Index

Electronics basics

    Basics

      Cooling

      Heatsinks are the most basic form of cooling next to simple surface convection in today's electronics devices. If you look inside the average PC, you'll probably find two or three heatsinks: on CPUs, video cards, and even the chipset of a motherboard. Heat sinks are also seen on power electronics devices like power supplies, power amplifiers, light dimmers and electronics power switching components (like SSRs).

      Typically heatsinks appear as nothing fancy: hunks of aluminum with a large number of protrusions. While there are different ways of manufacturing heatsinks, and different philosophies in the way they are shaped, the idea of all of them is the same: increase surface area to increase heat dissipation.

      Not all heat sinks are created equal. The most important factor in a heatsink is, naturally, its ability to dissipate the largest amount of heat in the shortest amount of time. How good the heatsink is in this is typically indicated by how much one watt of power will heat it (C/W rating). The lower the C/W rating, the better the heat sink is at dissipating the heat, given proper ventilation and ambient temperature. Commercially made heat sinks typically have this number listed in their data sheet. This ability to transfer heat away from the component depends on a number of factors. First is material. The vast majority of heatsinks are made out of aluminum. Aluminum is an excellent conductor of heat, and relatively cheap. Roughly speaking, conduction can be understood as the transfer of molecular kinetic energy between solids. Copper is indeed a better conductor than aluminum, but because of it's higher price it is not common.

      The second factor in heatsink effectiveness is, as mentioned above, surface area. The protrusions function to make the exposed surface area many times greater than if the same amount of material was in a solid block. The greater the surface area exposed to the air, the greater the dissipation of heat for a given quantity of metal. The temperature gets out of heatsink through convection and radiation. Convection transfers kinetic energy from solid object into the air. Most solutions now use fans to force larger quantities of air over the surface of a heatsink.

      When heatsink is hot, it also radiates some of the hat as heat radiation, but on low temperatures the heatsinks normally are (typically below 100 degrees celsius) the radiation of heat is quite low. It is true, that the color of heat sink has some effect on radiation, but different color heatsinks are so similar once they're closed up inside your machine that they can be safely ignored.

      Heatsinks are approximately equivalent, in heat dissipation, to a sheet of aluminum 1/8" thick by the dimensions shown below:

      • 12" X 12" = approximately 2.1 degrees C per watt thermal rise (2.1 C/W)
      • 15" X 15" = approximately 1.5 degrees C per watt thermal rise (1.5 C/W)
      • 18" X 18" = approximately 1.0 degrees C per watt thermal rise (1.0 C/W)
      In comparison, twice the amount of steel and four times the amount of stainless steel would be needed to achieve the same effect. Remember that the heatsink removes the heat from the electronic component that needs to be cooled and transfers that heat to the air in the electrical enclosure. In turn, this air must circulate and transfer its heat to the outside ambient. Providing vents and/or forced ventilation is a good way to accomplish this. It is a good idea to have at least one inch below them, so air can enter the finned heat sink area (if you have less free area, the heatsink is less efficient, meaning higher C/W rating). Heatsinks should always have empty space above them so the warm air can exit the heat sink area.

      The heat must be transfered from the electronics component to a heat sink in some way, typically the component is mouted on heatsink (regulators, transistors, thyristors etc.) or heatsink is mounted on the top of the component (typical ICs). The best thermal contact is metal to metal (when the whole metal area touches each other and there is thus no insulating air gaps between metal). The best way of acheiving this is by "lapping" the contact area's together with a fine abrasive. Once your have done this the application of a minute amount of thermal grease improves conductivity by less than 0.5%. We also discovered that applying more than a fine film or grease significantly decreased the conductivity (10% or more). Due to the machining process, just about every heat sink will have a rough surface. To the naked eye it may look flat or even feel smooth, but there are microscopic groves in the surface. These groves will trap air between the heat sink and the CPU or other heat generating electronics component, and cause a poor transfer of heat. Thermal compound (Artic Silver, Nanotherm, etc.) is used to fill these groves and help transfer the heat from the CPU or other electronics part to the heat sink.

      Lots of OEM or low end cooling setups use either a thermal interface pad (TIM) or that white goop (slicon based paste) you get at radio shack. The fact is that neither of those does an excellent job of transferring heat from the processor or other component to the heatsink, they work ok. The problem with current commercial pastes is that they have focused on the thermal conductivity of the material, and not on the fundamental principle of a thermal paste, which is gap filling. Silicone based 'goop' from is fairly thermally conductive, but the size of the particles and the terrible spreadability can cause it to be more of an insulator than a conductor. On the other hand, using something entirely liquid such as mineral oil doesn't cool well either because it isn't conductive enough. Even the very best silver-filled grease is 1/32nd the thermal conductivity of Aluminum. An Indium gasket is probably the best you can do, and is is still very much worse temperature conductor than aluminium. Paste isn't meant to be used like car body filler. The key is to find something with the right balance of conductivity and spreadability. Try to eliminate the gap. Correct application is critical to the effectiveness of thermal goop. The idea is to get a very thin, uncontaminated layer of the stuff between the chip and the heatsink. Any kind of oil, scratches, dust, etc. can cause efficiency to drop.

