Tag Archives: IC’s

What is Capacitance to Digital Converter Technology?

The healthcare industry has witnessed many advancements, innovations, and improvements in electronic technology in recent years. Healthcare equipment faced challenges like developing new treatment methods and diagnoses, home healthcare, remote monitoring, enhancing flexibility, improving quality and reliability, and improving ease of use.

A comprehensive portfolio of these technologies includes digital signal processing, MEMS, mixed-signal, and linear technologies that have helped to make a difference in healthcare instrumentation in areas such as patient monitoring and imaging. Another is the capacitance to digital converter technology that offers the use of highly sensitive capacitance sensing in healthcare applications. For instance, a capacitive touch sensor is a novel user input method that can be in the form of a slider bar, a push button, a scroll wheel, or other similar forms.

In a typical touch sensor layout, a printed circuit board may have a geometric area representing a sensor electrode. This area forms one plate of a virtual capacitor, while the user’s finger forms the other plate. For this system to work, the user must essentially be grounded with respect to the sensor electrode.

Analog Devices has designed their CapTouch controller family of ICs, the AD7147/ AD7148, to activate and interface with capacitance touch sensors. The controller ICs measure capacitance changes from single-electrode sensors by generating excitation signals to charge the plate of the capacitor. When another object, like the user’s finger, approaches the sensor, it creates a virtual capacitance, with the user acting as the second plate of the capacitor. A CDC or capacitance to digital converter in the ICs measures the change in capacitance.

The CDC can measure changes in the capacitance of the external sensors and uses this information to activate a sensor. The AD7147 has 13 capacitance sensor inputs, while the AD7148 has eight. Both have on-chip calibration logic for compensating for measurement changes due to temperature and humidity variations in the ambient environment, thereby ensuring no false alarms from such changes.

Both CDCs offer many operational modes, very flexible control features, and user-programmable conversion sequences. With these features, the CDCs are highly suitable for touch sensors of high resolution, acting as scroll wheels or slider bars, requiring minimum software support. Likewise, no software support is necessary for implementing button-sensor applications with on-chip digital logic.

The CDCs function by applying an excitation signal to one plate of the virtual capacitor, while measuring the charge stored in it. They also make the digital result available to the external host. The CDCs can differentiate four types of capacitance sensors by changing the way they apply the excitation.

By varying the values of these parameters, and/or observing the variations in their values, the CDC technology directly measures the capacitance values. The distance between the two electrodes affects the output of the CDCs in inverse proportions.

The family of Analog Device CDCs, the AD714x, AD715x, and AD774x, are suitable for applications involving a wide range of functions. These involve various input sensor types, input ranges, resolutions, and sample rates. Applications involve liquid level monitoring, sweat detection, respiratory rate measurement, blood pressure measurement, and more.

What are Ball Grid Arrays?

Initially, surface mount devices, especially ICs, came as perimeter-only packages, with pins for soldering placed along the edge of the device. As ICs became more complex, they needed more pins for external interfacing, which made the packages larger. Manufacturers soon realized there was a large unused real estate that lay just under the package. Therefore, they made the ball grid array (BGA) packaging, which, in place of pins, had solder balls aligned in a grid under the device. Soldering BGAs involves melting these solder balls onto pads on the PCB.

Using BGAs leaves a considerably larger area free on the PCB. Compared to mounting a package with pins on its perimeter, BGAs offer better thermal and electrical properties, and this has made the format popular, following the continued miniaturization of electronics.

Since their introduction, although their basic concept has remained the same, BGAs have changed in dimension and now come with far smaller pitches and smaller outlines. There are varieties as well, with some packages having connections only on the periphery and none at the center, while others have the connections distributed evenly across the bottom of the package.

For simpler BGAs, routing traces on the PCB is simple as the balls are placed well apart or there is space in the middle of the device. However, with increasing pin counts and decreasing pitches, routing between the pins becomes more difficult, resulting in increasing the layers of the board, thereby increasing the cost and reliability concerns.

