Isolated ADC: High-precision and high-performance ADC under the integration of isolation technology

The analog-to-digital converter ADC connects the real analog world and the electronic system, and has always been the jewel in the crown of the chip industry. With the development of technology applications, the ADC industry has shown an increasingly clear development trend. High sampling rate, high resolution, and low power consumption are the future development directions. Isolated ADC, as a very representative product in the ADC category, is one of the examples of ADC performance breakthroughs and high integration simplifying the design burden because of its isolation technology that enhances performance and extends its service life. For isolated high-performance ADCs, the isolation technology must pay attention to isolating the clock on the one hand, and isolating the power supply on the other. The clock isolation of ADC (sampling clock or conversion signal) is to prevent the hot end from generating a clock, and at the same time, for high performance, the clock needs to be jitter-free; the isolated power supply is usually within the range of 10 W. Generally, flyback converters or Push-pull converter.
In fact, there is also a data isolation, which can be achieved through a digital isolator. Just connect the SPI signal SPI clock, SDO, SCK and Busy to the data isolator to ensure that the data path is isolated and isolated data.
At present, mainstream manufacturers such as TI and ADI have launched high-performance products in this category.

TI AMC series isolated ADC
AMC1106M05 has ±50mV input and CMOS interface. The output and input circuit of this isolated ADC are separated by a capacitive isolation layer with strong anti-electromagnetic interference performance.
The input stage of this series is optimized for direct connection to shunt resistors or other low-voltage signal sources. It performs very well in AC and DC performance and is usually used in multi-phase fuel gauges. In the low input voltage range, shunt resistors with smaller resistance values ​​are used to minimize power dissipation. Excellent DC performance brings high accuracy, and this series of products has minimal offset and gain errors. The offset error is only ±50 µV, and the gain error is ±0.2%.
The AMC1303 is a series of high-precision delta-sigma modulators with internal clocks. The output and input circuits of this isolated ADC are also separated by a capacitive double isolation layer with strong anti-electromagnetic interference performance. Different from the previous series, the isolation layer is certified and can provide reinforced isolation up to 7000 VPK in accordance with the standard. When used in combination with an isolated power supply, the isolated modulator can isolate the components of the system operating at different common-mode voltage levels and prevent damage to lower voltage components. The device has two clock options, 10MHz and 20MHz, and can achieve a 16-bit resolution with a dynamic range of 85dB at an effective output data rate of 78kSPS. It is widely used in industrial motor drives, photoelectric inverters, power factor correction circuits, etc.
In addition, TI also has the AMC1306 series, which is somewhat similar to the 1303 series, but adds a CMOS interface and has a high CMTI.

ADI series isolated ADC
Based on ADI’s iCoupler technology, the ADuM7704 can convert analog input signals into high-speed unit data streams through the on-chip digital isolation function. The analog input is continuously sampled by a high-performance analog modulator and converted into a 1-density digital output stream with a data rate of up to 21 MHz. Using a suitable sinc3 digital filter to reconstruct the original information, a signal-to-noise ratio of 86 dB can be achieved at 78.1 kSPS with a decimation rate of 256 and a master clock of 20 MHz. This series of serial interfaces uses digital isolation, high-speed complementary metal oxide semiconductor (CMOS) technology and integral transformer technology to achieve on-chip isolation, so it can provide better performance than alternatives such as optocoupler kits Features.
ADE7912 is an isolated 3-channel Σ-Δ ADC, which can be used in devices such as shunt-based three-phase electric meters, power quality monitoring, and solar inverters. Data and power isolation are still ADI’s iCoupler technology. The ADE7912 integrates two 24-bit ADCs. The current ADC can provide a 67 dB signal-to-noise ratio within a 3 kHz signal bandwidth, while the voltage ADC can provide a 72 dB signal-to-noise ratio within the same bandwidth. The iCoupler chip-level technology can also isolate the logic signals between the first and second stages of the ADC. Therefore, the isolated ADC based on iCoupler can achieve small size and complete isolation, which has a significant performance enhancement, and the service life of the device is also Significantly extended.

There is not much difference in essence between isolated ADC and ordinary ADC. Ordinary ADCs can also be isolated from the main circuit by optical couplings or digital isolators, and isolated ADCs have all of this in the chip. Different isolation schemes and isolation technologies will have a huge impact on ADC performance. Data isolation has little effect on the overall system, while the choice of clock and power isolation technology has a direct effect on device performance.

Popular ic chip you may need:
PM25RSK120 
PN4393 
TDA1514A 
RFP40N10