Using AD7606B to build a high-precision data acquisition system

nemo1991

Using AD7606B to build a high-precision data acquisition system [Copy link]

 

ADI has a deep technical accumulation in the field of industrial control, and has continuously promoted technological progress in many fields including automated test equipment, scientific and environmental monitoring, industrial sensing and control, etc. For decades, ADI has continuously promoted technological progress in many fields including automated test equipment, scientific and environmental monitoring, industrial sensing and control, etc. Among ADI's many product lines, AD/DA is its most important product line. This time, I will introduce a star product launched by ADI in recent years: AD7606B.

AD7606B core performance indicators

According to the ADI official website:

The AD7606B is a 16-bit simultaneous sampling analog-to-digital data acquisition system (DAS) with 8 channels, each channel including analog input clamp protection, programmable gain amplifier (PGA), low-pass filter, 16-bit successive approximation register (SAR), and analog-to-digital converter (ADC). The AD7606B also includes flexible digital filters, low drift, 2.5 V precision reference and reference buffers to drive the ADC and flexible parallel and serial interfaces.

The AD7606B operates from a single 5 V supply and provides true bipolar input ranges of ±10 V, ±5 V, and ±2.5 V when sampling at 800 kSPS throughput on all channels. Input clamp protection withstands voltages up to ±21 V. The AD7606B has a 5 MΩ analog input impedance, resulting in a bipolar zero code of less than 20 LSB when the input signal is disconnected and connected to ground through a 10 kΩ external resistor. Because of the single supply operation, on-chip filtering, and high input impedance, no external driver op amps are required (these amplifiers require bipolar supplies). For lower throughput applications, the AD7606B flexible digital filter can be used to improve noise performance.

• 16-bit, 800 kSPS ADC (all channels)

• Input buffer with 5 MΩ analog input impedance

• Pin compatible with AD7606

• Operating temperature range: 40°C to +125°C

• 5 V single analog supply, VDRIVE supply voltage: 1.71 V to 3.6 V

• ±21 V input clamp protection with 8 kV ESD

• Additional modes available in software mode

  • Selectable analog input range per channel

    • Single-ended, bipolar: ±10 V, ±5 V, and ±2.5 V

  • System phase, offset and gain calibration per channel

  • Analog Input Open Detection Feature

  • <22 LSB open-circuit code error (RPD = 10 kΩ)

  • Self-diagnostic and monitoring features

  • CRC error checking for read/write data and registers

AD7606B peripheral circuit design

AD7606B has a very high integration level and only needs a single 5V power supply. At the same time, it integrates a reference source internally, and its temperature drift coefficient is typically 3ppm/°C and the maximum value is 10ppm/°C, which can meet the needs of conventional applications; it can also be configured to use an external reference source.

In software mode, the AD7606B has the greatest configuration flexibility, and can select functions such as input range, per-channel calibration, and oversampling. The figure below shows its typical schematic design in software mode.

It should be noted that ADI recommends placing a series resistor in front of the ADC input to protect the ADC. According to the manual in the figure below, the maximum voltage that the AD7606B can withstand is ±21 V, and the maximum current that it can withstand is 10mA. For example, if the voltage peak that the user may measure in actual use is 50V, then the minimum series resistance is (50V-21V)/10mA = 2.9k. In actual use, a larger resistance value can be selected: Although from the perspective of analog circuits, the introduction of external resistors will cause measurement errors, the error introduced by external resistors can be almost eliminated with the gain calibration supported in the AD7606B software mode. This will be introduced again later.

In addition, external resistors and capacitors can be used together to form a low-pass filter, which can be used as an anti-aliasing filter in the system.

AD7606B Software Design

AD7606B uses a 16-bit parallel data interface, which can easily handle 8-channel 800kSPS/16-bit sampling data. At the same time, it can implement CRC verification of read and write data through software, and has complete diagnostic and monitoring features.

AD7606B can be used with ARM/DSP/FPGA with parallel data interface, and ADI also provides reference code.

AD7606B Calibration Function Description

In the external circuit design section, we mentioned that AD7606B can add external resistors to the ADC analog front end to protect the ADC port, but this external resistor will introduce additional sampling errors.

AD7606B has a system gain calibration function. Specifically, by writing the external resistor value to registers 0x09~0x10, the system will automatically calibrate the sampling result.

As shown in the figure, taking the external resistance of 27k as an example, if this calibration method is not enabled, the external resistance of 27k will introduce an error of up to 170LSB; after enabling gain calibration, it can be seen that under the same external resistance, the typical value of the error introduced is only 5LSB.

fxyc87

AD7606 is a very classic synchronous AD acquisition chip. It seems to cost about 100 yuan per chip now, which is a bit expensive.

nemo1991

fxyc87 posted on 2023-10-15 21:03 AD7606 is a very classic synchronous AD acquisition chip. Now it seems to be a hundred yuan a piece, which is a bit expensive.

This is AD7606B, an upgraded version of AD7606