Technical Articles/White Papers

Cellular communications have come a long way since the introduction of analog cellular networks in the early ’80s. Today, as the market migrates from 4G to 5G network solutions, the cellular communications industry is laying the groundwork for a giant leap forward in data transfer speed, lower latency, capacity, user density, and reliability. For example, along with a 100× improvement in data rates and network capacity (10×), 5G also drastically cuts latency to under 1 ms,1 while enabling near ubiquitous connectivity for the billions of connected devices that are part of the growing Internet of Things (IoT). A typical 5G beamforming transmitter comprising digital MIMO, data converters, signal processing components, amplifiers, and antennas is shown in Figure 1.2

Powering FPGAs
In order to fully realize the benefits of 5G, designers require higher frequency radios to tap into the new spectrum needed to meet the future data capacity demand by incorporating more integrated microwave/millimeter wave transceivers, field programmable gate arrays (FPGAs), faster data converters, and high power, low noise power amplifiers (PAs) for smaller cells. Additionally, these 5G cells will also include more integrated antennas to apply the massive multiple input, multiple output (MIMO) techniques for reliable connections. As a result, a variety of state-of-the-art power supplies are required to power 5G base station components.
Modern FPGAs and processors are built using advanced nanometer processes because they often perform calculations at fast speeds using low voltages (<0.9 V) at high current from compact packages. Additionally, new generation FPGAs need lower core voltages to vastly improve computational speeds while requiring higher voltage for I/O interfaces, and they need an additional rail for DDR memory.3,4,5 So, in essence, a single FPGA requires multiple voltages with tight tolerances and different current ratings for optimal operation. What’s more, in order to avoid damage, these voltage rails must be sequenced in the correct order. Such stringent requirements can be met by power supplies built using the latest semiconductor technologies combined with leading-edge circuit topologies and advanced packaging techniques. However, should a designer not properly utilize the right power management solution, the risks range from inefficiencies to thermal complications and other undesired performance-related problems.

Quietly Powering High Speed Data Converters
Likewise, faster running, precision data converters, like analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), also require multiple power rails, such as 1.3 V, 2.5 V, and 3.3 V, with very low noise and dc ripple.6 Normally, these high speed ADCs and DACs are placed on crowded printed circuit boards (PCBs) with limited space. Consequently, power supply sensitivity of the ADC and DAC must be a top consideration when designing the power supply system for these high speed data converters.

Figure 1. A high level block diagram of a beamforming transmitter for 5G systems.

By combining the benefits of advanced semiconductor and packaging technologies, ADI’s µModule® Silent Switcher® regulators can easily solve this problem, meeting the efficiency, density, and noise performance needs of high speed data converters. A good example is Silent Switcher LTM8065, which can deliver a solution that is quiet, more compact, and more efficient for powering these devices. Unlike a traditional discrete solution, LTM8065 can significantly cut the component count and power supply board real estate without compromising the dynamic performance of the data converter. A single RoHS compliant BGA package integrates a switching controller, power switches, an inductor, and all the supporting components.
In some cases, to maximize power supply rejection ratio (PSRR) performance, linear regulators are used in the power supply path, following a switching regulator. ADP7118 is one such low dropout (LDO), low noise linear regulator that can handle a wide input voltage range with high output accuracy, low noise plus high PSRR, and an excellent line and load transient response. However, there are many more in this product line and they can be correctly selected using ADI’s software tools like LTpowerCAD and LTspice.®

Managing Power for PAs and Transceivers
These next-generation radios that incorporate integrated transceivers and low noise, high power microwave/millimeter wave PAs with wider bandwidths come with digital control and management systems, which requires the use of multiple specialized power-supply technologies. For example, gallium nitride (GaN)-based low noise, high power PAs will require voltages as high as 28 V to 50 V, while FPGA based control and high speed ADCs and DACs will need multiple lower voltages with proper sequencing, monitoring, and protection.7,8 State-of-the-art dc-to-dc converters can deliver the efficiency (>90%), power density, low noise performance, and control demanded by these 5G PAs.

With enormous pressure to deliver next-generation (5G) products that outperform the previous generation (4G), there is little room for compromise. Consequently, a company like ADI, which specializes in all aspects of the base station RF chain and has thorough knowledge of power management tools required for powering these applications, is able to provide the right power resources for today’s 5G based PAs and transceivers. Offering the industry’s broadest portfolio of high performance Power by Linear™ products ranging from high efficiency, high density dc-to-dc converter modules to power management ICs (PMICs) and ultralow noise linear regulators, including power sequencing, monitoring, and protection, ADI can provide a more holistic approach to powering the 5G signal chain.

