Zettasensing ZSPD4018LG

The ZSPD40XX generates excitation signals via LED drivers and receives/measures return signals through current inputs on the analog front end. Four independent time slot controls are available, allowing different LED drivers and analog front end parameters to be configured in different time slots.

The analog signal receive chain of the ZSPD40XX includes a current signal input port, an internal photodiode (ZSPD4001/4002 only), an analog input gate, an input bias cancellation current source, a transimpedance amplifier, an ambient light rejection circuit, and an integrator.

The analog signal receive chain is enabled by time slot control. During the active period of each time slot, the analog signal receive chain is activated according to the corresponding time slot configuration and operates in synchronization with the corresponding transmit chain (LED driver).

To reduce system power consumption, the ZSPD40XX operates in time slot mode. After each complete round of signal sampling, the chip enters sleep mode, powering down most modules until the next time slot period when it becomes active again. The ZSPD40XX's time slot period is driven by a low-speed clock; therefore, the low-speed clock must be provided first. The chip's default low-speed clock source is configured as the internal 32K oscillator — set OSC32K_EN to enable the internal 32K oscillator and provide the low-speed clock. Once the low-speed clock is running, set the OP_EN register to start the chip's time slot cycle. After OP_EN is set, the system first starts the necessary internal modules and ensures they reach a stable operating state, which takes 2ms. The system then automatically enters the active period of the first time slot.

The ZSPD40XX supports up to 4 independent time slot configurations — Time Slot A through D — each with different parameter settings to enable signal acquisition under multiple different parameter combinations. During the active period of a time slot cycle, the system activates each enabled time slot in order from Time Slot A to D. Disabled time slots are skipped, and the system proceeds directly to the next enabled time slot. After the last enabled time slot completes, the chip enters sleep mode until the next active period. The time slot period is determined by TIMESLOT_PERIOD.

• Versatile photoelectric measurement front-end integrating analog front-end, ADC, LED driver, timing control, and FIFO
• 129dB dynamic range (receive chain, single sample)
• Two differential or two reverse-biased single-ended photodiode inputs (up to four unbiased single-ended)
• High ambient light rejection performance
• 60dB dynamic ambient light rejection (DC~1KHz)
• 100uA static ambient light cancellation current
• 4 independently configurable time slots for multi-parameter synchronous measurement
• Configurable sample rate from 0.002Hz to 16kHz (single time slot)
• High-precision ADC
• Ultra-low power mode 16-bit output
• High-performance mode 24-bit output
• Multi-pulse integration mode for weak signal applications
• Multiple conversion mode with up to 24-bit effective data output
• 3 LED drivers with programmable constant-current drive, up to 240mA per channel
• Only 10μA operating current (including LED current) under typical continuous heart rate detection conditions
• Unique low-cost ECG detection circuit
• Standard I2C communication interface
• 128-byte FIFO
• Multiple package options for different applications
• WLCSP - 16 Ball (ZSPD4000): ultra-compact 1.58×1.58mm WLCSP - 16 for space-constrained devices
• QFN - 20 (ZSPD4000/ZSPD4005): standard 3×3mm QFN - 20 for ease of production
• OLGA - 20 (ZSPD4001): transparent QFN - 20 with on-chip integrated photodiode, suitable for transmission-mode applications
• OLGA - 15 (ZSPD4018): transparent QFN - 15 with on-chip integrated photodiode, suitable for earphone applications
• OLGA - 10 (ZSPD4002): dual-cavity optical LGA integrating multi-wavelength LEDs and on-chip photodiode, for space-critical applications such as smart rings
• OLGA - 13 (ZSPD4003): dual-cavity optical LGA integrating multi-wavelength LEDs and high-performance photodiode
• -40°C to 85°C wide operating temperature range
• Supply voltage: AVDD/DVDD 1.7V to 1.9V, IOVDD 1.7V to 3.6V

• Continuous heart rate monitoring/wear detection for wearable devices
• Pulse oximeter
• Single-lead ECG detection
• PTT-based blood pressure measurement
• Fire smoke alarm
• Ambient light measurement
• Gas detection