      ASICs

      High speed digital design

      When designing high speed digital systems, you need to understand much more than just bits. According to the classical view, the days when you could ignore signal integrity issued ended when bus-clock rates passed approximately 50 MHz. At that point, give or take a few megahertz, when you designed buses or interconnects, you had to start taking terminations seriously and stop thinking of reflections as just a little overshoot and ringing on waveform edges at state changes. Because of fundamentally analog SI (signal-integrity) issues that accompany today's higher data / signal rates, digital electronics is now as much analog as it is digital. There are only two kinds of electronics engineers working on this field: those who have had SI problems and those who will. Ideally, all high-speed-logic designs should include tightly coupled bypass capacitors for each IC, and all multilayer pc boards should have power and ground distribution planes. Unfortunately, poor design practices still exist, such as using just one bypass capacitor at the power entrance to a logic board and routing power and ground to the ICs from opposite sides of the board. This faulty distribution scheme creates large spikes on the logic supply voltage and produces significant electromagnetic fields around the board and unstable power for the ICs in the board. High system speeds are making clock design a critical problem: Clock signals distributed within a printed-circuit board andaround a system must be clean, stable, synchronized, and have as near toa 50:50 duty cycle as possible. Historically, designing high-speed signals into small, low-pin-count packages required little attention to impedance matching. Nowadays things have changed. As current and future generations of high-speed devices move into larger and denser packages with longer effective signal paths that approach transmission-line structures, impedance matching becomes more important. During IC/package co-design, IC and package designers often agree on impedance targets and signal configurations.such as single-ended, differential pair, and coplanar.for routing signals between the die and the package pins. At high frequencies also transmission losses can be a serious issue. Two types of transmission losses exist: skin-effect losses and dielectric losses. Skin effect, which is proportional to the square root of frequency, leads to an increase in conductor dissipation. At high frequencies, significant skin-effect losses degrade signal-waveform amplitudes. In lossy materials within substrate layers, the dielectric constant's frequency dependence leads to dielectric leakage at very high frequencies. As a system's switching speed increases, electromagnetic radiation can produce troublesome EMI. Radiated emissions associated with multigigabit-per-second data rates can introduce noise via signal lines, power and ground planes, and traces. This noise can superimpose itself on signals as they travel between nets, between chips in a single system, and between systems. Avoiding EMI through careful planning is easier, less costly, and faster than trying to correct EMI-induced system misbehavior after you discover it.

      Analogue-digital conversion

      An analog-to-digital converter (also known as an ADC or an A/D converter) is an electronic circuit that measures a real-world signal (such as temperature, pressure, acceleration, and speed) and converts it to a digital representation of the signal. A/D-converter compares the analog input voltage to a known reference voltage and then produces a digital representation of this analog input. The output of an ADC is a digital binary code. By its nature, an ADC introduces a quantization error. This is simply the information that is lost, because for a continuous analog signal there are an infinite number of voltages but only a finite number of ADC digital codes. By increasing the resolution of the ADC, the number of discrete steps is increased, which reduces quantization errors. Some A/D converters sample the input signal continuously, whereas others sample at specific times. Any A/D converter that uses a track/hold buffer must periodically connect its track/hold capacitor to the input signal, causing a small inrush current. All the sampling processes are limited by Nyquist limit. The Nyquist limit is defined as half of the sampling frequency. The Nyquist limit sets the highest frequency that the system can sample without frequency aliasing. In a sampled data system, when the input signal of interest is sampled at a rate slower than the Nyquist limit (fIN > 0.5fSAMPLE), the signal is effectively "folded back" into the Nyquist band, thus appearing to be at a lower frequency than it actually is. This unwanted signal is indistinguishable from other signals in the desired frequency band (fSAMPLE/2). Usually the signals are prefiltered before they enter the A/D-converter to avoid too high frequency signal components which can cause this kind of unwanted signals. In actual practice, you should sample at a rate much higher than two times the Nyquist limit to minimize sampling errors (general rule of thumb is 5 times higher that highest frequency needed to be analyzed well) or you need to provide a very good filter which filters out those "too high" frequency components from your incoming signal. In some special applications frequency aliasing can also be used in an advantageous manner (generally known as "undersampling" method). A digital-to-analog converter (also known as a DAC or a D/A converter) is an electronic circuit that converts a digital representation of a quantity into a discrete analog value. The input to the DAC is typically a digital binary code, and this code, along with a known reference voltage, results in a voltage or current at the DAC output. The word "discrete" is very important to understand, because a DAC cannot provide a continuous time output signal; rather, it provides analog "steps." The steps can be lowpass-filtered to obtain a continuous signal. In D/A conversion process the output of D/A converter is fed through a filter which will remove the image-frequency information (signal higher than 1/2 of sampling frequency) from the output signal. This image-frequency information can distort the output signal. Two methods exist for removing unwanted image signals from the DAC output to prevent alising in a following ADC. First approach is to use a high-performance lowpass filter (data -> DAC -> high-order lowpass filter). For low pass filtering usually a sixth-order lowpass filter is enough.The second methos is to use digital-interpolation filters and a simple analogue filter (data -> oversampling digital-interpolation filter -> DAC -> low-order lowpass filter). The selection of sampling rate to use is an important decision in any system involving sampling. When selecting a sampling rate, there are usually several competing goals, such as:

      • Sample as fast as possible to obtain greatest accuracy.
      • Sample as slow as possible to conserve processor time.
      • Sample slow enough that noise doesn't dominate the input signal.
      • Sample fast enough to provide adequate response time.
      • Sample at a rate that's a multiple of the control algorithm frequency to minimize jitter.
      The truth is there's usually no best answer for all systems, but there's often one answer that stands out as better than most others when the peculiarities of a specific application and the target hardware are considered.
      • 1-bit converters    Rate this link
      • 16-bit ADC provides 19-bit resolution - Many data-acquisition systems require both high accuracy and a fast acquisition rate. With aid of a programmable amplifier before A/D conversion you can get more relative accuracy to the conversion.    Rate this link
      • ADC grounding - Chip designers often internally partition the ground-reference net (or substrate) for an ADC into isolated analog and digital regions for good reasons.    Rate this link
      • Getting the Most from High Resolution D/A Converters - application note in pdf format    Rate this link
      • How to Choose A Sensible Sampling Rate - Trial-and-error testing is neither the fastest nor the best way to determine the sampling rate for a given application, although it's probably the most common. Systematic engineering analysis, plus a few guided experiments, will help you find a good rate quickly.    Rate this link
      • Improved amplifier drives differential-input ADCs - ADCs with differential inputs are becoming increasingly popular. This popularity isn't surprising, because differential inputs in the ADC offer several advantages: good common-mode noise rejection, a doubling of the available dynamic range without doubling the supply voltage, and cancellation of even-order harmonics that accrue with a single-ended input. This document shows shows two easy ways to create a differential-input differential-output instrumentation amplifier.    Rate this link
      • Maximize performance when driving differential ADCs - Converting a single-ended signal to a differential signal before the analog-to-digital conversion can improve the performance of your data-acquisition system. Using differential signals in data-acquisition systems is becoming increasingly popular because differential signals are highly immune to system noise based on the common-mode rejection of a differential ADC. System noise accumulates in signals as they travel across a pc board or through long cables, but this noise does not interfere with the analog-to-digital conversion because the differential ADC rejects any signal noise that appears as a common-mode voltage. Because differential signals cancel out even-order harmonics, they also provide better distortion performance than do single-ended signals. Another benefit is that differential signals double the ADC's dynamic range.    Rate this link
      • Maximize performance when driving differential ADCs - Converting a single-ended signal to a differential signal before the analog-to-digital conversion can improve the performance of your data-acquisition system.    Rate this link
      • Mixed Signal Circuit Techniques - application note in pdf format    Rate this link
      • Multiple ADC grounding - If you have a lot of ADCs on the same board and they all tie to the same digital ground, then the various ADC grounds must all be somehow tied together. In a low-resolution, 8-bit system, which needs only about 60 dB of noise rejection, you can use one big, solid ground plane for all the analog channels and the digital logic. In higher resolution systems requiring more noise isolation, you might worry about stray digital currents flowing across the analog-ground region of your pc board.    Rate this link
      • Sampling rates for analog sensors - Why use trial-and-error methods to determine sampling rates when you can use science and mathematics? Here are the details of a simple procedure that makes more sense.    Rate this link
      • The alias theorems: practical undersampling for expert engineers - Aliasing, long considered an undesirable artifact of an insufficiently high sampling rate, is in fact a useful tool for lab testing and analysis.    Rate this link
      • The beauty of differential drive - Even when sheer chaos is breaking out around an ADC, differential-drive techniques can make the converter perform quietly    Rate this link
      • Using PWM to Generate Analog Output - Pulse Width Modulation (PWM) modules, which produce basically digital waveforms, can be used as cheap Digital-to-Analog (D/A) converters only a few external components. A wide variety of microcontroller applications exist that need analog output but do not require high resolution D/A converters. Some speech applications (talk back units, speech synthesis systems in toys, etc.) also do not require high resolution D/A converters. For these applications, Pulse Width Modulated outputs may be converted to analog outputs. Conversion of PWM waveforms to analog signals involves the use of analog low-pass filters. This application note describes the design criteria of the analog filters necessary and the requirements of the PWM frequency. Later in this application note, a simple RC low-pass filter is designed to convert PWM speech signals of 4 kHz bandwidth.    Rate this link
      • Multiple ADC grounding - If you have a lot of ADCs on the same board and they all tie to the same digital ground, then the various ADC grounds must all be somehow tied together.    Rate this link
      • What does the ADC SNR mean? - ADC's ideal SNR is 6.02N+1.76 dB (excluding delta-sigma converters). Where does this ideal formula come from, and how do you measure SNR with a real ADC?    Rate this link
      • DDS IC plus frequency-to-voltage converter make low-cost DAC - Precision DACs are essential in many consumer, industrial, and military applications, but high-resolution DACs can be costly. Frequency-to-voltage converters have good nonlinearity specifications?typically, 0.002% for the AD650?and are inherently monotonic. This Design Idea shows how you can use a frequency-to-voltage converter and a DDS (direct-digital-synthesizer) chip for precise digital-to-analog conversion. The DDS chip generates a precision frequency proportional to its digital input. This frequency serves as the input to a voltage-to-frequency converter, thereby generating an 18-bit analog voltage proportional to the original digital input.    Rate this link
      • Buffer adapts single-ended signals for differential inputs - DC coupling of single-ended signals into differential-input, single-supply ADCs can be challenging. The input signal requires level shifting from ground to VS/2 as well as single-ended-to-differential conversion. In addition, you must balance the differential inputs of the ADC to cancel even-order harmonics and common-mode noise. Systems often require this signal translation to take place without injecting dc bias currents back into the signal source. Processing wideband signals with large dynamic range (12- to 14-bit ADCs) can also add to the circuit complexity. Wideband amplifiers address nearly all these issues, but their standard implementation requires the use of ac coupling. This Design Idea describes a new circuit that eliminates this requirement through the use of an external dc feedback loop. It also allows the lower end of the passband to extend to dc. The basis of the circuit is a simple level-shifting circuit.    Rate this link
      • An overview of data converters - Digital communications, digital instruments and displays have created a demand for low cost reliable converters that can convert signal between analogue and digital formats. This application note AN100 from Philips gives you an overview of A/D and D/A conversion technologies.    Rate this link
      • Combine two 8-bit outputs to make one 16-bit DAC - Inexpensive, 16-bit, monolithic DACs can serve almost all applications. However, some applications require unconventional approaches. In this circuit two PWM outputs from a microcontroller combine to form a monotonic 16-bit DAC.    Rate this link

