Analog Hotspot

How does direct digital synthesis (DDS) work? There are at least three elements to DDS: a numerically controlled oscillator (NCO) with a phase modulator, a block that converts the phase information to amplitude values, and a digital-to-analog converter (DAC). An inphase/quadrature (I and Q) modulator may be added ahead of the DAC? What are the advantages of DDS? The digital nature of DDS technology provides...

Dear Bob: I have a little microcontroller circuit powered from a 115-V ac to 24-V dc supply that is then further stepped down to 5 V with a buck converter. An RS-232 converter, whose switched capacitors give 8-V swing, is used to communicate to a PC. The problem I have is that connecting to a grounded PC has blown out the serial port on the PC. We grounded the common in the circuit and have had no problems since. I'm looking to understand what possibly could have happened....

A functional replacement for Toshiba's discontinued 2SK389 low-noise dual JFET is available from Linear Integrated Systems, which devotes itself to specialty semiconductors. In fact, the LSK389 series of 1-nV n-channel monolithic dual JFETs improves upon the original. When it was available, Toshiba's 2SK389 was used in audio amplifiers and preamps, discrete low-noise operational amplifiers, and battery-operated audio preamps. It also went into audio mixer consoles, acoustic...

On the manufacturing floor, digital isolators permit high-speed data transmission in the presence of rotating machines and other sources of large magnetic fields. In high-impedance circuit paths, isolation causes noise to appear across the isolation barrier, rather than at the receiver or more sensitive components. It also provides patient protection in medical applications and breaks potential ground loops between distant nodes. Previous isolators have been based on LEDs and photodiodes,...

The state of the art in class D amplification has progressed rapidly in the past few years, most noticeably for lowerpower applications that require less than 50 W per channel. Class D is inherently more efficient than the traditional class AB amplifier because the output stages are always on or off, with no intermediate bias stage necessary. This efficiency advantage has never held widespread appeal for designers, since the disadvantages of higher parts cost, poor audio...

Hi Bob: Back in the early '70s, I was an EE major at Lowell Tech in Lowell, Mass. Within easy walking distance of the dorms, there was an electronics surplus store in one of the old textile mill buildings. One day I found some Philbrick P65AU op-amp modules there. I bought several of them, for maybe $5.00 total. (A bargain. /rap) I decided to build a stereo hi-fi amp around them. It took the better part of the semester to build it, and I nearly flunked...

When it comes to touchpads, most OEMs buy complete subassemblies from outside vendors, essentially subcontracting the electronic design as well as the assembly. The AD7142 capacitance-to-digital converter from Analog Devices may change that, allowing OEMs to reduce bill-of-materials costs while absorbing a small increase in nonrecurring-engineering costs. Housed in a 5- by 5-mm lead-frame chip-scale package, this 14-channel, 16-bit chip fits touch-pad input...

What applications require precision op amps? Precision amplifiers originally evolved to fill the needs of the test and measurement community. This arena demanded test system elements with much more precision than the original instruments were intended to make. They also required a set of specifications and ways of verifying those specs that unquestionably demonstrated that superiority. Today, precision amps are widely used in automotive and industrial applications,...

I was down at an "Arrowfest" in Plano, Texas, a few months ago. We had a little panel session about the future with Bill Klein of Texas Instruments, Arnold Williams from Analog Devices, and myself. Most of the audience agreed with the three of us (and the moderator)—the future will have a lot of analog. When we see that the power-supply drain of a fast processor at 0.09 µm is largely related to the device leakages—which aren't very predictable and can't be...

HDTV needs amplifiers, data converters, and matrix switches to handle legacy analog content. New analog/mixed-signal chips cost less, use less power, and meet dual-supply specs while running off a single, lower-voltage supply rail. WiMAX defines new RF-mixer requirements, but as GSM evolves, it needs new mixer designs too. In the U.S., new regulations that let regional Bell operating companies compete with cable to deliver video...

If you want to know what's going on, ask the folks with the most feet on the street. I spoke with engineers at several major companies to get a feel for what's in store for the analog/mixed-signal arena in 2006. Once again, consumer applications are the big drivers. This year, new video modalities are pushing innovation. Flat-panel display technology prices continue to plummet, but big screens come with big challenges. Artifacts created in the imaging, compression, decompression,...

Still the architecture of choice for "near-dc" sampling and greater than 20-bit resolution, delta-sigmas built using fine-geometry process technologies are moving in on the pipeline ADC's turf. Companies are innovating with other architectures, too. The folding/ interpolating architecture made a comeback in 2005, and other types of paralleled interleaving pipelines and SARs are in the works. The preferred process geometry for pipelines and SARs is...

One significant development in the world of analog-to-digital converters (ADCs) has nothing to do with how they're built and everything to do with how they're supported. Companies now recognize that the entire conversion signal chain—front end, clock, and data converter—must work together. So, they're providing comprehensive tools that help ensure a successful design. Some of these tools are Web-based, like National's Webench and Analog Devices' simADC and simCLK....

Satellite radio provides new opportunities for DDS in the receive chain. In portable media players and in cars, multiple audio sources and output channels encourage chipmakers to integrate. As with ADCs, DAC designers wrestle with clock jitter. CMOS continues to dominate DAC process technology, though some of it is becoming silicon-germanium CMOS....

To borrow a line from the Talking Heads' David Byrne, the basic digital-to-analog converter (DAC) is the same as it ever was. In today's designs, though, DACs rarely stand alone. They tend to be integrated into codecs and directdigital-synthesis (DDS) chips. Codecs constitute a major new market for dc-enabled baseband devices, particularly for signal decompression in cell phones and personal media players. Meanwhile, one thing is new. Engineers are pushing DACs to...

Applications for precision op amps are on the upswing, particularly in the automotive market, driving prices down. At the same time, offsets, noise, and temperature coefficients are improving even further. The latest amplifiers are more layout-tolerant than their predecessors. Only a single supply rail on the board? That's okay. The amplifier chip itself can generate the voltages it needs. Automakers are still leery of Class D...

Let's begin with some broad observations. Precision amplifiers, originally designed for test and measurement equipment, recently migrated to sensor monitoring in automotive and industrial applications. The latest performance-monitoring subsystems in cars and factories need the precision amps' low-input offset voltage and offset current with low temperature coefficients and noise characteristics. High-speed amps, traditionally boasting at least 50 MHz of bandwidth and at least...

Where do I need analog and flash memory in a digital system? Many systems accomplish most of their tasks using digital logic. But the logic chips themselves?FPGAs, ASICs, ASSPs, etc.?all require some analog support. That support takes the form of power-sequencing control, voltage sensing to detect brownout conditions, power management, and temperature sensing to provide dynamic control of fan speed, clock speed, and even operating voltage. For example, power...

There's hype, and then there's reality. When it comes to leading-edge chips, the chasm between the two is rather wide. Reverse engineers tear these technologies apart for a perspective that often diverges far from commentaries offered by the chipmakers and other industry mavens. Processors Last year was full of hype about the impending release of 65-nm devices, particularly in the microprocessor and consumer arenas. Intel shipped its dual-core Yonah...

The wireless infrastructure market may demand the highest and most aggressive performance requirements for analog and mixed-signal devices. Relative to mixers, some people I spoke with see a swing back and forth between established GSM and upstart WiMAX for the technology driver's seat. That's interesting, because cellular industry pundits always seem to be predicting that the demand for GSM is about to plateau. Some companies say penetration will continue to grow for the forseeable...