“This document focuses primarily on implementing a high-performance data acquisition system (DAS) through the optimal integration of industrial sensors and high-performance ADCs. It is possible for high performance ADCs to use the Sigma-Delta architecture in their designs. This reference design will explore Maxim’s MAX11040K and the correct schematics and components required for optimal performance.
This document focuses primarily on implementing a high-performance data acquisition system (DAS) through the optimal integration of industrial sensors and high-performance ADCs. It is possible for high performance ADCs to use the Sigma-Delta architecture in their designs. This reference design will explore Maxim’s MAX11040K and the correct schematics and components required for optimal performance.
Many new advanced industrial applications require high-performance data acquisition systems (DAS) and interfaces between multiple sensors. These industrial applications can take advantage of very high dynamic range, simultaneous sampling, multichannel ADCs such as the MAX11040K when the interface requires multichannel high precision magnitude and phase information.
Advantages of High Speed Sigma-Delta Architecture
Take the advanced three-phase power line monitoring/measurement system shown in Figure 1 as an example. These industrial applications require accurate simultaneous multi-channel measurements over a wide dynamic range of up to 117dB at sampling rates up to 64ksps. To optimize system accuracy, the signals from sensors (such as the CT and PT transformers in Figure 1) should be properly “conditioned” to meet the ADC input range and ensure that the DAS characteristics enable measurements that comply with international standards.
Figure 1 illustrates that two MAX11040K ADCs can simultaneously measure three-phase and neutral voltages and currents. The ADC is based on a sigma-delta architecture that uses an oversampling/averaging process to achieve high resolution. Each ADC channel uses a dedicated switched capacitor sigma-delta modulator to perform analog-to-digital conversion on its input. The modulator converts the input signal into low-resolution digital data whose average value represents 3.072Msps of digitized signal information at a 24.576MHz clock. This data stream is then presented to an internal digital filter for processing to remove any high frequency noise. The result of these operations is a high-resolution 24-bit output data stream.
The MAX11040K is also a 4-channel simultaneous sampling ADC whose output data represents the processed average. These values cannot be considered “instantaneous” like successive approximation register (SAR) ADCs.
In power line applications
The ADC performance requirements of the CT (current) and PT (voltage) sensor transformers in this application are typically ±10V or ±5V peak-to-peak (VP-P). The ±2.2VP-P input range of the MAX11040K is lower than these typical outputs of CT and PT transformers. However, there is a simple and cost-effective way to use the MAX11040K’s lower input range to accommodate the transformer’s ±5V or ±10V range. as shown in picture 2.
The circuit connected to channel 1 represents a single-ended design. In this configuration, one side of the transformer is grounded and signal conditioning is accomplished with a simple resistor divider and capacitor.
If common-mode noise (same noise at both ADC inputs) is a serious concern, a differential design as shown in the circuit connected to channel 4 is recommended. By utilizing the MAX11040K’s true differential inputs in this design, noise effects are reduced.
A high-performance multichannel data acquisition system (DAS) can be implemented using Maxim’s MAX11040K ADC, which uses a sigma-delta architecture in its system. This would be ideal for “smart” grid monitoring systems where proper signal conditioning is highly required.