Smart Batteries with Sensors

Quick-charging batteries are in vogue now. Consumers are demanding more compact, quick-charging, lightweight, and high-energy-density batteries for all types of electronic devices including high-efficiency vehicles. Whatever be the working conditions, even during a catastrophe, batteries must be safe. Of late, the Lithium-ion battery technology has gained traction among designers and engineers as it satisfies several demands of consumers, while at the same time being cost-efficient. However, with designers pushing the limits of Li-ion battery technology capabilities, several of these requirements are now conflicting with one another.

While charging and discharging a Li-ion battery, many changes take place in it, like in the mechanics of its internal components, in its electrochemistry, and its internal temperature. The dynamics of these changes also affect the pressure in its interface within the housing of the battery. Over time, these changes affect the performance of the battery, and in extreme cases, can lead to reactions that are potentially dangerous.

Battery designers are now moving towards smart batteries with built-in sensors. They are using piezoresistive force and pressure sensors for analyzing the effects charging and discharging have on the batteries in the long run. They are also embedding these sensors within the battery housing to help alert users to potential battery failures. Designers are using thin, flexible, piezoresistive sensors for capturing relative changes in pressure and force.

Piezoresistive sensors are made of semi-conductive material sandwiched between two thin, flexible polyester films. These are passive elements acting as force-sensitive resistors within an electrical circuit. With no force or pressure applied, the sensors show a high resistance, which drops when the sensor has a load. With respect to conductance, the response to a force is a linear one as long as the force is within the range of the sensor’s capabilities. Designers arrange a network of sensors in the form of a matrix.

When two surfaces press on the matrix sensor, it sends analog signals to the electronics, which converts it into a digital signal. The software displays this signal in real-time to offer the activity occurring across the sensing area. The user can thereby track the force, locate the region undergoing peak pressure, and identify the exact moment of pressure changes.

The matrix sensors offer several advantages. These include about 2000-16000 sensing nodes, element spacing as low as 0.64 mm, capable of measuring pressure up to 25,000 psi, temperature up to 200 °C, and scanning speeds up to 20 kHz.

Designers also use single-point piezoresistive force sensors for measuring force within a single sensing area. They integrate such sensors with the battery as they are thin and flexible, and they can also function as a feedback system for an operational amplifier circuit in the form of a voltage divider. Depending on the circuit design, the user can adjust the force range of the sensor by changing its drive voltage and the resistance of the feedback. This allows the user complete control over measuring parameters like maximum force range, and the measurement resolution within the range. As piezoresistive force sensors are passive devices with linear response, they do not require complicated electronics and work with minimum filtering.

Using RTDs for Measuring Temperature

Much industrial automation, medical equipment, instrumentation, and other applications require temperature measurement for monitoring environmental conditions, correcting system drift, or achieving high precision and accuracy. Many temperature sensors are available for use like electronic bandgap sensors, thermistors, thermocouples, and resistance temperature detectors or RTDs.

The selection of the temperature sensor depends on the temperature range to be measured and the accuracy desired. The design of the thermometer also depends on these factors. For instance, RTDs provide an excellent means of measuring the temperature when the range is within -200 °C to +850 °C. RTDs also have very good stability and high accuracy of measurement.

The electronics associated with using RTDs as temperature sensors with high accuracy and good stability must meet certain criteria. As an RTD is a passive device, it does not produce any electrical signal output on its own. The electronics must provide the RTD with an excitation current for measuring its resistance. This requires a small but steady electrical current passing through the sensor for generating a voltage across it.

The design of the electronics also depends on whether the design is using a 2-, 3-, or 4-wire sensor. This decision affects the sensitivity and accuracy of the measurement. Furthermore, as the variation of resistance of the RTD with temperature is not linear, the electronics must condition the RTD signal and linearize it.

RTDs in common use are mostly made of platinum, and their commercial names are PT100 and PT1000. These are available in 2-wire, 3-wire, and 4-wire configurations. Platinum RTDs are available in two shapes—wire wound and thin-film. Other RTD types available are made from copper and nickel.

When using an RTD as a temperature sensor, its resistance varies as a function of the temperature, and not in a linear manner. However, the variation is very precise. To linearize the output of the RTD, the electronics must apply a standardizing curve, the most common standardizing curve for RTDs is the DIN curve. This curve defines the resistance versus temperature characteristics of the RTD sensor and its tolerance within the operating temperature range.

