Replacement of ADS1294 with GXSC AFE Hardware and Software for Near-Infrared Brain Imaging Systems

Functional near-infrared spectroscopy (fNIRS) is a non-invasive brain functional detection technology that offers advantages such as radiation-free operation, immunity to electromagnetic interference, dynamic monitoring capabilities, and suitability for detecting movement. This brain imaging system relies on high-precision acquisition of weak photovoltage signals. The blood oxygen feedback signals output by photodetectors have extremely low amplitude, are noise-sensitive, and exhibit strong multi-channel temporal correlation, placing high demands on the acquisition chip’s channel synchronization, input impedance, and noise suppression capabilities.

GXSC’s analog front-end (AFE) chip features 24-bit high precision, four-channel synchronous acquisition, and a built-in programmable gain amplifier with flexible gain adjustment, making it highly suitable for near-infrared brain imaging systems. The GXSC AFE’s performance is comparable to that of the ADS1294, allowing for direct pin-to-pin replacement without requiring hardware or software modifications, thereby reducing development costs.

Designed specifically for EEG applications, the GXSC AFE features functions such as respiration detection, right leg drive, lead disconnection detection, pacing detection, and WCT. It supports switching to an internal clock and internal reference, thereby simplifying peripheral circuitry and significantly reducing the size, power consumption, and cost of the application product.

The GXSC AFE features a built-in programmable gain amplifier, an internal reference, and a built-in oscillator. By configuring the multiplexer to select the signal connected to the ADC’s main channel, it enables offset testing, temperature monitoring, power supply measurement, and channel testing, facilitating easier monitoring of the chip and product’s operating environment. Its key features are as follows:

• Data rate: 31.25 SPS to 32 kSPS

• Programmable gain: 1, 2, 3, 4, 6, 8, or 12

• Ultra-low input reference noise: 4.07 μVpp (0.64 μVrms) (BW = 150 Hz, G = 6)

• CMRR: 120 dB

• Flexible power modes: High-Speed (HS), Low-Power (LP), Ultra-Low-Power (ULP)

• Low-power mode with power consumption as low as 410 µW (AVDD = 3 V, DVDD = 1.8 V, ODR = 500 SPS, G = 6)

• Integrated low-drift reference; integrated clock with adjustable frequency and external output capability

• Integrated right-lead drive amplifier, lead disconnection detection, temperature sensor, and test signal

• Supports digital pacing detection

• Adjustable data buffer depth (1/2/4/8/16/32)

• Offset/gain error calibration

• Supply voltage range: Analog supply: 2.7V to 5.25V; Digital supply: 1.8V to 5.25V

• Flexible power-down and standby modes

• SPI interface

• Operating temperature range: -40°C to +85°C