An integrated receiver–time-to-digital converter (TDC) chip set is developed for pulsed time-of-flight (TOF) laser rangefinding. The receiver detects the current pulse from the optical detector and produces a timing mark for the TDC. The receiver uses time mode walk error compensation scheme achieving $\mu \text{m}$ complementary metal–oxide–semiconductor (CMOS) technology. The functionality of the chip set was demonstrated in a laser radar platform using 12 W and 3-ns optical pulses produced by a laser diode (LD). Measurement accuracy of ~ ±3 mm was achieved with noncooperative targets at a distance range of a few tens of meters within an amplitude range of received echoes of 1:40 000.

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A CMOS Receiver–TDC Chip Set for Accurate Pulsed TOF Laser Ranging

An analog front-end (AFE) circuit comprising an amplifier module, a peak detector, and a timing discriminator has been designed to facilitate the target identification for direct time-of-flight (dToF) LiDAR. The amplitude saturation error (ASE) is compensated in this article for the intensity determination, which is conducted based on the combination of the pulse width and peak detector. Together with the improved walk error compensation scheme, the proposed AFE circuit can attain the distance and intensity information simultaneously with lower cost and larger dynamic range. A specific frequency compensation method is proposed with a shunt feedback TIA, which improves the stability and mitigates the impact of the package parasitics. The measured -3-dB bandwidth, transimpedance gain, and the input-referred noise current are 281 MHz, 86 dB $\Omega $ , and 4.68 pA/ $\surd $ Hz respectively. The proposed AFE circuit, which is fabricated in $0.18~\mu \text{m}$ CMOS technology, achieves the distance accuracy of ±30 ps and the intensity accuracy of ±4% in the dynamic range of 1:5000 without gain control scheme.

A Low Walk Error Analog Front-End Circuit With Intensity Compensation for Direct ToF LiDAR

This paper presents a linear-mode light detection and ranging (LiDAR) analog front-end architecture with multiplex analog-to-digital converter/time-to-digital converter (ADC/TDC). An added voltage-to-time converter (VTC) and a reused TDC are simultaneously used to implement the ADC and TDC function, thus replacing discrete ADC and TDC, saving hardware cost and reducing power consumption. A three-stage inverter-based transimpedance amplifier (TIA) with ultra-low-power, low-noise and high/low gain mode (long/short range mode) is proposed to reduce its influence to optical signal-to-noise ratios (OSNR). The prototype TIA and ADC/TDC is fabricated in the 65-nm CMOS technology and integrated into the single-line APD-based LiDAR system. The receiver front-end of TIA and ADC/TDC only consumes 12.44-mW. The minimum detection current of the receiver front-end is less than 238 nA with bandwidth of 150MHz for long-range and weak-light detection. LiDAR achieves a measurement range of 60 m with a 70-klx direct sunlight and only 6.16 mW average laser power. Experimental results show that this architecture is suitable for low-cost multi-line integrated LiDAR applications compared to conventional architecture using ADC, TDC, ADC+TDC architecture.

A 60-m Range 6.16-mW Laser-Power Linear-Mode LiDAR System With Multiplex ADC/TDC in 65-nm CMOS

This paper presents a Time-of-Flight laser radar receiver based on pulse-shaping at the input to the receiver channel, in which the first zero-crossing point of the converted pulse is marked as the timing moment. In this technique, an LC resonator is combined with a nonlinear feedback TIA to achieve high accuracy and high precision within a wide dynamic range. The key advantage is that the receiver does not require any post compensation or gain control techniques so that the total complexity of the TOF radar is reduced considerably. Measurements made in a $0.35~\mu m$ standard CMOS process show a bandwidth of $230MHz$ and an input-referred noise of $70nA$ RMS. The receiver chip consumes $155mW$ power from a $3.3V$ supply. The single-shot precision and accuracy of the receiver within a dynamic range of 1:50,000 are $ \sim 15mm(SNR=12)$ and $\sim \pm 15mm$ respectively. A wider dynamic range can be achieved with a larger accuracy tolerance. The functionality of the proposed receiver channel is also verified over an input pulse variation and temperature range of $0~^{\mathrm {o}}\text{C}$ to $50~^{\mathrm {o}}\text{C}$ .

