Technology Sharing

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The idea of ​​vehicles sharing information and working together to make transportation safer, greener, and more enjoyable is very appealing. The various technologies associated with this concept, collectively known as cooperative intelligent transportation systems (C-ITS), are expected to ease traffic congestion, reduce the environmental impact of transportation, and significantly reduce the number of fatal traffic accidents.

In this chapter, I will discuss the connected car and vehicle data, opportunities and use cases, and RF semiconductors in the connected car.

Connected Cars and Data

Cars are transforming from standalone objects used primarily for transportation to advanced Internet-connected endpoints, often capable of two-way communication. The new data streams generated by modern connected cars drive innovative business models such as mileage-based insurance, enable new in-car experiences, and lay the foundation for advances in automotive technologies such as autonomous driving and V2V communication.

There are two main approaches to the connected autonomous vehicles of the future. One technology is based on the IEEE 802.11p standard, and the other leverages C-V2X over cellular infrastructure. How the two approaches will blend and connect to each other. Ultimately, they will both connect to the LTE/5G infrastructure network, but in different ways.

With the introduction of various communications, the number of electronic communication systems inside cars has increased significantly. As shown in Figure 3-4, there are multiple RF front-end (RFFE) chains and antennas inside the car, such as Wi-Fi, cellular, Bluetooth, etc. In addition, some standards marked in Figure 3-4 have more than one or two signal paths.

Many of these RF chains contribute to new automotive system intelligence.

First, the system intelligently collects data from sensors, cameras, and in-vehicle connectivity to provide important data and services. RF components such as amplifiers, switches, filters, and highly integrated modules add important functionality to automotive processing and communication systems. As we move to more automated vehicles, these systems and their functionality will become more complex.

In addition, new RF chains, such as millimeter wave (mmWave), will migrate to cars, providing three times the precision and data transmission rate of current systems. This enables designers to implement smarter in-vehicle communications and sensing, helping cars detect and avoid other cars, pedestrians, objects and devices.

Just as the cellular technology market has experienced ups and downs, the automotive market will not be a smooth transition. Customers will influence vehicle design, regulators will control and influence the technology, and the LTE/5G connected world around the car will continue to advance. RF design engineers must balance performance and opportunities in their applications to meet market demands.

Today’s smartphones have more computing power than NASA had when it sent two astronauts to the moon in 1969. What do we do with all this raw computing power? Network communications, of course!

Modern cars have more computing power and technological complexity than smartphones. Therefore, interference between different technologies and RF signals in modern cars is a constant challenge for design engineers.

To ensure that all of these technologies can coexist, RFFE modules need to combine precise filtering, PA performance, and PA efficiency so that they can work together. In addition, these components must be able to operate in harsh environmental conditions to comply with strict automotive quality standards. Finally, the system requirements of CA and DSDA technologies bring more challenges.

This requires us to first understand the key performance parameters related to RF. It is understood that the key performance parameter challenges related to RF include receiver sensitivity, linearity, selectivity, heat generation and stability.

1. Receiver sensitivity

Receiver sensitivity indicates how weak an input signal a receiver can successfully receive. The lower the power level a receiver can receive, the higher the receiver sensitivity. Receiver sensitivity is usually defined as the smallest input signal required to produce a specified signal-to-noise ratio (SNR) at the receiver's output port.

Receiver (RX) sensitivity is one of the key specifications for any radio receiver in wireless communications. The sensitivity of a receiver represents its ability to pick up low-level signals. Since signal level is inversely proportional to transmission distance, a system with low sensitivity means good reception range. In other words, higher receiver sensitivity equals longer distance.

Receiver sensitivity is defined as the minimum input signal required to produce a specified output signal with a desired signal-to-noise ratio (SNR). It is calculated by multiplying the thermal noise floor by the RX noise figure (NF) and the minimum required SNR. A lower noise figure means better performance.

In automotive, several factors can cause the noise figure to be higher than in other applications or create more SNR challenges. These challenges include:

● In some automotive applications, very long RF coaxial cables may result in increased noise figure and signal loss.

● Extreme temperatures or temperature drift in RF cables and components can cause an increase in noise figure, affecting the performance of RFFE devices.