As BGAs become increasingly more complex, designers have to depend on vias to connect the BGA with the rest of the circuitry on the PCB. Vias are small holes drilled through the multilayer PCB and plated with copper to provide connection between pads and traces on different layers. Some vias are through-hole types, meaning they start and end on the two extreme layers of the PCB, and may connect to other layers in between. Other vias can be blind types, starting from one of the outermost layers and ending on an internal layer, possibly connecting other layers in between. Blind vias are not visible on the PCB surface as they start and end at different internal layers, and may connect other internal layers as well. However, all the above require great precision while manufacturing, and are expensive processes.

Ordinarily, PCB designers prefer not to use vias on a pad, as during soldering, vias can wick solder from the pads leaving the joint in a dry and unsoldered state. However, with BGA pitches getting increasingly smaller, designers do not have much choice, but tenting is offering a way out. Tenting allows filling the via hole with an insulating material and covering the top with a layer of copper, thereby preventing wicking.

As the BGA pins lie in between the device body and the PCB, traditional soldering methods such as hand soldering and wave soldering are no longer useful, and assemblers rely on infrared heating or reflow ovens to solder BGAs to a PCB. This requires a pick-and-place machine placing the BGA package precisely on the pads and uniformly heating the area to form the actual connections.

Accurate Power Monitoring with LTC2992

Linear Technology Corporation, now a part of Analog Devices, Inc., has recently placed on the market a power monitoring IC, LTC2992, which offers a wide-range, dual monitoring system for current, voltage, and power for 0-100 VDC rails. The IC is self-contained and does not need additional circuitry for functioning.

Users get a variety of options for operating the LTC2992. For instance, they can derive power from a 3-100 VDC monitored supply, or from a 2.7-100 VDC secondary supply, or from the shunt regulator on-board. Therefore, when monitoring the 0-100 VDC rail, the designer does not have to provide a separate buck regulator, a shunt regulator, or an inefficient resistive divider.

Within the LTC2992 are a multiplier and three Analog to Digital Converters (ADCs) of the delta-sigma type. Two of the ADCs provide measurements for current in each supply, while the third ADC measures voltage in 8- or 12-bit resolution and power in 24-bit resolution. The wide operating range of the LTC2992 makes it an ideal IC for several applications such as blade servers, advanced mezzanine cards, and 48 V telecom equipment.

Users with equipment using negative supply or supply greater than 100 VDC can make use of the onboard shunt regulator. The LTC2992 has registers that one can access with the I2C bus, and it uses these registers to store the measured values. It can measure current and voltage on-demand or continuously, using these to calculate the power, and stores this information along with maximum and minimum values in the registers.

The LTC2992 has four GPIO pins, which the user can configure as ADC inputs for measuring neighboring auxiliary voltages. Over its entire temperature range, the LTC2992 takes measurements with only ±0.3% of the Total Unadjusted Error (TUE). For any parameter going beyond the thresholds programmed by the user, the LTC2992 raises an alert flag in the specified register and on the specified pin. This is according to the alert response protocol of the SMBus.

The I2C bus on the LTC2992 operates at 400 kHz and features nine device addresses, a reset timer for a stuck bus, and a split SDA pin for simplifying the opto-isolation for the I2C. Another version of the IC, the LTC2992-1 offers users an inverted data output pin for the I2C. This makes it easy for the users to interface the IC where the opto-isolator has an inverting configuration.

The ICs, LTC2992 and LTC2992-1, are both available in automotive, industrial, and commercial versions. Their operating temperature ranges are -40°C to 125°C for automotive, -40°C to 85°C for industrial, and 0°C to 70°C for commercial applications. Linear Technology Corporation makes both versions of the IC in packages of 16-lead MSOP and 16-lead 4 x 3 mm DFN, and both versions are RoHS-compliant.

Most electronic applications require monitoring of current, voltage, and power at board level. Knowing the key system parameters provides valuable feedback, allowing users to monitor the health of their systems and make intelligent decisions. They help in determining whether a system is operating properly, efficiently, or even dangerously. Users can choose for various types of monitoring ICs, ranging from hot-swap dedicated power ICs to temperature monitors.

Why Do ICs Need Bypass Capacitors?