      Protecting ideas and intellectual property

      By 'intellectual property? we mean intangible legal rights which may be protected by patents, copyrights, trademarks, and trade secrets. Today in electronics industry a good engineer needs to know documenting and promoting the protection of intellectual property (IP) associated with a given product line. The major players in the electronics industry realize that to be successful in this business requires that IP be cultivated and harvested in parallel with the technical advances generated by the research and development staff. There are different protection mechanisms:

      • Trade Secret: Trade secret can be a formula, pattern, cimpilation, program, device, method, technique or process that derives independent economic value. The information must kept secret, which can be hard.
      • Copyright: A copyright owner has the exclusive right with respect to the copyrighted work of (a) reproduction, (b) preparation of derivative works, (c) distribution of copies, (d) performance of the work publically, and (e) public display of the work. The rights given to a copyright owner attach on creation or 'fixation? of the work in a tangible medium. Copyright protection may be appropriate for the expression of ideas such as PLD/FPGA source code, schematics, program listings, etc., it is inappropriate to protect the ideas that these entities embody.
      • Trademarks: Trademarks are used within our economy to protect consumers from confusion regarding the source, quality, or origin of goods or services. The right given a trademark owner to exclude others who might use marks which tend to confuse the public is a right which is acquired by use of the mark to which protection is sought.
      • Patents: Patents provide a right of exclusion to prohibit the sale, offer for sale, manufacture, import, or use of a device which is covered by the patent without the permission of the patent holder. While this exclusionary right may be narrowly tailored by the claims in the patent, the goal in any properly written patent is to stake out as broad an area of product coverage as possible. Key to this is a properly written technical description (disclosure) of the invention.
      You must understand those different protection mechanism to be able to understand when to use which.