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Addressing a bottleneck in the A/D chain

With numerous recent developments across its analog-to-digital converters (ADC) portfolio, Texas Instruments used Embedded World to refocus attention to matters early on in the signal path – notably, towards the ADC buffers/drivers that have become an apparent bottleneck in the A/D chain.

The company was demonstrating the THS452x at the show, a family of drivers that cater to single and multichannel successive approximation register (SAR) and delta-sigma ADCs up to 24bits. This driver family sits in the middle of TI's ADC offering, catering to consumer, industrial, automotive and even telecoms applications alike ” all situations in which fully differential data acquisition is required, explains Christoph Gromann, TI's Analog marketing manager, EMEA. In the past, integrators might have used two amplifiers or a single amplifier in a dual configuration to deliver this capability, requiring impeccable matching of the signal on the two channels. The THS452x family, available in single, dual and quad configurations, avoids these matching concerns and results in a simpler circuit design.

The THS452x range consumes quiescent current of 1.14mA/channel and has power down current of 20uA – TI claims these figures represent half and 22 times less than the competition respectively. Bandwidth is 145MHz and slew rate 490V/us. Providing increased dynamic range and sensitivity, this part has an input voltage noise of 4.6nV/rtHz. Other features include output common mode control, which allows for easy DC coupling, while negative rail input and rail-to-rail output capability should simplify the design process.

The catalyst for many of TI's ADC and driver developments is that sensors that deliver a small output voltage are increasingly being used in relatively noisy environments e.g medical, industrial. This situation has led to the combined requirement for high resolution and precision A/D conversion, good dynamic range and the need to cater to sensitive power budgets ” not an easy balance to achieve. Key to the THS452x's metrics, says Gromann, is TI's BiCom3 process in Freising, Germany. This bipolar SiGe process also has a high voltage extension that suits industrial applications.

As Gromann concludes: “All this is about achieving the best signal integrity possible before making the conversion into digital.” We should expect to see more focus from all ADC manufacturers on buffering going forward.

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