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High precision SAR ADC operates in noisy environments

7th April 2017
Caroline Hayes
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Designed for precision measurement applications, the LTC2500-32, 32bit successive approximation register (SAR) analogue to digital converter (ADC) blends high accuracy and speed. The device was announced by Analog Devices, which recently acquired Linear Technology Corporation.

The device is based on Linear Technology’s proprietary SAR ADC architecture with flexible integrated digital filters to optimise system signal bandwidth and analogue anti-aliasing filter requirements. The ADC simultaneously provides two outputs, a 32bit low noise digitally filtered output that achieves up to 148dB of dynamic range and a 32bit, 1Msample/s no latency output comprising an over-range detection bit, a 24bit representation of the input voltage difference, and a 7bit representation of the common mode input voltage.

The no latency output is matched to the digitally filtered output, avoiding the mismatch and drift that typically occur in applications requiring an additional, faster ADC to monitor signal integrity in parallel with a precision ADC. The wide input common mode range and high common mode rejection rate (CMRR) enable the ADC to interface signals with varying common mode, simplifying the analogue signal chain. Each output provides an accurate representation of the voltage difference applied between the two input terminals.

The low noise density of the ADC produces 148dB of dynamic range at 61sample/s and 104dB at 1Msample/s. The ADC also claims to have unrivalled linearity of 0.5ppm typical and 2ppm guaranteed maximum INL value, together with low gain and offset drift over wide temperature ranges. The combination of these features enables precision measurements in noisy environments, such as in industrial automation applications. The integrated configurable digital filter offers seven filter types and 13 down-sampling factors, providing flexibility to trade bandwidth, filter response and noise performance for each application.

The LTC2500-32 is available now in commercial and industrial (-40 to +85oC) temperature grades. The DC2222A evaluation board for the LTC2500 SAR ADC family is also available.

 

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