Using the standardizing curve helps define the accuracy of the sensor, starting with a base resistance at a specific temperature. Usually, this resistance is 100 ohms at 0 °C. DIN RTD standards have many tolerance classes, which are applicable to all types of platinum RTDs in low power applications.

The user must select the RTD and its accuracy for the specific application. The temperature range the RTD can cover depends on the element type. The manufacturer denotes its accuracy at calibration temperature, usually at 0 °C. Therefore, any temperature measured below or above the specified temperature range of the RTD will have lower accuracy and a wider tolerance.

The categorization of RTDs depends on their nominal resistance at 0 °C. Therefore, a PT100 sensor at 0 °C has a resistance of 100 ohms, while at the same temperature a PT1000 sensor has a resistance of 1000 ohms. Likewise, the temperature coefficient at 0 °C for a PT100 sensor is 0.385 ohms/°C, while that for the PT1000 is ten times higher at the same temperature

Advanced Materials for Magnetic Silence

High-performing advanced magnetic materials are now available that help to handle challenges in hybrid/electrical vehicles. These are challenges related to conducted and radiated electromagnetic interference. Automotive engineers are encountering newer challenges with fully electric vehicles or EVs and hybrid electric vehicles or HEVs become more popular.

The above challenges are so intriguing, engineers now have a fundamental discipline for it, noise vibration and harshness or NVH engineering. Their aim is to minimize NVH for ensuring not only the stability of the vehicle but also the comfort of the passengers.

With electric vehicles becoming quieter, several NVH sources that the noise of the internal combustion engine would mask, are now easily discernible. Engineers divide the root cause of the NVH problems in electric vehicles into vibration, aerodynamic noise, mechanical noise, and electromagnetic noise.

For instance, cabin comfort is adversely affected by electromagnetic noise from auxiliary systems such as the power-steering motor and the air-conditioning system. This can also interfere with the functioning of other subsystems.

Likewise, there is electromagnetic interference from the high-power traction drive system. This interference produces harmonics of the inverter switching and power supply frequencies. Moreover, the interference also induces electromagnetic noise within the motor as well.

With the battery frequently charging and discharging when the EV is in operation, combined with various electromagnetic noises like radiated noise, common-mode noise, and differential noise move through the transmission lines.

All the above reduce the cabin comfort in the vehicle while interfering with systems that help manage the combustion engine in an HEV.

As with many engineering projects, NVH issues are also specific to particular platforms and depend on the design of several structural components, the location of subsystems related to one another, and the design of isolating bushes and mountings. Engineers must deal with most NVH issues related to EMI by applying best practices in electrical engineering for attenuating high-frequency conducted and radiated interference as they couple onto cables and reach various subsystems. Engineers use cable ferrites for preventing long wires from acting as pickups or radiating aerials. They also use inline common-mode chokes for attenuating EMI entering signal and power lines by conduction.

For automotive applications, such cable chokes and ferrites must meet exacting criteria.  Major constraints for these components are their weight and size. Common-mode chokes must provide noise suppression through excellent attenuation properties while using a small physical volume. Additionally, they need to suppress broadband noise up to high operating temperatures, while maintaining high electrical and mechanical stress resistance.

To help with manufacturing such as maintaining high levels of productivity, there are further requirements of robustness and easy handling on assembly lines. This ensures each unit reaches customers in perfect condition. New materials meet the above requirements while offering enhanced characteristics.

The new class of materials is Nanocrystalline cores that engineers classify as metals and they help with eliminating low-frequency electromagnetic noise. Cable ferrites and choke cores made of these materials are much smaller than those made from conventional materials like ceramic ferrites. They also deliver superior magnetic performance, presenting a viable solution for challenging automotive and e-NVH issues.

New Battery Technology for UPS

Most people know of the Lithium-ion battery technology in use mainly due to their overwhelming presence in mobile sets. Those who use uninterruptible power supplies for backing up their systems are familiar with the lead-acid cells and the newer lithium-ion cells. Another alternative technology is also coming up mainly for mission-critical facilities such as for data centers. This is the Nickel-Zinc technology, and it has better trade-offs to offer.

But the Nickel-Zinc battery technology is not new. In fact, Thomas Edison had patented it about 120 years ago. In its current avatar, the Nickel-Zinc battery offers superior performance when used in UPS backup systems. They offer better power density, are more reliable, safe, and are highly sustainable.