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A Wide Dynamic Range Laser Radar Receiver Based on Input Pulse-Shaping Techniques

A linear-array receiver analog front-end (AFE) circuit, which mainly consists of 16 transimpedance amplifiers (TIAs), is presented for pulsed time-of-flight (TOF) rotating scanner light detection and ranging (LiDAR) application. In particular, a single-channel TIA with a novel cascaded combination consists of a transimpedance preamplifier biased by a power supply of 1.8 V, a post amplifier (PA), and an output buffer (OB) with a 3.3-V power supply, aiming to lower the parasitic capacitance of the input stage and widen the output swing range, respectively. Meanwhile, the input-referred noise current is investigated to evaluate the detecting capability for the weak pulse current, and the crosstalk reduction schemes in circuit design and layout design are presented for the proposed AFE circuit. The proposed AFE circuit, which achieves a high gain of 100 dB ${\Omega }$ , a low gain of 60 dB ${\Omega }$ , a simulated transimpedance gain bandwidth of approximately 450 MHz, an equivalent input-referred noise current of 2.59 pA/Hz0.5, a signal-to-crosstalk ratio of 40.1 dB between adjacent channels, and a minimum detectable signal of $2.5~{\mu }\text{A}$ at SNR = 5, was fabricated in a 0.18- ${\mu }\text{m}$ standard CMOS technology. The total area of AFE circuit, which includes the circuit core, bandgap and bias circuits, and I/O PAD, is approximately equal to ${4.80}\times {0.85}$ mm2.

A Linear-Array Receiver Analog Front-End Circuit for Rotating Scanner LiDAR Application

This paper presents a linear-mode optical sensor for the feasible applications of unmanned vehicle LiDAR systems, in which a pulsed-erbium fiber laser is exploited as a light source and a 16-channel transimpedance amplifier (TIA) array is utilized in an optical Rx module with low-cost InGaAs PIN photodiodes. In particular, a voltage-mode CMOS feedforward (VCF-TIA) is newly proposed to achieve twice higher transimpedance gain with lower noise and similar bandwidth characteristics than a conventional inverter TIA, thereby enabling longer detection. Test chips of the 16-channel VCF-TIA array realized in a standard 0.18- $\mu \text{m}$ CMOS process demonstrate 76.3-dB $\Omega $ transimpedance gain, 6.3-pA/sqrt(Hz) average noise current spectral density, less than −33-dB crosstalk between channels, and 29.8-mW power dissipation per channel from a single 1.8-V supply. Automatic gain control is also equipped to extend input dynamic range for near-range detection. Hence, the proposed linear-mode optical sensor clearly detects the reflected optical pulses from the target of 5% reflection rate within the range of 0.5–25 m.

A Linear-Mode LiDAR Sensor Using a Multi-Channel CMOS Transimpedance Amplifier Array

A portable system for fluorescence measurement has been developed for cyanobacteria detection. Exploiting commercially available low-cost photodiodes and a single 9 V supply, the system was able to measure two fluorescence emissions simultaneously. Output voltages resulting from the fluorescence intensity were measured by utilizing two quantum dots of QD565 and QD655. These quantum dots were employed into a NanoGene assay for mcyD gene (synthetase of toxic microcystin) detection of Microcystis aeruginosa. We investigated various operational parameters (e.g., distance, angle between laser emission and sample, and so on) for the proposed system. Measurements indicated the highest output voltage signal was obtained at a distance of 0.5 cm with the right angle (90°) between the laser source and a sample vial. Also, the mcyD gene hybridized with QD565 and QD655 was quantitatively detected by the proposed detection system, i.e., the normalized output voltage (QD655/QD565) was linearly proportional to the mcyD gene copy numbers (y = 0.41 log $x +6.6$ , $\text{r}^{2} =0.92$ ). Finally, the quantitative data were transferred wirelessly to the readout via Bluetooth.

Seung-Hoon Kim

Papers

A Linear-Mode LiDAR Sensor Using a Multi-Channel CMOS Transimpedance Amplifier Array

Portable Fluorometer for Cyanobacteria Detection