Analog Hotspot

WILLIAM GRILL, Honeywell Aerospace-Olathe, Olathe, Kansas william.grill@honeywell.com Over the years, many sensor monitor designs would have benefited by being able to have their encoded pulse-width modulation (PWM) data forwarded to and post-processed by a PC-based host. However you encode the PWM information, the PWM-to-RS-232 translator described here has a small footprint and a total cost under a few...

Sometimes less is more. Here, a quarter-step switching logic sequence for stepper motors offers several significant advantages over full-and halfstep modes—higher resolution, smoother drive, minimal resonance effects, and reduced settling time. The method uses a 16-step input sequence to produce 1600 steps per revolution in 400-step motors. At the heart of this quarter-step technique is a so-called half-excitation state, during which the ratio of motor current ...

Lots of modern monitors feature an indication of incoming video signals, even if the monitors are switched off. In most cases, an LED provides this indication by fading (slowly increasing and decreasing) its light intensity. This type of indication is very specific, and thus convenient, for use in other devices for the same purpose. Monitors typically stay connected to the power line, even when they're switched off. However, this doesn't apply for all video devices. Some may need...

Use of pipeline analog-to-digital converters (ADCs) continues to expand, both as standalone parts and as embedded functional blocks in system-on-a-chip (SoC) ICs. They boast acceptable resolution at high-speed operation and can be integrated onto relatively small die area. Driven by IC chip cost factors, many commodity CMOS-technology SoCs now include embedded pipeline ADCs. Pipelined converters attain their final resolution through a series cascade of lower-resolution stages. For...

In low-end audio systems, digital potentiometers can be used as audio attenuators or amplifiers (Fig. 1). Unfortunately, a large change in volume at an arbitrary time can cause an abrupt discontinuity in the audio signal. The result is audible clicking, or zipper noise, which precludes the use of this simple design in mid-level or high-end audio systems. But designers can reduce zipper noise by converting the random change in...

Designing total-harmonic-distortion (THD) measurement into a system usually involves a notch filter and a broadband ac measurement. The problem with this technique is that it measures both THD and noise. DSP-based test equipment can calculate just the THD, but this isn't practical for most portable equipment. However, system designers can add THD measurement capability by using a bank of band-pass filters set at the harmonics of the fundamental, along with a notch...

Working on an embedded project? An 8-bit microcontroller with a pulsewidthmodulation (PWM) peripheral can provide a low-cost and easy solution to adding natural voice to your next embedded endeavor. We recently implemented this technique in SuitSat-1 (see "Latest Radio Amateur Satellite Is No Empty Suit," March 16, 2006, p. 25). Listeners could hear recordings of schoolchildren saying "greetings from space," as well as telemetry readings (time, temperature, and battery...

Many times, the need arises to interface single-supply analog-to-digital converters (ADCs) and comparators to real-world signals like 5 V. Of course, it's possible to condition the signal using operational and/or instrumentation amplifiers. But few engineers realize that it's often possible to achieve the level shifting using a resistor network (Fig. 1). Critics of this technique point out that the resistor network can load the...

There is no doubt that the challenge of designing analog integrated circuits gets more intense every day. Market demand and price pressures for end products reduce the design time . Add to that demanding performance and frequency requirements and burgeoning manufacturing issues and you have a potentially volatile mix. Although there' s plenty of ?time-to-market? talk, an increasingly important metric is time-to-yield. As a result, the analog portion of a design becomes critical to meet these...

The increasing number of audio and video sources (VCR, DVD, set-top box, etc.) in a typical home-entertainment system requires a simple way to select the desired source. The add-on mechanical switches available today are bulky and prone to contact wear, resulting in degraded performance over time. Solid-state analog switches solve this problem. But passive switching can produce an annoying thump as ac-coupling capacitors get charged and discharged by the make-and-break action of...

