Review

While representing three of the oldest and most widely used semiconductor circuits, a/d and d/a converters and op amps continue to chalk up significant gains in price reductions, which mainly impact low-end devices, and improved performance, mainly seen in high-end devices. Overall, the analog market continues to be a hotbed of R&D activities, with much of the activity spurred on by the mushrooming amounts of data the analog devices must carry and process between real and digital worlds. Here is a sampling of new ADCs, DACs and op amps to enter the market over the past year that are helping efficiently bridge these two worlds.

Developed for use in critical measurement applications, the Texas Instruments' (ti.com) ADS1605 16-bit, delta-sigma ADC boasts of a data rate of 5 Msamples/s, a SNR of 88 dB, a THD of -99 dB, and a SFDR of 101 dB. Operation is from a 5V analog supply and 3V digital supply, while the digital I/O operates from a 2.7V to 5.25V supply to support a wide range of logic families. Power dissipation is set by an external resistor and can be reduced from 315 mW to 570 mW when the device is operating at slower speeds. When not in use, the converter can be powered down via an I/O pin.

Designed for high-resolution measurements in portable products, the ADS1244 a/d converter, also from Texas Instruments, consists of a third-order delta-sigma modulator having a ±5V differential input stage and a digital filter that rejects 50/60 Hz signals, settles in one cycle, and outputs data at a 15-sample/s pace. The 24-bit ADC comes in a MSOP-10 package and also features a two-wire serial interface, power consumption of less than 270 µW in operation and less than 1 µW in sleep mode, and support for 2.5V to 5.25V analog and 1.8V to 3.6V digital supplies. And multiple ADS1244s can be connected together to create a synchronously sampling multi-channel measurement systems.

On the DAC scene, Analog Devices (analog.com) developed this year an octal d/a converter in a slimmed down package, the AD534x family. The 8-bit AD5346, 10-bit AD5347 and 12-bit AD5348 integrate eight parallel interface DACs and operate from a 2.5V to 5.5V supply, with typical power consumption being 1 mA (1.65 mA at 5.5V). Output voltage is adjustable from 0V to VREF or 0V to 2 x VREF in either buffered or non-buffered modes. Input data is double buffered to allow simultaneous updating of all eight converters by way of an LDAC pin. The DACs come in 6 x 6-mm chipscale (CSP) or 38-lead TSSOP packages.

Another DAC example is the MAX5888A from Maxim Integrated Products (maxim-ic.com). This 16-bit LVDS d/a converter employs a current-steering architecture that supports a full- scale output current range of 2 to 20 mA and allows a differential output voltage swing between 0.1 and 1 Vp-p. It has a spurious-free dynamic range (SFDR) of 76 dBc at a 40 MHz output. The 68-pin device operates from a 3.3V supply and supports update rates of 500 Msamples/s. Power dissipation is 250 mW at 500 Msamples/s and 130 mW typical at 100 Msamples/s. The DAC also has an integrated 1.25V bandgap reference and control amplifier and a separate reference input pin.

On the op amp scene, the LT6011 dual rail-to-rail op amps from Linear Technology (linear.com) exemplified how power stingy these devices can be. Operating on 2.7V to 36V, the devices draw just 135 µA of supply current each. Other features include an input offset voltage of below 75 µV, input bias current of less than 0.9 nA, and a noise voltage density of 14 nV/Hz. Minimum open loop gain is 120 dB and CMRR is beyond 115 dB. Maintaining accuracy over temperature and time, the dual op amp has an input offset voltage drift of 0.8 µV/°C with a long-term stability of 0.4 µV per month.

Representing high slew-rate CMOS op amps are the ALD2724 and ALD2724E from Advanced Linear Devices (aldinc.com). The former is pre-programmed at the factory to achieve minimum Vos, while the latter has a guaranteed input offset programming range of ±5 mV and is recommended for applications requiring electrical user-programming for further Vos trimming. Standard offset voltage specs for both devices are typically 25 mV at 0.01 pA input bias current. And both devices feature rail-to-rail I/O voltage ranges and ±5V supply operation.

With a nod towards low-voltage designs, such as battery-operated products, the 1-MHz MCP6001 single, MCP6002 dual and MCP6004 quad op amps operate on supply voltages down to 1.8V with a typical power consumption of 180 µW. Developed by Microchip Technology (microchip.com), the low-cost ampifiers provide rail-to-rail inputs and outputs and have a 90° phase margin into a 60 pF, 10 KÙ load, promising to minimize design considerations and the need for stabilizing components.

—Joe DelGatto

Outlook

Analog Device Families Grow More Specialized
The ever widening use of electronics to monitor and control events in the physical world promises to trigger development of a host of new a/d and d/a converters and op amps, with the performance of many of the devices groomed for specialized applications. For converters, but especially mid- to high-end devices, look for increases in speed and resolution, faster sampling rates, lower power supply voltages and power dissipation, and increased levels of integration, such as by implementing various interfaces and sensor-specific circuitry on-chip for ADCs and improved digital-related performance for DACs. And for op amps, look for lower power dissipation, higher operating speeds, wider operating supply ranges, smaller packages, including development of chip-scale types, and further advances in differential, precision, instrumentation, and other specialized amplifier types.

—JDG