App note: Replacing mechanical potentiometers with digital potentiometers

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Another application note from Analog Devices this time about the superiority of digital over mechanical potentionmenters. Link here (PDF)

Potentiometers have been widely used since the early days of electronic circuits, providing a simple way to calibrate a system, adjusting offset voltage or gain in an amplifier, tuning filters, controlling screen brightness, among other uses. Due to their physical construction, mechanical potentiometers have some limitations inherent to their nature, such as size, mechanical wear, wiper contamination, resistance drift, sensitivity to vibration, humidity, and layout inflexibility.

Digital potentiometers are designed to overcome all these problems, offering increased reliability and higher accuracy with smaller voltages glitches. The mechanical potentiometer has now been relegated to environments where the digital potentiometer cannot be a suitable replacement, such as high temperature environments or in high power applications.

Comparing both technologies is the simplest way to discern which is the optimal solution for your system.

App note: Precision signal conditioning for high resolution industrial applications

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App note from Analog Devices on robust precision signal conditioning. Link here (PDF)

Industrial measurement and control systems often need to interface to sensors while operating in noisy environments. Because sensors typically generate very small electrical signals, extracting their output from the noise can be challenging. Applying signal conditioning techniques, such as amplification and filtering, can aid in the extraction of the signal because these techniques increase the sensitivity of the system. The signal can then be scaled and shifted to take full advantage of high performance ADCs.

Controlling an HMC624LP4E RF attenuator using Arduino

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Kerry Wong writes:

For simplicity, I used a single rotary encoder for controlling the attenuation. In order to prevent accidentally changing the set attenuation value, I used the built-in switch of the rotary encoder as the lock/adjust control. The idea is that the attenuation value can only be adjusted when the switch is in the “adjust” state and the attenuation value is set once the switch changes from adjust to the lock state. When the switch is in the “locked” state, adjusting the rotary encoder has no effect on the digital attenuator. The current attenuation value is displayed on a 1×16 LCD. For more details, you can find the Arduino code listing towards the end of this post along with a video demonstrating this control interface.

More details on Kerry Wong’s blog.

Check out the video after the break.

App note: Capacitor selection guidelines on LDOs

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They are different kind of capacitors, selection for one capacitor varies depending on application. A good read app note from Analog Devices. Link here (PDF)

Capacitors are underrated. They do not have transistor counts in the billions nor do they use the latest submicron fabrication technology. In the minds of many engineers, a capacitor is simply two conductors separated by a dielectric. In short, they are one of the lowliest electronic components.

It is common for engineers to add a few capacitors to solve noise problems. This is because capacitors are widely seen by engineers as a panacea for solving noise related issues. Other than the capacitance and voltage rating, little thought is given to any other parameter. However, like all electronic components, capacitors are not perfect and possess parasitic resistance, inductance, capacitance variation over temperature and voltage bias, and other nonideal properties.

These factors must be considered when selecting a capacitor for many bypassing applications or where the actual value of the capacitor is important. Choosing the wrong capacitor can lead to circuit instability, excessive noise or power dissipation, shortened product life, or unpredictable circuit behavior.

App note: DAC ICs: How many bits is enough?

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A very old application notes from Analog Devices that tells about Nyquist Theorem, sampling rate and quantization used on DACs. Link here (PDF)

At the heart of every digital audio playback system lies the single-most critical component for high-fidelity audio: the digital-to-analog converter (DAC). These converters handle the delicate task of translating the 16-bit binary words encoded on the disc or tape into corresponding analog signals worthy of amplification and, ultimately, of the human ear.

App note: iCoupler® Isolation in CAN bus applications

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Application note from Analog Devices on CAN bus system isolation. Link here (PDF)

The intention of this application note is to give the user a brief overview of the CAN bus protocol, focusing on the system physical layer, as well as an understanding of why isolation is so important to the system. This application note also details how to implement isolation in a CAN bus system using Analog Devices’ iCoupler products.