ADI’s µModule regulators and Silent Switcher services are complete power system-in-package solutions that can deliver precise voltage with the highest efficiency (>95%) and power density from a miniature package with high reliability and the lowest EMI and noise. These solutions are specially designed to power high performance RF systems with the highest power conversion efficiency and density without adding noise or interference to the radio signal of interest, thus ensuring the best performance out of these RF PAs and other such RF circuits.

Likewise, to address the challenges of power supply sequencing in circuits where multiple rails are needed, ADI has built a family of sequencers ranging from sequencing of two supplies (ADM6819/ADM6820) to 17 channels (ADM1266). To ensure that a system is operating correctly, efficiently, and safely, monitoring device voltage, current, or temperature is crucial. For that, ADI offers parts like LTC2990.

In summary, ADI’s Power by Linear product portfolio comprises low noise LDO regulators, low EMI, highly integrated multirail dc-to-dc converter µModule devices, Silent Switcher technology, and other power management ICs, including supply sequencers, monitors, and protection circuits – all of which position ADI to offer the broadest line of power products in the industry. It includes everything needed to power 5G base station components, including software design and simulation tools like LTpowerCAD and LTspice. These tools simplify the task of selecting the right power management solutions for these devices and, thereby, provide an optimal power solution for 5G base stations components.

By James Wong and Tony Armstrong, Analog Devices Inc.

References
1 Kyungmin Park. “How 5G Reduces Data Transmission Latency.” EDN Network, May 14, 2018.
2 Thomas Cameron. “5G—The Microwave Perspective.” Analog Devices, Inc., December 2015.
3 Nathan Enger. “Care and Feeding of FPGA Power Supplies: A How And Why Guide To Success.” Analog Dialogue, November 2018.
4 Frederik Dostal. “Power Management for FPGAs.” Analog Dialogue, March 2018.
5 Afshin Odabaee. “Powering Altera Arria 10 FPGA and Arria 10 SoC: Tested and Verified Power Management Solutions.” Analog Devices, Inc.
6 Aldrick Limjoco, Patrick Pasaquian, and Jefferson Eco. “Silent Switcher µModule Regulators Quietly Power GSPS Sampling ADC in Half the Space.” Analog Devices, Inc., October 2018.
7 David Bennett and Richard DiAngelo. “Power Supply Management of GaN MMIC Power Amplifiers for Pulsed Radar.” Analog Devices, Inc., October 2017.
8 Keith Benson. “GaN Breaks Barriers—RF Power Amplifiers Go Wide and High.” Analog Dialogue, September 2017

Underwriters Laboratories (UL), the author of the U.S. and Canada smoke detection standards, has released a revised specification (8th edition). These new standards are significantly more technically challenging to meet than the current regulations.

New Smoke Detector Tests
One major change to the standards is the introduction of the hamburger nuisance test. In this test, hamburgers are placed in an oven set at a high enough level to eventually burn, and the detectors must not issue an alarm before a certain amount of smoke has been generated. This requirement to not alarm will bound the maximum sensitivity of a detection system. This test is designed to reduce the number of false alarms generated due to cooking events, as residents disconnecting alarms due to high false alarm rates is one of the leading cases of death in fire-related events.

Another addition to the standard is the flaming polyurethane (PU) test, also known as the burning couch cushion test. Due to the optical scattering cross-sections and physics of different smoke types, sensor response from flaming PU is lower than the response from other smokes at a similar obscuration. As such, the ability to detect flaming PU smoke at specified levels will bound the minimum sensitivity of most, if not all, optical detection systems. In practice, the sensor response to the flaming polyurethane smoke can be difficult to separate from the hamburger nuisance test. In the past, setting the pass/fail criteria for a detector was straightforward, at least to minimally meet agency requirements. For the upcoming requirements, the manufacturing and calibration margins are much tighter and may require an increase in algorithmic complexity. The flaming polyurethane and hamburger nuisance tests occur on different time scales and it is straightforward to create a simple algorithm that looks at the slope or rate of change of the smoke to distinguish between the two fires to pass the UL requirements. However, there is a question of how effective this algorithm is in real-world applications.
In fire room tests, the pass criteria are specified in either time passed since the test was initiated or at a defined obscuration level. A typical obscuration sensor is shown in Figure 1, with a light on one end and the photodetector on the other end. For UL tests, the beam is a sodium vapor lamp 4″ diameter and 5′ long. Particles in the path of the beam absorb or scatter light out of the beam path, reducing the amount of light that reaches the detector. For different types of smoke, the relationships between an optical scattering system and an obscuration are different. In the case of the hamburger nuisance test and flaming polyurethane test, a 3× difference in obscuration can be nearly impossible to differentiate in an optical scattering system.

