The analog-to-digital converter ADC connects the real analog world with electronic systems and has always been the crown jewel of the chip industry. With the development of technology applications, the ADC industry shows a clearer and clearer development trend. High sampling rate, high resolution and low power consumption are the future development directions. Isolated ADC, as a representative product in the ADC category, is one of the examples of ADC performance breakthrough and high integration simplifying the design burden because the isolation technology it brings enhances performance and prolongs the service life.



For an isolated high-performance ADC, the isolation technology should pay attention to isolating the clock on the one hand, and isolating the power supply on the other. The clock isolation of the ADC (sampling clock or conversion signal) is to prevent the hot end from not generating the clock, and at the same time for high performance, the clock needs to have no jitter; the isolated power supply is usually in the range of less than 10 W, and a flyback converter or push-pull converter.



In fact, there is also a data isolation, which can be achieved by digital isolators. Simply connect the SPI signals SPI Clock, SDO, SCK and Busy to the data isolator to ensure that the data path gets isolated isolated data.



At present, mainstream manufacturers such as TI and ADI have launched high-performance products in this category.



YOU AMCSeries Isolated ADCs



AMC1106

(Image source: TI)


The AMC1106M05 has a ±50mV input and CMOS interface. The output of this isolated ADC is separated from the input circuit by a capacitive isolation barrier that is extremely resistant to electromagnetic interference.



The input stages of this family are optimized for direct connection to shunt resistors or other low voltage level signal sources, and offer excellent AC and DC performance, typically used in multiphase fuel gauges. The use of smaller value shunt resistors minimizes power dissipation in the low input voltage range.



Excellent dc performance brings high accuracy, and this family has minimal offset and gain errors. The offset error is only ±50 µV, and the gain error is ±0.2%.



AMC1303

(Image source: TI)


The AMC1303 is a series of high precision delta-sigma modulators with an internal clock. The output and input circuits of this isolated ADC are also separated by a capacitive double isolation barrier that is extremely resistant to electromagnetic interference. Unlike the previous series, this isolation barrier is certified to supply up to 7000 V as standardPKreinforced isolation. When used in conjunction with an isolated power supply, the isolated modulator isolates components of a system operating at different common-mode voltage levels and prevents damage to lower voltage components.



Available in 10MHz and 20MHz clock options, the device achieves 16-bit resolution with 85dB dynamic range at an effective output data rate of 78kSPS. It has a wide range of applications 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.



ADISeries Isolated ADCs



ADuM7704

(Image source: ADI)


Based on ADI's iCoupler technology, the ADuM7704 converts analog input signals into high-speed unit data streams through on-chip digital isolation. The analog input is continuously sampled by a high-performance analog modulator and converted to a 1-density digital output stream at data rates up to 21 MHz. Reconstructing the original information with an appropriate sinc3 digital filter achieves a signal-to-noise ratio of 86 dB at 78.1 kSPS with a decimation rate of 256 and a 20 MHz master clock.



This family of serial interfaces utilizes digital isolation, high-speed complementary metal-oxide semiconductor (CMOS) technology combined with monolithic transformer technology for on-chip isolation, thus providing superior performance over alternatives such as optocoupler kits Features.



ADE7912



The ADE7912 is an isolated 3-channel sigma-delta ADC that can be used in shunt-based three-phase electricity meters, power quality monitoring, solar inverters, and more. Data and power isolation remains ADI's iCoupler technology.



The ADE7912 integrates two 24-bit ADCs, the current ADC provides 67 dB SNR over a 3 kHz signal bandwidth, and the voltage ADC provides 72 dB SNR over the same bandwidth. The iCoupler chip-level technology can also isolate the logic signal between the first stage and the second stage of the ADC, so the isolated ADC based on iCoupler can achieve small size and complete isolation. significantly prolonged.



summary



There is not much difference between an isolated ADC and a normal ADC in essence. Ordinary ADCs can also be isolated from the main circuit through opto-couplers or digital isolators, and the isolated ADCs have all done in the chip. Different isolation schemes and isolation technologies will have a huge impact on ADC performance. Data isolation has little impact on the overall system, while the choice of clock and power isolation technology has a direct impact on device performance.



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