Any electronic design engineer will vouch for the necessity of supplementing integrated circuits on their PCB with bypass capacitors, although they may not understand the reason to do so very well. As a rule of thumb, engineers provide every IC with a 0.1µF ceramic capacitor next to its power pins in each circuit board they design. Along with proper PCB layout techniques, adding a bypass capacitor improves circuit performance and maximizes the efficacy of the ICs.

The trouble lies with transition currents. Circuits handling digital signals produce rapid transitions when their signals switch states. When digital circuits output a high state, the signal voltage is very close to the supply voltage. When they output a low state, the signal voltage reaches very near the ground voltage. When transiting from a low to high or a high to low, the voltage swing from supply to ground or from ground to supply, causes a transient current to be drawn from the supply.

Usually, power to an electronic circuit on a PCB is fed at a single point and traces on the PCB carry this power to each IC. Traces on the PCB have their own parasitic inductance, which, when coupled with the source impedance of the power supply, react to transient currents by creating voltage transients.

The trouble aggravates when ICs have to drive low-resistance or high-capacitance loads. The low-resistance demands high currents when the digital state changes from low to high. Again, when the digital state changes from high to low, there is a demand for the load current to reduce suddenly. However, according to Lenz’s Law, an induced current will flow such as to oppose the change that produced it.

The net effect of transient currents and the parasitic inductance of PCB traces and wires are to create high-magnitude voltage transients, ringing or severe oscillations in the power lines. This can lead to suboptimal circuit performance or even to system failure. Engineers at Texas Instruments have demonstrated an improperly bypassed line driver IC switching at 33MHz can induce ringing amplitude of the order of 2V peak-to-peak on a 5V power rail.

Placing a 0.1µF ceramic capacitor close to the IC power pins improves the situation, because capacitors store charge. Placing the bypass capacitor close to the IC allows low resistance and series inductance. The bypass capacitor is therefore in a better situation to supply or absorb the transients on the PCB traces, which have a comparatively larger resistance and series inductance.

Although engineers refer to such components as both bypass and decoupling capacitors, there is a subtle distinction between the two terms. Decoupling refers to the amount by which one part of the circuit influences another. Bypassing provides a low-impedance path allowing noise to pass by an IC on its way to ground. A capacitor, placed close to the IC supply pins, accomplishes both decoupling and bypassing. However, a decoupling capacitor has an additional task. It blocks the DC component of a signal and prevents it from traveling through to the next part of the circuit, while allowing the AC component little or no resistance at all.

How Does Switching Affect Semiconductors?

Even though ICs rule the world of electronics, the transistor does all the work. Within each IC are millions upon millions of transistors perpetually switching on and off so that the IC can carry out its intended functions. Even if one of the multitudes of transistors were to stop switching, the IC could lose part or all of its functionality.

Circuits handling digital signals most often use transistors to switch from a high state to a low state and vice versa. It is usual to call a circuit point as being in a high state if the voltage at that point is close to the supply voltage. If the circuit point is closer to the ground or zero voltage, we generally call it as being at a low state. The time taken for the transistor to switch from a high to a low state or vice versa is its switching rate. While the transistor does not expend much energy when at either the low or the high state, the same cannot be said for the time when it is actually switching.

Under ideal conditions, a transistor should switch instantaneously. That means the transistor should take zero seconds to change its state. However, ideal conditions do not happen in reality and the transistor takes a finite time, however small, to actually switch over.

Transistors are made of semiconductor material and each junction has a finite capacitance and resistance. Junction capacitances store energy and the combination of resistance and capacitance acts to slow down switching – the capacitance must fill up or empty itself before the transistor can flip. The rate at which the capacitance fills up or empties itself depends on the junction resistance.

The situation gets worse as the switching frequency goes up. As the transistor is driven to toggle faster and faster, the junction capacitance may not get enough time to discharge or charge up fully. That defines the maximum switching rate the transistor can achieve.

Semiconductor manufacturers use various methods to reduce junction capacitances and resistances to induce these special semiconductors switch faster. Although modern semiconductors (transistors and diodes) are capable of switching at MHz or GHz scales, the cumulative effect of the tiny switching losses add up to increase the junction temperature.

