Analog Devices has introduced a multiplexed 24-bit sigma-delta A/D converter designed for process automation and instrumentation systems, where data channel density is increasing and channels must be monitored faster. Analog Devices claims that the converter doubles the throughput rate of alternative sigma-delta converters while dissipating less power and achieves a 50-kSPS (thousand samples per second) multi-channel scan rate.

In the real world, signals are analogue – light, sound, temperature, you name it. Hence, these real-world signals must be converted into digital using A/D (Analogue-to-Digital) converters before they can be manipulated by the digital equipment. A/D converters are the most widely used devices and are virtually used everywhere where an analogue signal has to be processed, stored or converted into digital form. They are integral to the current music reproduction technology and are incorporated within microcontrollers. The resolution of the converter indicates the number of discrete values it can produce over the range of analog values.

“Depending on the precision requirement, the right converter should be picked,” says Somshubhro Pal Choudhury, managing director, Analog Devices India. It is important to provide fast and high resolution conversion information when sampling industrial level signals. Choudhury adds, “There is, as expected, somewhat of a trade-off between speed and precision. For high precision, the input value must necessarily be held constant during the time the converter does the conversion which means the throughput is lower.”

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Traditionally, the highest resolution analogue-to-digital converters (ADCs) available at sampling rates up to 500 kSPS were 14 bit to 18 bit. This new Sigma Delta AD7176-2 A/D converter keeps the high precision and doubles the throughput rate. This converter is designed for process automation and instrumentation systems where data channel density is increasing and channels must be monitored much faster than ever before without losing the precision. Each of the two differential or four pseudo-differential channels can be scanned at a rate up to 50 kSPS with 17.2 bits of noise-free code resolution, while providing precision of 24-bit conversion from Analog to Digital.

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Interesting features of the new AD7176-2 24-bit sigma-delta A/D converter
The key features of this component are 5-SPS to 250-kSPS output rate for fast and flexible updates and 17.2 noise free bits at 250 kSPS for more accurate measurements. It also features up to 90-dB of 50-Hz and 60-Hz line frequency rejection using enhanced 50-Hz and 60-Hz rejection filters and a total current consumption of 7.8-mA. Moreover, in scenarios which require fast scanning of analog input channels using the internal/external multiplexer, high resolution at lower speeds in either channel scanning or ADC per channel applications and Single ADC per channel, this A/D converter can be used.

Ultimately, the distinguishing and unique feature of the AD7176-2, which demarcates itself from other 24-bit ADCs, is that it offers the user a fast settling of about 20 microseconds for high resolution, multiplexed ADC with high levels of configurability.

Circuit Description
The AD7176-2 includes two separate linear regulator blocks for both the analog and digital circuitry and a precision 2.5 V low drift (2 ppm/°C) band gap internal reference. It can have up to four active channels – either as two fully differential or four single-ended analog inputs. The AD7176-2 has three independent power supply pins: AVDD1, AVDD2, and IOVDD.

It also offers three key digital filters. The fast settling filter maximises the channel scan rate. The Sinc3 filter maximises the resolution for single-channel, low speed applications. For 50 Hz and 60 Hz environments, the AD7176-2 specific filter minimises the settling times or maximises the rejection of the line frequency. The AD7176-2 has a 3- or 4-wire SPI interface that is compatible with QSPI, MICROWIRE, and DSPs.

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The AD7176-2 has five analog input pins: AIN0, AIN1, AIN2, AIN3, and AIN4. Each of these pins connect to the internal crosspoint multiplexer, which selects any analog input combination as the input signals to be converted, routing them to the modulator positive or negative input. The specified operating temperature range is −40°C to +105°C. The AD7176-2 is housed in a 24-lead TSSOP package.

Applications
The AD7176-2 can be used across a wide variety of applications, providing higher resolution and accuracy conversion. Some applications for the AD7176-2 Sigma-Delta A/D include process controls (PLC/DCS modules), medical, and scientific multi-channel instrumentation and chromatography.

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Pricing and Availability
The AD7176-2 is currently available, and you can get samples from Analog Devices. It comes in a 24-lead TSSOP package with a channel configuration of four pseudo or two full differential. The price is $10.25 for a unit of 1000 quantity.


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