App note: Fast Rail-to-Rail operational amplifiers ease design constraints in low voltage high speed systems

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Migration to lower rail voltages considerations on operational amplifier designs an Application note from Analog Devices. Link here (PDF)

Movement towards lower power supply voltages is driven by the demand that systems consume less and less power coupled with the desire to reduce the number of power supply voltages in the system. Lowering power supply voltages and reducing the number of supplies has obvious advantages. One such advantage is to lower system power consumption. This has the additional benefit of saving space. Lowering overall power consumption has a residual benefit in that there may no longer be a need for cooling fans in the system.

However, as the traditional system power supply voltages of ±15 V and ±12 V give way to lower bipolar supplies of ±5 V and single supplies of +5 V and +3.3 V, it is necessary for circuit designers to understand that designing in this new environment is not simply a matter of finding components that are specified to operate at lower voltages. Not all design principles used in the past can be directly translated to a lower voltage environment.

Reducing the power supply voltage to a typical op amp has a number of effects. Obviously, the signal swings both at the input and output are reduced. The required headroom between signal and rail (typically 1 V to 2 V in conventional amplifiers), which is of lesser importance with power supplies of ±15 V, now drastically reduces the usable signal range. While this reduction does not normally increase noise levels in the system, signal-to noise ratios will be degraded. Because the designer can no longer use techniques such as increasing power supply voltages and signal swings in order to “swamp” noise levels, greater attention must be paid to noise levels in the system.

App note: Resolution enhancements of digital potentiometers with multiple devices

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An old application note from Analog Devices about configuring multiple digital potentiometers to improve resolution, accuracy and programming complexity might add-up to the mix though. Link here (PDF)

Digital potentiometers usually come with standard resistance values of 10k, 100k, and 1MW at a given number of adjustable steps. If an application requires a resistance range that falls between these values, users will most likely apply a part with a resistance larger than needed scarifying resolution. Fortunately, users can parallel, stack, or cascade multiple digital potentiometers to optimize the resolution for a given application. In this article, we will share some of the ideas that may solve the challenge.

App note: Implementing an I2C reset

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Interesting app note from Analog Devices when an I2C communication is broken under some circumstances. Link here (PDF)

The I2C bus is a high integrity, robust serial bus used for control purposes in many systems. The primary components that make up a system are at least one master and one slave. Under normal conditions, everything works fine; however, it is the abnormal conditions that generate problems. Two questions present themselves when a problem arises: Is the problem device or system related, or some combination of both? What, if anything, can be done about it?

Hard device failures are relatively easy to isolate. Perhaps a function does not work, proper power cycling does not resolve the issue, pins are stuck high or low, and so on. System related problems sometimes disguise themselves as device failures, or worse, are intermittent. It is the latter area that this application note examines because it represents the majority of bus fault conditions.

Frequently the master, which is usually a microcontroller or a gate array, will be interrupted in the middle of its communication with an I2C slave and, upon return, find a stuck bus. Initially this looks like a device problem, but it is not. The slave is still waiting to send the remainder of the data requested by the master. The problem is that the master has forgotten where it was when it was interrupted or reset.

App note: Environmental compensation on the AD7142: The effects of temperature and humidity on capacitance sensors

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An old but useful application from Analog Devices about things that can affect touch/capacitance sensors. Link here (PDF)

Capacitance sensing has the potential to replace current user input mechanisms in consumer devices. Products as diverse as cell phones, digital cameras, MP3 players, and other portable media players are all suitable for implementing capacitance sensing.

Capacitance sensing has many benefits. It gives the user an interface with greater sensitivity and control. Capacitance sensors are easy to manufacture and reliable, and have advantages over current mechanical interfaces. However, all types of capacitance sensors are affected by capacitance changes in the surrounding environment. Changes in humidity or temperature can interfere with the operation of the sensors, in some cases stopping the sensor from working altogether.