Predictive maintenance & condition monitoring


Figure 8. The ADAQ7768-1 functional block diagram


resolution, as seen in Table 2 and Figure 9. Figure 10 illustrates how an iPassives network achieves its close matching from fabrication, expressing the difference in resistance through the colour gradients. iPassives resistor tolerance can go below 0.1 per cent, while temperature coefficient of resistance (TCR) can be matched less than 1 ppm/°C, translating to a tightly controlled RC filter bandwidth that is stable across temperature. With


the use of iPassives network, µModule solutions solve the phase mismatch problem through the BOM and assembly approach, setting a new level of performance that is limited in traditional discrete signal chains.


GENERICS AND DISTINCTION There are other generics from the ADAQ7768-1 that use the same integrated ADC, namely the ADAQ7767-1 and the ADAQ7769-1 (Figure 11).


ADAQ7768-1 The ADAQ7768-1 includes a fully differential PGIA. With its high impedance and low input bias current, it connects directly to various sensors. Unlike a conventional voltage feedback amplifier, the integrated PGIA maintains nearly the same bandwidth across all its gain settings— leading to tight device-to-device phase matching regardless of the gain setting.


ADAQ7767-1 The ADAQ7767-1 does not provide an integrated input amplifier - lowering cost and enabling the customer to provide custom input signal conditioning. This device has three input ranges, with a maximum of ±24 V for single-ended inputs, allowing a DC-coupled IEPE sensor architecture and a simpler power solution.


Instrumentation Monthly October 2024


Figure 9. The ADAQ7768-1 device-to-device phase angle mismatch at 20 kHz across temperature, normalised to mean value at 25°C.


ADAQ7769-1 The ADAQ7769-1 builds upon the ADAQ7767- 1 by adding a single-ended programmable gain low noise amplifier. It is still capable of the ±24 V single-ended input range, allowing a DC- coupled IEPE sensor architecture with a more complete solution.


IMPLEMENTING SYNCHRONISATION To obtain the full phase matching performance of these products, it is required that the device follows proper methods of synchronisation. While there is a generic method of synchronising various products, some devices have their own unique methods that are usually added as a benefit to the overall system. Generally, in many SD ADCs, a SYNC or SYNC_IN pin is provided to allow a controller to


Figure 10. ADI’s iPassives resistors have tighter tolerance and matching compared to discrete resistors.


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