Analog Technology: Key Technology in the IoT

This June, the semiconductor industry released two notable news items.

In its 2022 McClean Report Q2 update released in May, IC Insights mentioned that Taxes Instruments continues to maintain its solid position as the world's leading analogue IC supplier with $14.1 billion in analogue sales and a 19% market share in 2021.

The second piece of news is that the problem of tight global analogue chip supply will turn around in the second half of this year, as TI said that by the third quarter, the company's chip capacity crunch would be eased. For this reason, the industry will be interpreted as follows: if the second half of TI's production capacity is improved, the supply of the entire analogue chip industry will be eased, and chip prices will also fall. In almost all digital-centric systems, analogue IC is still a key component. Generally speaking, the analogue IC market growth/decline is slower than the overall IC market growth/decline, but the market situation in 2021 is the opposite. In its (2022 McClean Report) Q1 report, IC Insights pointed out that the new crown virus outbreak in 2020 had a huge impact on the global economy. However, the analogue IC market in 2021 market saw an unprecedented 30% surge, corresponding to a 26% increase in the overall IC market. Analog ICs are expected to achieve another double-digit market growth of 12% in 2022, with total sales of about $83.2 billion and shipments growing by 11% to reach 238.7 billion.

Last year's analogue IC market is likely to be remembered because of the strength and breadth of the outstanding growth. 2021 sales of the entire analog market hit a record high of $74.1 billion, according to IC Insights. The top 10 global analogue suppliers accounted for 68 per cent of sales. Strong demand combined with supply chain disruptions led to a 6% increase in the average selling price (ASP) of analog ICs last year. Before that, the years of ASP growth for analog products went back 17 years to 2004. 2022 is expected to see sales growth in the major general analogue and application-specific analogue market categories tracked by IC Insights, with segment amplifiers and comparators growing about 7 per cent, for example, and automotive application-specific analogue ICs growing as much as 17 per cent.

Analog Technology: A Key and Indispensable Technology in the Internet of Things

Many people think that much of today's Internet of Things (IoT) innovation is focused on digital technologies. From the well-known cloud computing to the hot edge intelligence in recent years, the role of digital technology in driving this is obvious to all. However, in the discussion, perhaps we all overlooked that the edge of IoT is still actually analogue, and the system must resort to detection schemes such as light, pressure, temperature, location, etc., to obtain critical data. In other words, the IoT is a series of actions taken after the intelligent processing of data generated from analogue sources, i.e., analogue components + digital connectivity and processing = effective IoT deployment.

Because analogue sits at the edge of the network, the quality of the analogue layer ultimately determines the quality of everything else in the system. A noisy analogue front end can distort digital information and significantly impact the overall system. Digital applications will only be better if the analogue part is done right. In addition, digital information must also be accurately converted back to analogue signals at the edge for IoT applications that control the flow. While design engineers generally agree that most new products developed to support the IoT are in the digital domain, analogue technology will continue to play a key role in the IoT for many years.

The signal chain is the foundation of analogue technology, which aims to collect and process data based on real-time information analysis. Usually, analogue signal chain products are integrated circuits that can send and receive, convert, amplify, filter and other processing capabilities of analogue signals. According to the function, analogue signal chain chips can be divided into linear products, converter products, interface products, clock and timing products, etc. Among them, linear products mainly include amplifiers and comparators. Converters are analogue-to-digital converters (ADCs) and digital-to-analogue converters (DACs).

Design considerations for analogue signal chain products

In IoT, sensing signals are related to infinitely variable physical parameters such as temperature, light, pressure, proximity, speed and touch, and fluids and liquids (including smoke, gases, etc.). The sensor outputs are voltage or current signals of small amplitude, which are difficult to convert directly to digital signals and must be conditioned before conversion. Here the signal conditioning technology is the sensor output analogue signal after amplification, filtering, linearization compensation, isolation, protection and other measures to make it suitable for analogue / digital converter (ADC) input. The use of key signal conditioning techniques can improve the overall performance and accuracy of a data acquisition system by a factor of 10.

The signal chain starts with sensors that sense the analogue world, followed by signal amplifiers, data converters, interfaces, and clock and timing circuits. The successful operation of an IoT device depends heavily on the selection of parameters for these devices. Next, we will discuss the selection of the two key devices, amplifiers and data converters, in IoT devices.

Operational Amplifier Selection

As already mentioned, it is important to ensure the accuracy of the signal before collecting information such as pressure, temperature, vibration and light and transferring it to the digital domain. To obtain the best signal-to-noise ratio (SNR), we must design a low-noise analogue front-end and an ADC that can accurately capture the sensor signal. Although devices are now increasingly integrated, engineers sometimes use separate operational amplifiers instead of integrated analogue front ends to give more control and flexibility to the design. The major op-amp IC suppliers in the market are ADI, TI, STMicroelectronics (ST), ROHM, Microchip, Renesas and NXP, and they offer tens of thousands of products to the market for designers to choose from.

When looking for the best op-amp, designers must fully consider whether the amplifier will degrade the performance of the ADC or DAC, as well as the signal range, gain, static and dynamic loads, and supply voltage. The following are a few of the more cost-effective op-amps on the market.

ST TSV772 Operational Amplifier

ST's TSV772 op-amp is a dual op-amp that is part of the company's high-performance 5V op-amp family and can operate at low voltages of 2V, with rail-to-rail input and rail-to-rail output, gain bandwidth product (GBW) of 20MHz, stable unit gain, swing rate of 13V/µs, input voltage noise of 7nV/Hz, and 4kV ESD protection (HBM), making it a powerful The TSV772 features an output capacitance of 47pF, simplifying its use as an A/D converter input buffer. The device can even operate with deeply discharged batteries, and recommended applications include smoke detectors, solar generators, telecom infrastructure equipment, and computer servers.

