# A Current-Mode Optoelectronic Receiver IC for Short-Range LiDAR Sensors in 180 nm CMOS
## 3 Voltage-Mode Optoelectronic Receiver (V-OER)
### Measured Results  
Firstly, the implemented V-OER IC demonstrated the electrically measured eye-diagrams, where the eyes of the V-OER IC were wide and clean at a data rate up to 500 Mb/s with the input currents of 20 \(\mu\)A\({}_{\text{PP}}\) and 50 \(\mu\)A\({}_{\text{PP}}\), respectively. The single-ended output amplitude of each eye-diagram was measured with a 50 \(\Omega\) termination, where amplitudes acquired were similar to those demonstrated in [5]. Secondly, the electrically measured output noise of the V-OER IC revealed that the equivalent noise current spectral density was 4.54 pA/\(\sqrt{\text{Hz}}\), which corresponds to the optical sensitivity of \(-\)35.5 dBm for the BER of \(10^{-12}\) with the APD responsivity of 2.77 A/W. Here, it is noted that the inherent noise voltage of the utilized oscilloscope (i.e., Agilent DCA 86100D) was measured to be 0.75 mV\({}_{\text{RMS}}\). Figure 9 depicts a PC-board module for optical testing, in which on-chip APDs were integrated on the same die of the V-OER IC. The four-channel V-OER array IC occupies the total area of 2.0 \(\times\) 1.1 mm\({}^{2}\), including I/O pads. For optical testing, an 850 nm laser source driver (Seed LDD, Notice Korea Ltd., Anyang, Republic of Korea) with a laser diode (Qphotonics, Ann Arbor, MI, USA) was utilized to generate light pulses. Figure 10 demonstrates the electrically measured eye-diagrams of the V-OER at 500 Mb/s with different input currents of 20 \(\mu\)A\({}_{\text{PP}}\) and 50 \(\mu\)A\({}_{\text{PP}}\), in which a singled-ended output was measured with a 50 \(\Omega\) termination. Hence, each output corresponds to the transimpedance gain of 91.6 dB\(\Omega\) and 85.2 dB\(\Omega\), respectively. Additionally, the output noise voltage of the V-OER IC was measured with the inherent background noise of the oscilloscope (Agilent DCA 86100D). Thereby, the input-referred average noise current spectral density is estimated to 4.54 pA/\(\sqrt{\text{Hz}}\), which corresponds to the optical sensitivity of \(-\)29.5 dBm for bit-error-rate (BER) of \(10^{-12}\) to satisfy the maximum signal-to-noise ratio (SNR) of 14. Figure 11 demonstrates the optically measured pulse responses, where the light pulses were generated by utilizing an 850 nm laser source driver. It is clearly seen that the V-OER IC with the P\({}^{+}\)/NW/DNW APD yields the largest output pulses. Figure 9: Chip photo of the V-OER IC in a test module with three CMOS APDs. Table 1 compares the performance of the realized V-OER IC with the prior parts for the applications of short-range LiDAR sensors. Ref. [4] demonstrated an optoelectronic receiver IC for home-monitoring purposes, which consisted of an on-chip P\({}^{+}\)/NW APD, a feedforward TIA, and a limiting amplifier. However, the measured results showed poorly recovered optical pulses, i.e., 8 mV\({}_{\mathrm{pp}}\) amplitude with a 25 ms pulse width. Ref. [11] suggested a differential shunt-feedback (SF) TIA employing an off-chip APD (with 40-A/W responsivity). Even though it achieved very high transimpedance gain and a very large maximum detectable input current, AC coupling capacitors and bias resistors were mandatory for the interconnection between the off-chip APD and the receiver. Additionally, it required a separate TDC IC so that the maximum input dynamic range could be achieved. Ref. [12] presented a frequency-compensated inverter TIA that could demonstrate very-low-noise current spectral density. However, it revealed high power dissipation and mandated a large reverse voltage of 200 V for the off-chip APD to achieve 50 A/W responsivity characteristics. Ref. [13] realized a shunt-feedback (SF) TIA with an off-chip APD, providing a very low-power solution. Furthermore, it could recover a narrow pulse width of 2 ns. Yet, the chip area was quite large. The V-OER IC exploits an on-chip APD to realize a small chip area and provide a low minimum detectable current and a large signal-to-noise ratio (~10 in this work).