• Differential Data Transfer: What's the Difference?

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    The main function of an isolator is to transmit some form of information through an electrical isolation barrier while blocking current flow. The isolator is made of insulating material that blocks current flow, and there are coupling elements across the isolation barrier. Information is usually encoded by the coupling element before being transmitted through the isolation barrier.

    Analog Devices' iCoupler® digital isolators use chip-scale microtransformers as coupling elements to transmit data across high-quality polyimide isolation barriers. There are two main data transfer methods used in iCoupler isolators: single-ended and differential. When selecting a data transfer mechanism, engineering design trade-offs are required to optimize the desired end product characteristics.

    In single-ended data transmission, we use a transformer with one end of the primary winding connected to the ground. Logic transitions in the input signal are encoded as pulses, always positive with respect to ground, on the transmitter chip. This is also known as "one pulse, two pulses" because rising edges are encoded as two consecutive pulses while falling edges are represented as a single pulse (see the top of Figure 1). The receiver on the other side of the isolation barrier receives the signal and determines whether one or two pulses were sent; it will then reconstruct the output accordingly.

    Differential data transmission uses a true differential transformer. In this case, a single pulse is always sent when the input edge is detected, but the polarity of the pulse determines whether the transition is rising or falling (bottom of Figure 1). The receiver is a true differential structure and updates the output according to the pulse polarity.

    One of the main advantages of the single-ended approach is lower power consumption at low data rates. This is because differential receivers require more DC bias current than CMOS Schmitt triggers used in single-ended receivers. However, the differential method consumes less power at higher throughput rates for two reasons: drive level and number of pulses. The drive level of the transformer can be reduced because the receiver only needs to determine the polarity, not whether there is a single pulse or two pulses. Single-ended systems require an average of 1.5 pulses per edge, while differential transmission requires 1 pulse per edge (a 33% reduction).

    Reduced drive levels and fewer pulses can also reduce RF radiation. The radiation is caused by current pulses in the power supply causing radiation from the printed circuit board structure. With fewer pulses and lower energy per pulse, significantly less RF radiation is generated.

    Differential transmission has two other advantages over single-ended systems: propagation delay and noise immunity. In the single-ended method, a specific timing relationship must exist when creating a single pulse or two pulses, and the receiver must analyze the pulses within a specific time window. These requirements place constraints on encoding and decoding, and ultimately, the propagation delay through the device. This in turn limits the overall throughput that the device can achieve. The differential method is less restrictive because it always uses a single pulse, resulting in lower propagation delay and higher throughput.

    Differential receivers can reliably detect the differential signal sent by the transmitter, and also reject unwanted common-mode noise ubiquitous in isolated systems, resulting in significantly improved common-mode transient immunity (CMTI). Differential receivers are also less susceptible to power supply noise and therefore have higher noise immunity. The LEDs used in optocouplers are single-ended in nature, which is one reason why optocouplers typically have poor CMTI performance. Differential data transmission enables iCoupler digital isolators to significantly improve performance over optocouplers.

    A data transfer method is also an option for...

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  • How much do you know about the factors that affect the current carrying capacity of cables?

    01/12/2022 at 07:12 0 comments

    The position of wires in the industrial control process is very important, and the use of frequency converters, industrial computers, sensors, and other equipment is indispensable for cable lines. The flow rate refers to the amount of current passed by a cable line when transmitting electrical energy. Under thermal stability conditions, the cable current carrying capacity when the cable conductor reaches the long-term allowable working temperature is called the long-term allowable current carrying capacity of the cable.

    In practical projects, different cable types can be selected according to the long-term allowable current carrying capacity of the cables under different environments and conditions, and the required number of cables and laying forms can be determined. Therefore, it is of great significance to calculate the long-term allowable current carrying capacity of the cable.

    Let's first talk about the internal factors that will affect the current carrying capacity of the wire in use:

    1. Core area

    That is to say, the "wire diameter" we often say, is not the cross-sectional area of the whole wire that determines the current carrying capacity, but the cross-sectional area of the conductor inside the wire. The thicker the wire, the greater the current-carrying capacity. The thickness of the conductor is approximately proportional to the magnitude of the current. It is the diameter that is proportional to the current, not the cross-sectional area. For cables of the same material, the thicker the cable, the stronger its current-carrying capacity. Therefore, the thicker the cable, the better its current-carrying properties. Under the same current, the heat dissipation performance is better. Choose thin cables, if the current is too large, there will be dangers of overheating, melting, burning, etc.

    2. Material conductivity

    It depends on the conductor material, such as ordinary copper wire and aluminum wire, the conductivity of copper material is at least 30% higher than that of aluminum. In addition to the substance of the raw material, it also depends on the purity of the raw material. Taking copper as an example, the conductivity of high-purity copper is much higher than that of secondary copper.