ADI ADA4077-2 Dual-Channel Amplifier

ADI's ADA4077-2 dual-channel amplifier is a high-precision operational amplifier designed for processing, chemical and environmental monitoring, motor control, and more. The ADA4077-2 has a typical bandwidth of 3.9MHz at 1kHz and voltage noise of 7nV/rtHz. Typical power consumption is only 400µA at 25°C with a nominal supply voltage of ±15Vdc. The device is available in two grades for bias and thermal drift, providing design engineers with the flexibility to meet budget and packaging requirements. The ADA4077-2 is considered an ideal front-end amplifier for designing sensor interfaces for applications such as process control input modules.

TI OPAx320/OPAx320-Q1 COS operational amplifier

TI's OPAx320/OPAx320-Q1 COS operational amplifier is ideal for low-power, single-supply applications with low noise (7nV/Hz) and high-speed operational characteristics, very suitable for driving sampling ADCs, but also for applications such as signal conditioning and sensor amplification. The TI op amps are designed with a zero-crossover distortion linear input stage. They have an excellent common-mode rejection ratio (CMRR) of 114 dB, typical over the entire input range. The OPAx320/OPAx320-Q1 has a wide supply voltage range of 1.8V to 5.5V, with an excellent supply rejection ratio (106dB) over the entire supply range.

TI's TLV9061 is a single 5.5V with rail-to-rail input and output swing capability if you are looking for a small op-amp. The device is inexpensive, small in size, and designed for low-voltage operation (1.8V to 5.5V) with performance specifications similar to the OPAx316 and TLVx316 devices. Applications include electric bicycles, smoke detectors, heating, ventilation and air conditioning (HVAC), motor control, wearable devices, sensor signal conditioning, bar code scanners, and more.

A/D converter selection

Designing mixed and analogue signals introduces more complexity than some digital circuits. The purpose of an A/D converter is to quantize the input, which means that the converter introduces a small amount of error. The overall performance of an A/D converter is a reflection of several parameters such as thermal noise, jitter, and quantization noise. The three most popular ADC architectures on the market today are successive approximation (SAR) ADCs, ∑-Δ ADCs and Pipeline ADCs, with thousands of corresponding products available. It seems to be a daunting task to select the right ADC for a specific application. In IoT devices, a large part of the solution can be accomplished by successive approximation (SAR) ADCs and ∑-Δ ADCs.

ADI AD7983 Analog-to-Digital Converter

ADI's AD7983 analogue-to-digital converter is a 16-bit, successive approximation (SAR) ADC with a single power supply. It has a built-in low-power, high-speed, 16-bit sampling ADC and a multifunction serial interface port. On the rising edge of CNV, the device samples the analogue input voltage difference between IN+ and IN- from 0 V to REF. The reference voltage (REF) is provided externally and can be independent of the supply voltage (VDD). Power consumption varies linearly with the throughput rate. The SPI-compatible serial interface is also capable of several daisy-chaining ADCs to a three-wire bus using SDI inputs and provides an optional busy indication. Ideal for battery-powered devices, data acquisition, and other applications.

TI ADS1278 Analog-to-Digital Converter

TI's ADS1278 analogue-to-digital converter is a 24-bit, 144kSPS 8-channel synchronous sampling Δ-sigma ADC for wide-bandwidth applications, which has multiple independent high-order chopper-stabilized modulators and FIR digital filters integrated internally to achieve 8-channel synchronous sampling, supporting high-speed, high-precision, low-power, low-speed four operating modes. At the same time, the ADS1278 has excellent AC and DC characteristics, with a sampling rate of up to 128Ks/s, a signal-to-noise ratio of 111dB at 62kHz bandwidth, and an offset drift of 0.8μV/℃. The data output is available with frame synchronous or SPI serial interfaces, each supporting daisy-chain connection, which can be applied to demanding multi-channel signal acquisition systems such as vibration analysis, medical monitoring, and dynamic strain measurement equipment.

To save development time, designers can also use TI's ADS1278EVM-PDK evaluation module, a complete evaluation/demo kit that combines the ADS1278EVM with a DSP-based MMB0 board as a motherboard. The kit includes the motherboard and ADCPro evaluation software and can be used with a PC running the Microsoft Windows operating system to enable complete evaluation of the ADS1278 device.

Final words

While current digital IoT edge devices can handle multiple tasks simultaneously, analogue sensors are still limited to signal enhancement functions in most cases. However, it is precise because the accuracy requirements of analogue signals are closely related to IoT applications that the importance of analogue technology in the IoT is reinforced. Perhaps this is why designers of analogue and digital technologies across the board are in high demand.

Sensors, amplifiers, and data converters are the devices that collect and transmit data, and their presence fuels the broader application prospects of IoT. As the starting point for the IoT, IoT engineers need to understand that the engineering challenge is to control signal fidelity, amplification and filtering before digitization, so whether it's a differential amplifier, operational amplifier or other amplifier, designers must master the fundamentals of amplifiers.

On the other hand, while some digital sensors in the IoT have achieved very high levels of integration, and integrated ADCs can both reduce development effort and cost and reduce the power required to drive the device, it is undeniable that local analogues can often represent the data source more accurately. The role of the separate A/D converter remains critical.

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