For instance, higher power density translates into smaller weight and size. This is the major difference between a battery providing energy and a battery providing power. In a data center, the UPS must discharge fast for a short period for maintaining operational continuity. This is what happens during brief outages, or until the backup generators spin up to take over the load. This is the most basic power battery operation, where the battery must deliver a high rate of discharge, and it does so with a small footprint.

On the other hand, Lead-acid and Lithium-ion technologies offer energy batteries. Their design allows them to discharge energy at a lower rate for longer periods. Electric vehicles utilize this feature, and the automotive industry is spending top dollars for increasing the energy density of such EV batteries so that the user can get more mileage or range from their vehicles. This is not very useful for data center backup, as the battery must have a higher energy storage footprint for supporting short duration high power output requirements.

This is where the Nickel-Zinc battery technology comes in. With an energy density nearly twice that of a Lead-acid battery, Nickel-Zinc batteries take up only half the space. Not only is the footprint reduced by half, but the weight also reduces by half for the same power output. As compared to Lithium-ion batteries, Nickel-Zinc batteries not only excel in footprint reduction, but they charge at a faster rate while retaining thermal stability. This feature makes them so useful for mission-critical facility uptime.

Nickel-Zinc batteries have proven their reliability as well. They have clocked over tens of millions of operating hours for providing uninterrupted backup power in mission-critical applications. Another feature very useful for data center operations is the battery string operations of the Nickel-Zinc technology.

When a Lithium-ion or a Lead-acid battery fails, the battery acts as an open circuit, preventing other batteries in the string from transferring power. On the other hand, a weal or a failed Nickel-Zinc cell remains conductive, allowing the rest of the string to continue operations, with a lower voltage. In emergency situations, this feature of the Nickel-Zinc battery is extremely helpful, as the faulty battery replacement can proceed with no operational impact and at a low cost.

In parallel operation also, Nickel-Zinc batteries are more tolerant of string imbalances, thereby maintaining constant power output at significantly lower states of health and charge as compared to batteries of other technologies.

Power Transmission Through Lasers

Wireless power transfer has considerable advantages. The absence of transmission towers, overhead cables, and underground cables is the foremost among them, not to exclude the expenses saved in their installation, upkeep, and maintenance. However, one of the major hurdles to wireless power transmission is the range it can cover. But now, Ericsson and PowerLight Technologies have provided a new proof of concept project that uses a laser beam to transmit power optically to a portable 5G base station.

Wireless power transmission is not a new subject to many. People use wireless power for charging many devices like earbuds, watches, and phones. But the range in these chargers is short, as the user must place the device on the pad of the charger. This limits the usefulness of the wireless charging station for transmitting power. Although labs have been experimenting with larger setups that can charge devices placed anywhere within a room, reports of beaming electricity outdoors and for long distances have been rather scarce.

PowerLight has been experimenting with wireless power transfer for quite some time now, and they have partnered with Ericsson, a telecommunications company, for a proof of concept demonstration. Their system consists of two components, a laser transmitter, and a receiver. The distance between the transmitter and receiver can vary from a few hundred meters to a few thousand meters.

However, unlike a Tesla coil, the PowerLight device does not transmit electricity directly. Instead, at the transmitter end, electricity powers a powerful laser beam, sending it directly to the receiver. In turn, the receiver uses specialized photocell arrays to convert the incoming laser back into electricity for powering connected devices.

Such a powerful laser-blasting through the open air can be a dangerous thing. Therefore, PowerLight has added many safeguards. They surround the beam with wide cylinders of sensors that can detect anything approaching. The sensors can shut off the beam within a millisecond, if necessary. In fact, the safety system is so fast that a flock of birds is not affected when flying through the laser beam, but there is an interruption at the receiver.  To overcome such fleeting interruptions, and cover longer-term disruptions as well, the PowerLight system has a battery back-up at the receiver end.

PowerLight is using their system to power a 5G radio base station from Ericsson, that has no other power source connected to it. The base station received 480 watts from the transmitter placed at a distance of 300 m. However, according to the PowerLight team, the technology can send 1000 watts over a distance of over 1 km. They also claim there is room for future expansions.

Wirelessly powering these 5G units could make them more versatile, as they will then become portable, and capable of operating in temporary locations. This will also allow them to operate in disaster areas, where there has been a disruption of infrastructure.

According to PowerLight, their optical power beaming technology may be useful in several other applications also, such as for charging electric vehicles, in future space missions, and in adjusting the power grid operations on the fly.