    3. Thermal conductivity of the insulating layer

    In addition to preventing electric shock, the role of the insulating layer also has the same important role as the Anti-electric shock flame retardant. The better the thermal conductivity of the thermal insulation material, the better the flame retardancy. Therefore, the quality of the insulating material determines the current carrying capacity of the wire from another aspect.

    External factors that affect wire current carrying capacity:

    In addition to some external factors that will reduce the current carrying capacity of the cable under certain circumstances, there are also internal factors that can determine the current carrying capacity of the wire, which are mainly determined by the following three points:

    1. length

    The longer the cable, the lower the load-carrying capacity. The difference between the carrying capacity of one kilometer and the carrying capacity of 10,000 meters is not an order of magnitude.

    2. temperature

    The higher the temperature, the lower the current-carrying capacity of the wire. This is the most common problem and the main reason why cables used in buildings need to be thicker than plug-in cables. In many cases, the ambient temperature is uncontrollable, and the ventilation effect, sunlight, cable density, etc. will affect the ambient temperature, thereby affecting the current carrying capacity of the cable.

    3. Cable density

    If multiple cables are too close together, the charge will be concentrated somewhere in the conductors instead of being evenly distributed, which will greatly reduce the cable's current-carrying capacity. Reasonably arrange the cable spacing and increase the cable spacing.

    Summarized by Easybom.

  • What is a fingerprint sensor?

    01/08/2022 at 08:49 0 comments

    Fingerprint sensoris the key device to realize automatic fingerprint collection. Fingerprint sensors are divided into optical fingerprint sensors, semiconductor capacitive sensors, semiconductor thermal sensors, semiconductor pressure-sensitive sensors, ultrasonic sensors, and radio frequency RF sensors according to the sensing principle, that is, the principle and technology of fingerprint imaging. The manufacturing technology of fingerprint sensor is a high-tech with strong comprehensiveness, high technical complexity and difficult manufacturing process.

    Because of its complex manufacturing process and many sensing units per unit area, semiconductor fingerprint sensors include high-end IC design technology, large-scale integrated circuit manufacturing technology, IC chip packaging technology, etc., so almost all semiconductor fingerprint sensors are made by countries with developed IC technology or regions, such as the United States, Europe, Taiwan and other places designed and manufactured. More than 10,000 semiconductor sensing units are integrated on the surface of a wafer less than 0.5 square centimeters. It also includes automatic gain circuit and logic control chip, as well as serial, parallel, USB and other interface circuits. The semiconductor fingerprint sensor has high sensitivity and a resolution of 500dpi or above. Its function has broken through the single sensing ability, and with the cooperation of software, it can be used as an omnidirectional navigator. Semiconductor fingerprint sensors are developing towards miniaturization. Before 2004, the 1 square centimeter square was mainly used, and most of them were sliding SWIPE chips. The world's smallest sliding acquisition chip is only 12x5 mm, which is the 1610 recently launched by Authentec. Prisms exist in optical sensors, which are relatively large, generally several times or even 10 times the size of semiconductors, which limits their application in small devices. There is no volume limit when using on large devices such as attendance machines and access control, but when using it on U disks, mobile hard disks, and handheld devices, the volume becomes the biggest obstacle, so optical fingerprint sensors also appear sliding.

    Applications of Fingerprint Sensors
    The fast-changing fingerprint recognition technology market has penetrated deep into the consumer segment - fingerprint sensor shipments will grow at a CAGR of 18% and are expected to reach a market size of $4.7 billion in 2022.

    Following the acquisition of fingerprint sensor company Authentec, Apple released the iPhone 5s in 2013, thus driving the mass adoption of fingerprint sensors. In the years since, fingerprint sensor shipments in the consumer market have shown incredible growth. At first, fingerprint sensors were used for phone unlocking and information protection. Now, however, fingerprint sensors are increasingly being used for security functions such as online identification and mobile payments.

    Shipments of fingerprint sensors used in smartphones increased from 23 million in 2013 to 689 million in 2016. It can be seen that from 2013 to 2016, the compound annual growth rate of fingerprint sensor shipments for mobile phone applications was as high as 210%! Growth in this segment is expected to be “rational” between 2016 and 2022, with a CAGR of around 18%.

    Fingerprint recognition is becoming a standard feature in every smartphone and adding a lot of practical value. However, the rapid growth in shipments is accompanied by strong cost pressures, which is a realistic portrayal of what has happened to fingerprint sensors in the past three years. The average cost of a fingerprint sensor has dropped from about $5 in 2013 to about $3 in 2016, and low-end fingerprint sensors are even more affordable. Still, cost pressures have not gone away. Current technologies are maturing and threatened by new technologies. New technologies need to gain momentum through "lower costs". For example, 3D ultrasonic...

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