Function generators often play a critical role in the design, testing, and operation of encoders, modulators, demodulators, and measurement instruments. Here's an inexpensive way to build a bus-controlled sinewave oscillator that has downright low distortion. The circuit generates a sinusoidal output with typical second and third harmonics down from the fundamental by -76.1 and -74.2 dB, respectively, across its full output range of 10 Hz to 10 kHz. That performance represents...

Frequency mixers are often implemented using a diode bridge or a Gilbert cell. Both types of mixers use a local oscillator (LO) to flip the polarity of the radio-frequency (RF) input. When the LO is positive, the RF input passes to the intermediate-frequency (IF) output without being reversed. When the LO is negative, the RF input is reversed as it passes to the IF output. So, the LO "flips" the polarity of the RF signal. This has the effect of multiplying by +1 or 1 (neglecting losses)....

The growing popularity and availability of high-definition television (HDTV) is creating a small revolution in the video industry. New video systems must be capable of handling the standard National Television System Committee (NTSC) composite signal as well as high-definition signals. Also, low-cost and low-power concerns drive system designers to find the simplest solutions. Here's a one-transistor network that lets a single video sync separator operate for both HDTV...

In the days of large split supplies, it was relatively easy to make a good monostable multivibrator. Even 5-V single supplies posed only a moderate challenge. Making a good one-shot to run on 3.3 V is more difficult, though. The variation of CMOS thresholds limits their usefulness for precise timing. Plus, limited voltage " headroom" can make designing a good reference plus comparison circuitry difficult outside the environment of monolithic matched parts. However, newer devices...

Ken Yang was working at Maxim when he submitted this Design Brief. (He's since moved to the power group at a network equipment company.) The circuit turns on emergency lighting (in the form of a string of white LEDs) and turns them off again after about 10 minutes. The objective is to give personnel time to safely exit the building when a power outage occurs and then to shut off the emergency light to conserve battery power. Yet unlike the emergency lights most of us are used to,...

Circuit and system design requirements often mean compromises. For example, optoisolators are used almost everywhere, but they are highfrequency limited. This simple circuit allows for wider bandwidth at the cost of two transistors and two resistors. And it's all done with mirrors! With conventional approaches, the resulting design isn't always optimized for high speed. In certain situations, the optoisolator load-resistor value might be higher than the value that provides the...

Medical and industrial applications often require galvanic isolation of 2500 V ac or higher for the safety of patients and equipment operators. The isolation barrier conveys not only power to the sensing element, but also data to or from that element. Each data signal crossing the barrier-requires isolation. Consequently, designers can typically save costs in these applications by choosing a serial bus rather than a parallel bus. Serial buses include SPI, I2C, and the...

The semiconductor industry’s rapid move toward a 90-nm process node to achieve performance and cost benefits puts enormous pressure on power budgets. Decreasing transistor sizes lead to increased leakage current and, as a result, static power. Dynamic power also rises with system speeds and higher design density, but in a more linear fashion. Today, many designs have 50-50 static and dynamic power dissipation. According to International Technology Roadmap for Semiconductors (ITRS)...

Simply adding a diode and potentiometer to a 555 timer operating in the asynchronous mode yields a pulsewidth modulator (PWM) with a duty factor adjustable from 1% to 99% (Fig. 1). Applications would include speed control of electric motors where the switching drive can be power efficient. The output of this circuit could drive a MOSFET to control the current through the motor, resulting in smooth control of the motor speed at...

The figure shows a schematic for an oscillator amplitude-control servo system. The circuit creates a closed-loop system that supplies a fixed and adjustable peak-to-peak amplitude ac signal centered around 0 V. A 1-kHz sine wave, labeled AC_INPUT, is ac-coupled to an AD633 multiplier chip. Then the AC_INPUT is multiplied by the SERVO signal. The multiplier's output is a scaled version of the AC_INPUT. This 1-V sine output signal is fed into a peak detector, and the peak of the...