[Prize-winning quiz] A new generation of intelligent gas detection solutions

[Figure 1 ADUCM355 on-chip architecture]

[Figure 2 ADuCM355 AFE DIE ≈ AD5940/1]

As shown in Figure 1, the structural architecture of ADuCM355 is actually a technical architecture of = two DIE packages, DIE1≈analog front end AD5940/1, DIE2=MCU=ADUCM3029.

As shown in Figure 2, the functional block diagram architecture of the ADuCM355 AFE is the same as that of the AD594X. However, the ADuCM355 has more analog resources than the AD594X.

ADuCM355 AFE Analog Front End

• LOWBANDWIDTH LOOP Low Bandwidth Loop

• Two dual-channel output voltage DACs

• Two low power, low noise amplifiers (AD594X = 1)

• Two low power, low noise TIAs (AD594X = 1)

• Programmable load and gain resistors

• HIGHBANDWIDTH LOOP High bandwidth loop

• 1 high-speed 12-bit voltage DAC

• 1 high-speed TIA for impedance measurements

• Programmable gain amplifier on output

• Impedance measurement range: <1 Ω to 10 MΩ, 0.016 Hz to 200,000 Hz

• Analog Input/Output

• 16-Bit, 400 kSPS ADC Voltage

• Internal and external current and voltage channels

• Ultra-Low Leakage Switch Matrix and Input Multiplexer

• Input Buffer, PGA

• 2.5 V and 1.82 V on-chip precision voltage references

• Simulation Hardware Accelerator

• Digital Waveform Generator

• DFT and Digital Filters

• Internal temperature sensor, ±2°C accuracy

microprocessor

• 26 MHz Arm Cortex-M3 processor

• Serial line port supports code download and debugging

• 128 kB Flash/64 kB SRAM

• UART, I2C and SPI serial input/output

• Up to 17 GPIO pins

• General purpose, wake-up and watchdog timers

ADuCM355 Gas Detection SOC Solution Advantages

1. High integration - reducing signal chain design complexity

[Figure 3 Typical traditional electrochemical gas detection signal chain]

[Figure 4 ADuCM355 electrochemical gas sensing signal chain]

Through understanding the internal architecture of ADuCM355 and the comparison between traditional electrochemical gas detection solutions and ADuCM355 solutions in Figures 3 and 4, the advantages of ADuCM355 solutions are: highly integrated and digital. Ethan introduced that Shijian Company had promotion and communication with engineers from a well-known portable environmental protection enterprise in Shandong in the early stage, and high integration was the most important factor in their evaluation of introducing ADuCM355 solutions.

2. Ultra-low power consumption

[ Figure 5 Low bandwidth loop maintains the bias voltage of the EC reference electrode]

For example, in a common three-electrode electrochemical sensor, according to the working principle of the electrochemical sensor, the 12-bit VDAC output sets the voltage on the reference electrode pin through the potentiostat circuit shown in Figure 5. The voltage on the CE pin and the RE pin is called VBIAS. The 6-bit output sets the bias voltage on the LPTIA_P node; this output sets the voltage on the sensing electrode pin SE. This voltage is called VZERO. The VBIAS bias voltage on the sensor is actually the difference between the 12-bit output and the 6-bit output. In low-power mode, in the non-measurement state BIAS mode connected to a low-bandwidth loop sensor, this system circuit can achieve ultra-low power consumption of 8uA. The sensor is 4.9mA when working and measuring.

3. High measurement accuracy

[Figure 6 ADC ENOB, based on RMS noise]

The electrochemical sensor is connected to the ADuCM355 low-bandwidth loop, and the output of a very small current is converted into a voltage signal that can be measured by the ADC through low power consumption (LPTIA TIA supports programmable gain resistors from 200Ω to 512kΩ). The 16BIT high-resolution SAR ADC, with an internal high-precision 20ppm 1.82Vref as the ADC reference source and a programmable digital filter, can achieve an acquisition accuracy of up to 15BIT effective bits as shown in Figure 6.

4. Diagnostic and predictive type - electrochemical impedance spectroscopy analysis

【Figure 7 High Bandwidth Loop High Bandwidth Loop Ratio Method to Measure EC Impedance】

As electrochemical applications develop, it is of great value to perform diagnostic measurements. Electrochemical impedance spectroscopy analysis is shown in Figure 7. The ADuCM355 high-bandwidth loop HPDAC output frequency can reach up to 200Khz AC signal excitation sensor, combined with the complex impedance measurement (DFT) engine, can help customers effectively diagnose the health status of the sensor.

For some types of sensors, the DC bias on the sensor must be maintained during the impedance measurement. The level of the AC signal is set by the VBIAS voltage output of the low power DAC, and the voltage on the SE is maintained by the VZERO voltage. The high speed DAC DC buffer must also be enabled by setting AFECON Bit 21.

ADuCM355 Design and Development Environment

[Figure 8 Hardware connection, support for electrochemical sensors]

IAR software development and debugging environment, ADI can provide a full set of ADuCM355 reference code. As shown in Figure 10, 355_ECSns_2E code can be directly burned for evaluation, combined with the hardware reference manual, and personalized development can be performed according to actual needs.

[Figure 10 ADI ADuCM355 reference code resources]