TI Driver for BLDC Motors

When simple motors were more frequently used, it was relatively easy to design products with them. Controlling such motors was simple, whether it was a brushed DC motor or a single-phase AC motor. There was no need for sophisticated hardware or software for designing a product with a motor.

However, sophisticated BLDC or brush-less DC motors are replacing most of the above motors because of several advantages like quiet operation and high efficiency. But these advantages come at the cost of design knowledge and effort, requiring both hardware and software development. Texas Instruments has developed a new integrated circuit that allows designers to achieve all the benefits easily from these motors.

The biggest benefit offered by BLDC motors over older designs is their improved power efficiency. Most government regulators today demand that electrical products meet strict efficiency standards. In most cases, meeting these requirements is possible only through the use of BLDC motors.

Motors are mechanical devices and therefore, they make noise when operating. Although the quiet operation is not usually a design goal for most products, using a BLDC motor offers a way to achieve low noise operation.

There are further advantages to using BLDC motors. One of them is low voltage operation, and the other is a longer life. Manufacturers of BLDC motors are now offering them in larger sizes for use in bigger products.

As stated earlier, BLDC motors are now replacing brushed DC motors and in some cases, AC motors as well. Some practical examples are robotic vacuum cleaners, pumps, fans, washing machines, humidifiers, and air purifiers. They are useful for multiple automotive devices as well.

Functionally, a BLDC motor works under the same principles that govern the operation of all motors—rotation is from the interaction of two magnetic fields, one fixed and the other movable. Frequently, the BLDC motor will have multiple stator coils embedded in the periphery of the motor assembly. With the stator coil wired into three groups, it performs as a three-phase motor does. The rotor on the BLDC motor consists of several permanent magnets rotating in the circle formed by the stator coils. The user only has to apply a sequence of pulses to the stator coils.

The timing of the pulses must match their interaction with the permanent magnets. The control circuitry that drives the stator coils gets the correct timing from multiple sensors indicating the orientation of the rotor. These sensors are mostly Hall-effect devices that produce signals that the controller requires for moving the magnetic fields on the stator coil.

There are numerous variations of the approach to control the BLDC motor. One of them is a sensor-less method using the back electromotive force the rotating rotor magnets induce into the stator coils. The sensor-less method typically reads the feedback voltages in the motor stator winding and processes them into control signals.

Many motor controllers are pre-programmed and packaged BLDC motor control modules. This is usually satisfactory for common applications. Others, however, require a custom design. The MCF8316A from TI is a single chip BLDC motor controller chip that only requires inputs for speed, direction, and torque. The IC takes care of the rest.

Where Do You Use Encoders?

All kinds of mechanical systems use a critical component commonly known as an encoder. Large industrial machines performing delicate work, high-precision prototyping, or repeatable tasks use encoders predominantly. Production of advanced electronics also requires the use of encoders. Encoders can be linear, angle, or rotary and the electronics sector uses them in some form or the other. Semiconductor fabrication, with its small components and work areas, requires encoders of the highest resolution and accuracy.

Production of electronics often uses vacuum environments with unique ventilation. These environments require special types of encoders, including linear and angle types made specifically to operate with the temperature and gaseous conditions prevalent with vacuum environments.

CNC machines must maintain their accuracy and position even when operating with heavy spindles and workpieces, high speeds, and multi-axis movements. All the components need to work together for accurate milling, drilling, and boring. Encoders play an important role in the synchronous working of CNC machines. For instance, custom linear encoders guide the travel of the axes of a milling machine.

At present, the automation industry is striding ahead rapidly and requires capable encoders. Strausak, a grinding machine company, makes robotic arms that manufacturing environments use universally. Unmanned mechanical systems must rely on accurate and consistent measurement and motion provided by encoders.

Automated transportation, such as high-speed trains in Sweden, depends on custom-made absolute encoders. These encoders operate a redundant system for automatically controlling the speed and braking of the train when necessary.

The medical industry requires precision and accuracy along with safety for testing and treating the human body while developing new procedures in the lab. CT and MRI scanning machinery use exposed linear and rotary encoders for precision imaging and maintaining patient safety. Precision angular and linear encoder technology help radiation therapy, leaving no room for error.

For instance, GammaPod, the most advanced breast cancer treatment in the world, depends on absolute rotary encoders for operating its stereotactic radiotherapy system. The medical industry depends on encoders predominantly because of the precision necessary for safely and accurately testing and treating the human body.