To reduce the noise figure caused by losses in long cables, designers use low noise amplifiers (LNAs) and try to place the RFFE closer to the antenna. This reduces the cable length, thereby improving the system NF, and reduces the cable insertion loss.

High-Q, low-loss RF filters help reduce the effects of temperature drift. They also help reduce link budget insertion loss and adjacent band interference.

A high Q value (or quality factor) indicates that the ratio of energy loss in the resonator to the energy stored is low. High-Q RF filters have narrower and steeper stopband skirts.

Another design consideration is frequency range. At higher frequencies, it is more difficult to achieve a low noise figure. As cars continue to migrate to higher frequency ranges, such as cellular and Wi-Fi, meeting noise figure specifications becomes more difficult. This trend is unlikely to change, and our expectation is that frequency ranges will gradually extend into the mmWave range, such as 28GHz or 34GHz. Therefore, noise figure will continue to be a major challenge for in-vehicle systems.

2. Linearity

PA linearity describes the ability of a PA to amplify a signal without introducing distortion. This term refers to the primary job of an RF amplifier, which is to increase the power level of an input signal without changing the signal's content.

Linearity is critical for systems that use any frequency modulation scheme to encode information in signal amplitude variations. In telecommunications and signal processing, frequency modulation is the encoding of information in a carrier wave by changing the instantaneous frequency of the wave. These modulation schemes vary from amplitude modulation (AM) to the complex quadrature amplitude modulation (QAM) used in Wi-Fi. The modulation scheme depends on the receiver's ability to discern differences in the amplitude and phase of the signal. To preserve both amplitude and phase variations in the signal, a linear PA must be used. If the transmitted signal is distorted, it is difficult for the receiver to recover the information encoded in the amplitude portion of the modulation. Signal degradation can negatively impact the range and data rate of the system.

The received signal may include unwanted large amplitude out-of-band signals. These unwanted signals can cause distortion in the receiver, reducing the signal-to-noise ratio of the wanted signal, affecting range and data throughput. Filters can be used to suppress these signals and relax linearity requirements. Therefore, using a bandpass filter relaxes the linearity requirements for out-of-band interfering signals.

Nonlinear front-end PA systems can generate spectral regrowth, which can interfere with adjacent channels. Spectral regrowth is a significant distortion mechanism in nonlinear devices such as PAs in wireless applications. Increasing power level requirements, temperature, and link budgets can all lead to linearity issues. The use of bandedge filters can help reduce nonlinear distortion caused by interference from adjacent channel users. In addition, coexistence filters on the RFFE receive side can also reduce signal interference and help improve receiver band signal-to-noise ratio.

3. Selectivity

Selectivity is a measure of how well a radio receiver responds to only the signal to which it is tuned, while rejecting other signals of similar frequency (such as another broadcast on an adjacent channel).

Automotive wireless communication systems can be affected by a variety of interference. Automotive RF design engineers must consider both internal and external RF signals around the radio receiver.

Filters improve receiver selectivity by attenuating unwanted signals while passing wanted signals with minimal loss. They also help reduce adjacent band interference. As the average number of bands and radios in cars increases, and as the number of standards grows, utilizing advanced filter technology such as low drift BAW filters can help engineers address interference challenges.

Reducing heat is another consideration in the wireless RFFE design of automotive systems. Using high-Q RF filtering technology can reduce the impact of heat on insertion loss. As shown in Figure 4-1, using high-Q low-drift filtering technology can help reduce interference during thermal drift. Low-drift filters have a low temperature coefficient of frequency (TCF), which helps reduce insertion loss, reduce adjacent channel interference, and reduce link budget constraints.

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4. Heat generation and stability

Temperature excursions in automobiles can be very large. Automotive stress conditions vary from –40°C to 150°C. Therefore, automotive design engineers and suppliers must validate and test components and systems for these extreme conditions (see Figure 4-2).

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In system design, engineers often have to make trade-offs between linearity, power output, and efficiency. Heat can degrade overall system performance, such as throughput, signal range, and interference suppression. Therefore, it is important to design the system using RFFE components that reduce heat. Using optimized high-linearity power amplifiers or front-end modules can reduce overall heat generation.

