The first is that there will be more use of new materials, new topologies, and high-performance devices. "If you want to improve efficiency and save electricity bills, then the components used cannot be as strict as the 3G/4G era, and the cost requirements must be as strict as that in the 3G/4G era. You must use high-performance devices, good topology, and good materials." Cheng Wentao expressed in the live broadcast.
Second, the bus voltage will increase. Due to the increase in power consumption, the power supply design has also undergone some changes. For example, the communication bus that used 48V voltage before has to be upgraded to 72V, which will cause the output voltage of the switching power supply (DCDC) to change.
There are also reliability issues that are more of a concern. Since a very important feature of the base station is that after it is put into operation, it is basically unattended, so both equipment suppliers and operators have far higher requirements for maintainability, remote monitoring, and low failure rate. in other industries.
In fact, the power supply of the base station is mainly divided into three levels. Generally speaking, the power supply of the base station is 220V mains. The first stage is to convert 220V to -48V; the second stage is generally to use the module power supply to convert the -48V voltage to 48V or 28V for the PA power supply; the third stage is the board-level power supply, which is converted from 12V to each Voltage required for chips, analog circuits, digital circuits, etc.
Lupin believes that from the perspective of optimizing power supply design, three different levels of power supply have optimization work to be done. From the point of view of board-level power supply, there are three main changes:
One is that the current is increasing. In the 4G era, the single-rail current will not exceed 30A. In the 5G era, due to the use of many FPGAs, x86 chips, etc., the board-level current has greatly increased, reaching 50~60A. Therefore, the original power supply design cannot meet the design of these large currents.
Second, the number of channels has increased. As the signal chain becomes complex and sensitive, there are as many as dozens of channels of power rails on some single boards. This makes the complexity of the entire power supply design management much higher than before. The signal chain becomes complex and the sensitivity to noise increases accordingly. 5G power supply design engineers need to consider noise design and channel interference when designing.
Third, the ambient temperature has become higher. The biggest difference between the power supply of 5G communication and the power supply of the data center is that the power supply of the base station is outdoor. The variation range of ambient temperature is very wide, especially in the case of high temperature, the ambient temperature of the periphery may reach 60~70℃, and the internal temperature may exceed 100℃. In such a wide temperature range, the pressure is also very high for the power supply design.
How to deal with the challenges of 5G base station power design
For the macro base station, Cheng Wentao of Infineon gave some suggestions on the optimization of primary power supply and secondary power supply. "In the primary power supply, we see a clear trend is to require high efficiency and high power density. Now the efficiency of the power supply to reach 97%, or even 98% efficiency."
To achieve this efficiency goal, Cheng Wentao believes that first, a new topology needs to be used. For example, he said that the topology of ACDC will gradually transition from bridge PFC to bridgeless PFC, and even totem pole topology; second, it must adopt New materials, including the popular silicon carbide MOSFET and gallium nitride MOSFET; third, high frequency, which can improve power density and reduce size; fourth, chip packaging is more popular, and SMD packaging has become the mainstream.
For the secondary power supply, there are not many new topological structures, but more importantly, the use of new materials and high-frequency devices.
In terms of tertiary power supply, that is, board-level power supply, Lupin of MPS made a further explanation. In the 4G era, the design of high current is usually relatively simple, and a single-channel DCDC basically meets the needs. In the 5G era, after the current increases, more multi-phase power supply designs will be used. The reason is that after the multi-phase power supply design separates the controller and the power stage, it can be more efficient and bulkier than the traditional DCDC. advantages, and more flexibility.
Lupin pointed out that the direction of multi-phase power supply is developing in the direction of digitization, and digital power supply can provide many functions, such as monitoring of load status, monitoring of voltage and current, fault information, etc. There are many system-level optimizations, and the digital power supply can facilitate the management of the entire power supply, bringing great flexibility.”
The trend of high frequency of board-level power supply is also obvious, "many times, we will find that the area of inductor plus capacitor has exceeded the area of controller plus MOS tube, and if the frequency is higher, the passive device of the latter stage can do it. Smaller, so we are constantly advancing the development of high-frequency technology." Lupin further pointed out. He believes that the limiting factor of high frequency is not the controller, but the MOS tube technology. Therefore, MPS introduced the planar MOSFET technology. By using the planar technology, the Q level of the MOSFET can be made smaller. High frequency will bring great advantages, and now the highest frequency can reach 3MHz, which can greatly reduce the board area.
In addition to the multi-phase power supply, MPS also replaces the traditional DCDC plus LDO power supply mode with optimized power module technology in the analog power supply part. Lupin said that after their tests, the performance of the optimized module power supply is very close to the performance of the traditional DCDC plus LDO power supply mode.
He took a Zynq UltraScale+ RFSoC power supply reference design for Xilinx as an example, "We supply power to a 12-bit 2GSPS ADC and a 14-bit 6.4GSPS DAC on it, we directly use a switching power supply design, of course, it is not directly The DCDC, which is a power module, plus one-stage filtering, our ripple can be within 1mV, and the test results show that our solution can reach a level close to the power supply of the original LDO to the device.”
This is mainly closely related to the special technology adopted by MPS. Generally speaking, the core factor affecting EMI noise is the loop area, especially the loop area of changing current, which has a great impact on noise. The process can minimize the loop area from the chip to the inductor, including the input capacitor. In addition to the loop area, there is another factor that affects the stray impedance, or parasitic impedance. We use flip-chip technology and copper pillars. Replacing the original gold wire or copper wire can reduce the wiring impedance very effectively and also reduce the voltage spike. Therefore, through the combination of these two technologies, the loop can be reduced and the voltage spike can be reduced, which is very effective in improving EMI characteristics." Lupin said in the live broadcast.
In addition, the power module of MPS also adopts optimization measures such as symmetrical design, jitter of frequency duty cycle, and control of switching slope.
In terms of small base stations, in the 5G era, the radio frequency part and the antenna part will be more and more integrated, and this compact design also puts forward new requirements for power supply. For example, devices with higher withstand voltage levels are required, and SMD devices are used more and more; new material devices are more commonly used, including passive devices that use new materials for active devices.
In general, in the 5G era, how to reduce power consumption is a problem that the entire industry chain needs to think about. High efficiency, high power density, and high frequency will be the topics that the industry will continue to pay attention to. In Cheng Wentao's view, in terms of efficiency, for communication power supplies, when the efficiency of the power supply is improved to a certain level, the task of improving efficiency will fall on the radio frequency side, and the benefits of a little increase in the efficiency of the radio frequency side will be greater than the efficiency of the power supply part. Improvement; high power density can make the size of the device smaller, which will be the focus of continuous attention in the industry; high frequency needs to rely on new materials to achieve, including silicon carbide, gallium nitride, new magnetic materials, etc., because only active The high frequency of the device and passive device can be realized at the same time.
Therefore, for future 5G power supply engineers, they must be familiar with high-frequency design, familiar with new materials, and develop new ideas in order to adapt to future power supply design work.