Robotics often uses articulating arms for picking and placing objects and equipment in manufacturing plants. They also use mobile, guided, and automated robots, which, in turn, require encoders for their proper functioning. For instance, encoders provide automated systems with the necessary and effective position and speed feedback for allowing them to function with minimum human intervention. Robotics often uses low-profile encoders that can fit inside small robotic arms.

All types of encoders are available for serving the general purpose of measuring motion and providing signaling feedback. However, their capabilities, configurations, and applications vary significantly and widely. In every facet of life, encoders play a significant role. This is especially applicable in the industrial and technological world, where safety, accuracy, and precision are important parameters to uphold.

Knowledge of the encoder transfer function is important for selecting the proper resolution for incremental optical encoders and for tuning the regulator depending on the speed and torque of the application. The implementation of a proper control loop impacts the stability and performance of the application.

Battery Electrolyte from Wood

Although there exist several types of batteries, all of them function with a common concept—batteries are devices that store electrical energy as chemical energy and convert this chemical energy into electricity when necessary. Although it is not possible to capture and store electricity, it is possible to store electrical energy in the form of chemicals within a battery.

All batteries have three main components—two electrodes or terminals made of different metals, known as anode and cathode, and the electrolyte separating these terminals. The electrolyte is the chemical medium allowing the flow of electrical charges between the terminals inside the battery, When a load connects to a battery, such as an electrical circuit or a light bulb, a chemical reaction near the electrodes creates a flow of electrical energy through the load.

The most commonly used battery today, the lithium battery, typically uses a liquid electrolyte for carrying electrical charges or ions between its electrodes. Scientists are also looking at alternatives like solid electrolytes for future opportunities. A new study offers cellulose derived from wood as one type of solid electrolyte. The advantage of this solid electrolyte from wood is its paper-thin width, allowing the battery to bend and flex for absorbing stress while cycling.

The electrolyte presently in use today in lithium cells has the disadvantage of containing volatile liquids. There is thus a risk of fire in case the device short-circuits. Moreover, there is the possibility of the formation of dendrites—tentacle-like growths—and this can severely compromise the battery’s performance. On the other hand, solid electrolytes, made from non-flammable materials, allow the battery to be less prone to dendrite formation, thereby opening up totally modern possibilities with different battery architecture.

For instance, one of these possibilities involves the anode, one of the two electrodes in the battery. Today’s batteries usually have an anode made from a mix of copper and graphite. With solid electrolytes, scientists claim they can make the battery work with an anode made from pure lithium. They claim the use of pure lithium anode can help to break the bottleneck of energy density. Increased energy density will allow planes and electric cars to travel greater distances before recharging.

Most solid electrolytes that scientists have developed so far are from ceramic materials. Although these solid electrolytes are very good at conducting ions, they cannot withstand the stress of repeated charging and discharging, as they are brittle. Scientists from the University of Maryland and Brown University were seeking an alternative to these solid electrolytes, and they started with cellulose nanofibrils found in wood.

They combined the polymer tubes they derived from wood with copper. This formed a solid ion conductor with conductivity very similar to that in ceramics, and much better than that from any other polymer ion conductor. The scientists claim this happens as the presence of copper creates space within the cellulose polymer chains allows the formation of ion superhighways, enabling lithium ions to travel with substantially high efficiency.

With the material being paper-thin and thereby highly flexible, scientists claim it will be able to tolerate the stresses of battery cycling without damage.

Improving Computer Vision with Two AI Processors

Computer vision is becoming a necessity in IoT and automotive applications. Engineers are trying for the next level in computer vision with two AI processors. They hope that two AI processors will help to make computer vision not only more efficient but also more functional.

One of the fastest-growing applications of artificial intelligence, computer vision is jostling for attention between prestigious fields like robotics and autonomous vehicles. In comparison to other artificial intelligence applications, computer vision has to rely more on the underlying hardware, where the underlying imaging systems and processing units overshadow the software performance.

Therefore, engineers are focusing on cutting-edge technology and state-of-the-art developments for the best vision hardware. Two companies, Intuitive and Syntiant, are now making headlines by supporting this move.

Israeli company, Intuitive, recently announced that its NU4000 edge Artificial Intelligence processor will be used by Fukushin Electronics in their new electric cart, POLCAR. The processor will allow the cart to have an integrated obstacle detection unit.