A Typical Smoke Detector
A typical smoke detector is made up of a detector, a microcontroller with an algorithm, and additional components such as loudspeakers, LED indicators, and CO sensors. Photoelectric smoke alarms often use a discrete LED (typically near-infrared, 850 nm or 880 nm) and a discrete photodiode with a typical 135° angle between them and a separation of several cm.

Figure 1. Reference measurement.
LED light of a specific wavelength is scattered by particles onto a photodiode. As shown in Figure 2, the distance between the LED and the photodiode is usually a few centimeters.

Figure 2. Forward scatter system with an infrared LED.
However, both the discrete design of the smoke alarm and the measurement method result in a few disadvantages. The main one is that monochromatic LEDs lead to a higher false alarm rate because they make it harder for different particles to be distinguished from one another. In addition, a discrete implementation is large and associated with a higher power consumption. Laborious calibrations are also necessary. The technology for the optical components has advanced to the point that the LEDs and the photodiodes, along with the optical front end, can be integrated into a small housing.

Addressing the New Challenge
ADI has created a technology to help address these issues: the ADPD188BI. It directly integrates two LEDs (blue and infrared), a photodiode, and an analog front end. Digital output over I²C or SPI enables a connection to a microcontroller. A block diagram of the ADPD188BI is shown in Figure 3. As can be seen in the figure, the complete signal chain is realized in a single 5 mm × 3.8 mm chip.

Figure 3. Block diagram of the ADPD188BI.
The ADPD188BI works by emitting a short LED pulse of a few microseconds. Some of this light is scattered by the smoke particles back onto the photodiodes (see the cross-section of the ADPD188BI in Figure 4). The analog front end (AFE) includes the transimpedance amplifier, band-pass filter, integrator, ADC, LED drivers, and digital control (see the middle of Figure 3). There are many options inside the AFE to enable optimization for different applications and use cases. The AFE also provides the ability to reject ambient light, such as from lamps or solar radiation at levels up to 80 dB.

Figure 4. Cross-section of the ADPD188BI.
This principle provides many significant advantages. The short distance between the LED and PD results in much more efficient use of light, which reduces the power dissipation of the system for a required sensitivity and results in a longer battery lifetime. Two different LED colors are included in the device. The amount of light scattered by the particles is a function of wavelength. This provides limited use for separating the hamburger and flaming polyurethane smokes, but can be used to distinguish between relatively small smoke particles (100 nm to 300 nm diameter) and much larger smoldering plastic or steam particles (10 μm diameter). The highly configurable AFE inside the ADPD188BI provides for a very high dynamic range that is software configurable and can be adjusted on the fly. The SNR of the system can also be easily adjusted to optimize for power or performance on the fly. One example would be to dynamically increase the sample rate or SNR when smoke has been detected to more accurately differentiate between a nuisance source or a real fire. The integration of the system also enables Analog Devices to calibrate the loop response (LED driver  LED  PD  AFE) of the parts and burn calibration coefficients into the AFE to limit the part-to-part variation to better than ±10%, which reduces or eliminates the need for expensive and time-consuming sensitivity calibrations in smoke tunnels. The ADPD188BI provides the features and capabilities to increase the performance of smoke detectors to more accurately separate nuisance sources from fire events. As well as performance, there are further advantages: the integration of LEDs means separate LED sourcing and stocking is eliminated, and the small form factor allows for integrated smoke detection across intelligent building components.
About the Author
Christoph Kämmerer has worked at Analog Devices in Germany since February 2015. He graduated in 2014 from the Friedrich Alexander University in Erlangen with a master’s in physics. He then worked as an intern in process development at Analog Devices in Limerick. Having completed the trainee program in December 2016, he now works as a field applications engineer at Analog Devices and specializes in emerging applications. He can be reached at christoph.kaemmerer@analog.com.