Another important factor affecting heat in the car is cable loss. Cable loss increases the link budget, which means that the transmit (TX) RFFE PA must compensate by increasing the output power to reduce the loss. As the output power increases, the system heats up and the efficiency decreases.

Learn about other automotive RF challenges

In automotive RF systems, in addition to performance parameters, there are two important topics to consider:

Develop components that meet stringent Automotive Electronics Council (AEC) automotive quality standards.

Meet the system requirements for carrier aggregation (CA) and DSDA technologies.

1. Comply with IATF and AEC standards

As automotive technology advances toward more advanced driver assistance systems and autonomous vehicles, the stakes will increase. The automotive industry has developed stringent quality standards for component manufacturing and testing to ensure that increasingly complex RF components do not fail once they are embedded in electronic systems.

Throughout the manufacturing and testing process, automotive industry manufacturers must meet specified industry standards. Three key standards include:

● International Automotive Task Force (IATF) 16949: This quality management system standard for the automotive industry is used worldwide. Automakers generally assume that component manufacturing, assembly and testing companies should be accredited to the IATF 16949 standard.

● Automotive Electronics Council (AEC) Q100: Specifies standard testing for active components such as switches and PAs.

● AEC-Q200: Specifies standard testing for passive devices such as RF filters used in Wi-Fi communications and cellular communications.

Some tests are limited to the automotive industry, such as the Early Life Failure Rate (ELFR) test, which requires exposing multiple samples (each sample contains 800 components) to an environment of at least 125°C, and the Power and Temperature Cycle (PTC) test, which requires exposing the samples to an environment with alternating high and low temperature cycles, ranging from –40°C and below to 125°C.

Other tests are performed under more severe conditions or in larger batches to provide better statistical basis for judging whether production components are reliable.

2. CA and DSDA

Carrier aggregation (CA) allows mobile network operators to combine many individual LTE carriers together to increase bandwidth and bit rates. Carrier aggregation is a technique used to combine multiple LTE component carriers (CCs) of available spectrum to provide a single LTE network.

● Support wider continuous or non-contiguous intra-band or inter-band bandwidth signal blocks

● Improve network performance in uplink, downlink or both directions

● Increase peak data rates to 1 GB/sec (Gbps) Peak loading speed

● Increase the overall capacity of the network to take advantage of fragmented spectrum allocations

A component carrier (CC) is an LTE channel that is typically assigned to one user. This is a serious challenge for RF designers. In cars, CA will provide Gigabit-class LTE connectivity. To achieve these speeds, the in-vehicle modem uses advanced digital signal processing (256 QAM) and 4x4 MIMO, supporting up to 4 carrier aggregations.

MIMO is an antenna technology for wireless communications that uses multiple antennas at both the transmitter and receiver. The antennas at each end of the communication circuit are combined to minimize errors and optimize data speeds.

CA challenges in automobiles include:

● Downlink sensitivity: Many CA applications require architectures that use RF filters, duplexers, or complex multiplexers. These RF filters help ensure isolation between the various TX and RX paths, helping achieve system sensitivity. As more bands are added to the system, using more complex filtering (such as multiplexers), designers must ensure that the various bands work together.

● Harmonic Generation: Harmonics are generated by nonlinear components such as PAs, duplexers, and switches. Designers must carefully make trade-offs in their designs to ensure that performance is not compromised when electrical harmonics are mitigated.

● Desensitization: Harmonics and TX leakage lead to a reduction in system sensitivity, known as desensitization. Desensitization is the reduction in sensitivity due to noise sources, which are usually generated by the same radio equipment. This causes the receiver to perform poorly, preventing the proper detection of the target signal. High switch isolation and filter attenuation can minimize interference between signal paths.

DSDA technology uses two independent transceivers and antenna paths in two active CCs. This enables OEMs to take advantage of specific contracted carrier services while giving car owners the ability to add their favorite carriers. Carriers allow car owners to add their cars to their home data plans and benefit from them. The downside is that DSDA increases system power consumption, which increases heat, and also increases RFFE complexity. To reduce heat, designers must use linear and efficient RFFE blocks.

Like CA, DSDA also requires stable, low-drift filtering to achieve system and automaker design goals. As the number of CCs increases, the importance of individual band filters and complex multiplexers also increases.