Requiring top performance and power efficiency when operating a sophisticated object detection unit in a battery-powered vehicle like an electric cart made Fukushin use the NU4000. The edge AI processor from Intuitive is a multicore System on a Chip or SoC that can support several on-chip applications. These include computer vision, simultaneous localization and mapping or SLAM, and 3d depth-sensing.

The NU4000 achieves these feats by integrating three Vector Cores that together provide 500 COPS. There is also a dedicated CNN processor offering three CPUs, 2 TOPS, a dedicated SLAM engine, and a dedicated depth processing engine. Intuitive has built this chip with a 12nm process, and it can connect up to two displays and six cameras with an LPDDR4 interface.

With a small form factor and low power consumption, the NU4000 is a powerful processor providing several key features that could make the obstacle detection unit a special application for Fukushin’s POLCAR.

California-based Syntiant was in the news with their Neural Decision Processor, the new NDP200. Syntiant has designed this processor for applications using ultra-low-power, especially useful for deep learning. With a copyrighted Syntiant core as its core architecture, it has an embedded processor, the ARM Cortex-M0. With this combination, the NDP200 achieves operating speeds up to 100 MHz.

Meant for running deep neural networks like RNNs and CNNs, Syntiant has optimized the NDP200, especially for power efficiency. Deep neural networks are necessary for computer vision applications.

Syntiant claims NDP200 performs vision processing at high inference accuracies. It does this while keeping the power consumption below 1 mW. Judging its performance, the chip could reach an inference acceleration of more than 6.4 GOP per second, while supporting more than 7 million parameters. This makes the NDP200 suitable for edge computing of larger networks.

Syntiant expects its chip will be suitable for battery-powered vision applications, such as security cameras and doorbells. In fact, the combination of the chip’s capability to run deep neural networks and power efficiency can allow it to take the next evolutionary step towards creating a better processor for computer vision applications.

Low-Power Circuit Timing using SPXOs

A wide range of electronic devices relies on circuit timing as a critical function. These include microcontrollers, Bluetooth, Ethernet, Wi-Fi, USB, and other interfaces. In addition, circuit timing is essential for consumer electronics, wearables, the Internet of Things (IoT), industrial control and automation, test and measuring equipment, medical devices, computing devices and peripherals, and more. Although designing crystal-controlled oscillators seems an easy process for providing system timing, there are numerous design requirements and parameters that designers must consider when matching a quartz crystal to an oscillator chip.

Among the several considerations are the negative resistance of the oscillator, its drive level, resonant mode, and the motional impedance of the crystal. When the designer is making the circuit layout, they must consider the parasitic capacitance of the PC board. They must also consider the on-chip integrated capacitance, and include a guard band around the crystal. Finally, the design must not only be compact, with a minimum number of components, and reliable. While the circuit must be capable of operating with a wide range of input voltages, consuming minimal power, it must also have a small root-mean-square jitter.

An optimal solution to the above is to use simply packaged crystal oscillators or SPXOs. Manufacturers optimize SPXOs for low RMS jitter and minimal power consumption. These devices can operate with any supply voltage ranging from 1.6 VDC to 3.6 VDC. With these continuous-voltage oscillators, designers can implement solutions requiring minimal effort while integrating them into digital systems.

In small, battery-powered, wireless devices, power consumption is always a very important consideration. That is why designers prefer to base such devices on the system on a chip or SoC processor that consumes very low power to support battery lives of several years. Moreover, device cost depends on the battery size, as the battery is easily the most expensive component in the device—minimizing the battery size is, therefore, an important factor in small wireless devices. For battery life consideration, one of the important parameters is the standby current, apart from the self-discharge current of the battery. Minimizing the current drawn by the clock oscillator is important, as this is greater than the standby current.

Designing low-power oscillators can be challenging. Designers are tempted to save energy by allowing the circuit to enter a disabled state for minimizing the standby current while starting the oscillator when needed. However, this is not an easy task as starting crystal oscillators quickly is not a simple and reliable task. Reliable start-up conditions require careful design efforts when designers attempt it across all environmental and operating conditions.

Most low-power wireless SoCs favor the Pierce oscillator configuration. The circuit has crystal and tow load capacitors. It uses an inverting amplifier that has an internal feedback resistor. With the amplifier feeding back its output to its input, the right conditions cause a negative resistance to start the oscillations going.

Quartz crystal oscillators can have jitters caused by power supply noise, improper load, improper termination conditions, the presence of integer harmonics of the signal frequency, circuit configurations, and amplifier noise. The designer must use several methods to minimize jitter.