Power is the product of voltage and current. When a semiconductor is in a high state, although the voltage is high, the current is negligible and consequently, the power drawn from the supply is negligible. When the semiconductor is a low state, its voltage is close to the ground level and the product of current and voltage is again negligible.

However, during switching, when the voltage is somewhere in-between the supply and ground levels, the current drawn also increases. That makes the product of voltage and current have a significant value and the semiconductor generates heat because of the power consumption. With higher frequencies, this happens more frequently and the heat accumulates to produce higher junction temperature.

If the natural process of heat dissipation can remove the accumulated heat, the semiconductor soon reaches a steady temperature. Else, heatsinks and or forced cooling methods are necessary to remove the heat accumulated.

Demystifying the A/D and D/A Converters

Analog and Digital Signals

Analog signals represent a physical parameter in the form of a continuous signal. In contrast, digital signals are discrete time signals formed by digital modulation. Most natural signals, like human voice and other sounds are analog in nature. Traditionally, communication systems were based on analog systems.

As demand for systems capable of carrying more information over longer distances kept soaring, the drawbacks of analog communication systems became increasingly evident. Efforts to improve the performance and throughput of systems saw the evolution of digital systems, which far surpasses the performance of analog systems, and offer features that were considered impossible earlier. Some major advantages of digital systems over analog are:

• Optical fibers can transmit digital signals and have virtually infinite information bearing capacity
• Combining multiple input signals over same channel is possible by multiplexing
• Digital signals can be encrypted and hence are more secure
• Better noise immunity leads to superior performance due to regeneration
• Much higher flexibility and ease of configuration

On the other hand, disadvantages include:

• Higher bandwidth required to transmit the same information
• Accurate synchronization required between transmitter and receiver for error free communication

Primary signals like human voice, natural sounds and pictures, etc., are all inherently analog. However, most signal processing and transmission systems are progressively becoming digital. Therefore, there is an obvious need for conversion of analog signals to digital. This facilitates processing and transmission, and reverse transition from digital to analog, since the digital signals will not be intelligible to human receivers or gadgets like a pen recorder. This need led to the evolution of Analog to Digital (A/D) Converters for encoding at the transmitting end and Digital to Analog (D/A) Converters at the receiving end for decoding.

Principle of Working of A/D and D/A Converters

An A/D converter senses the analog input signal at regular intervals and generates a corresponding binary bit stream as a combination of 0’s and 1’s. This data stream is then processed by the digital system until it is ready to be regenerated at the receiver’s location. The sampling rate has to be at least twice the highest frequency of the input signal so that the received signal is a near perfect replica of the input.

In contrast, a D/A Converter receives the bit stream and regenerates the signal by plotting the sampled values to obtain the input signal at the receiving end. The simplest way to achieve this is by using a variable resistor network, which converts each digital level into an equivalent binary weighted voltage (or current). However, if the recipient is a computer or other device capable of handling a digital signal directly, processing by D/A Converters is not necessary.

Two of the most important parameters of A/D and D/A Converters are Accuracy and Resolution. Accuracy reflects how closely the actual output signal resembles the theoretical output voltage. Resolution is the smallest increment in the input signal the system can sense and respond to. Higher resolution requires more bits and is more complicated and expensive, apart from being slower.

Microchips to be imbedded in pills?

Yes, it’s true. Proteus Biomedical has announced that they will be launching a innovative product that imbeds microchips in pills so that patients can be monitored by their health care professionals and even their families.

The purpose of the monitoring is to be sure that patients are taking their medications properly and on time and to also monitor a range of additional patient information including respiration rate, heart rate, temperature, sleep patterns and physical activity. It is estimated that up to 50% of all patients take their medication improperly so this will assist health care professionals and family member with the patient’s drug regimen.

The sensors are about the size of a grain of sand. The sensor-enabled tablets are called Helius. The Helius can be taken with pills or incorporated into medications by the drug manufacturers. Once ingested, the sensors are activated by stomach acid. Each sensor contains a very small amount of copper and magnesium which react with stomach acid to create the power necessary to generate a digital signal. Through an adhesive patch on the skin, the digital signal is read and and the data transmitted through the patient’s cell phone.

Don’t look for the microchipped pill just yet. Proteus Biomedical will be introducing their new product in the UK first.

Available Methods of Marking Semiconductors

Semiconductor Markings – Available Methods

Traditionally, most components have two or three lines of identifying marks plus a company logo. Over time, the manufacturer codes have become more involved to incorporate a component’s identification plus the complete history of the process. Early on, it was the military applications that required very specific markings and identification processes. Current package markings are a by-product of those military requirements.

When a semiconductor is clearly identified, there is less room for error in the production process. Reducing errors when a component is in use for production saves time. There is also less product waste and the production process becomes more streamlined.

As the size of electronic components has decreased, the available space that manufacturers have to mark each piece has also decreased. The technology required to complete this task has become increasingly more complex.

The chief reason for the more complex codes stems from the demands of the end users. They need to have complete traceability of the product; from the history of the production cycle including the date and location of manufacture to the exact lot code. Possession of this information is critical to the end user in the event of a recall or defective components.

There are four primary methods to marking components in current use. Use of the various methods depend on the size, the type and the environment of the component production.

The methods are:
-Ink marking
-Electrolytic marking
-Pad printing
-Laser marking

In ink marking, inkjet printers are used. The technology is called ‘drop-on-demand’ which means that the flow of ink is controlled to create a pattern of ink droplets to form an image marking.

Electrolytic marking employs low voltage electric current with a stencil. The top layer of the package is etched by electricity flowing from the marking head, assisted by an electrolyte chemical. The process takes approximately 2-3 seconds to complete.

Pad printing is the most traditional of all the processes. A steel plate is etched with the image of the imprint. The ink is transferred to the plate which then is applied with pressure to the surface of the electronic component.

Laser marking is the most recent development in the marking process. It provides the greatest flexibility in the size, timing and complexity of the markings. The laser process is also the fastest method to mark electronic components; it is not uncommon for this process to print up to 300 characters per second. An additional benefit of using laser printing is the ability to produce a clean mark on many irregular surfaces.

No matter which method has been used to mark the semiconductors you use, you can be sure that much thought has been put into the decision.

Op Amps – Then and Now

Op Amps – Then and Now

Op amp is the commonly used name for operational amplifiers, which are widely used electronic components. Op amps are often seen on many surface equipment designs and logging tools.

The name ‘operational amplifier’ comes from the use of such high gain amps in performing mathematical operations for analog computer operations and is said to have been coined in 1947. A lot of study was done in the field and the initial operational amplifiers, based on vacuum tubes, were a result of the research done in Bell labs. By 1960’s, vacuum tube op amps had given way to solid state devices and hybrid operational amplifiers were entering the scene.

The first IC operational amplifier was developed in 1963 by Bob Widlar and was called Fairchild µA702. It was not a success because of a number of bugs. But Widlar’s next design, which was the µA709, was hailed as milestone in design. A number of designs followed including the very popular µA741. A number of precision op amps like OP7, OP27 and OP37 are commonly used in logging electronics.

In the initial days, these electronic components were based on NPN bipolar process and because of the slow PNP transistors of the time; the speed of the amps was limited. The LM118/218/318 model tried to solve the problem but did not meet with much success. The only fast IC op amps were the ones owned by Harris, the HA2500 as well as the HA2600, and were quite popular despite their high cost.

FET input operational amplifiers though highly advantageous in downhole tool applications, did not enter the scene due to engineering problems. However with the introduction of the ion implantation process in 1974, their manufacture became possible and the LF155/156/157 series was introduced by National Semiconductor, and OP15, OP16, and OP17 by PMI. The TL06x, TL07x, and TL08x models introduced by Texas Instruments (TI) in 1978 went on to become industry standards.

The CA3130 employing a P-channel MOS input with a CMOS output, set the stage for CA3140 having a MOSFET input and a bipolar output which caught the eye of many logging tool companies. This model has many advantages including good bandwidth and military temperature range, and continues to be used and manufactured even now.