## 3 Chip Layout and Post-Layout Simulation Results  
The post-layout simulations were performed by using the parameters of a standard 180 nm CMOS technology with the simulation software 'Cadence 6.1.6 Spectre'. During these simulations, the on-chip APDs were modeled as equivalent electrical lumped elements, incorporating a series resistance of 25 \(\Omega\) and a parasitic capacitance of 490 fF. Figure 7 shows the layout of the proposed LiDAR receiver, which includes two integrated on-chip P\({}^{+}\)/NW/DNW APDs and covers a core area of 200 \(\times\) 120 \(\upmu\)m\({}^{2}\). The DC simulations reveal that the whole receiver dissipates 6 mW power consumption from a single 1.8 V supply. Figure 8a shows the simulated frequency responses of the proposed OTA, achieving a transimpedance gain of 67 dB\(\Omega\), a bandwidth of 830 MHz, and an average noise current  
Figure 6: (**a**) A block diagram of T2V converter and (**b**) a schematic diagram of latch comparator. Figure 7: Layout of proposed LiDAR receiver. spectral density of 16 pA/\(\sqrt{\mathrm{Hz}}\) that corresponds to an optical sensitivity of \(-\)31 dBm for a \(10^{-12}\) bit error rate (BER), with the assumption of 4.16 A/W APD responsivity [17]. Figure 8b depicts the gain variation in the OTA by the action of the proposed concurrent AGC circuit, hence turning on the switches in the m-TIA by the output voltages of the replica TIA. These results prove the functionality of the concurrent AGC to maintain consistent gains across a wide range of input current levels. Figure 9 depicts the simulated pulse response of the OTA, in which the input currents vary within the range from 1 \(\mu\)A\({}_{\mathrm{PP}}\) to 5.5 mA\({}_{\mathrm{PP}}\), and the corresponding output voltages are observed with negligible distortions. Also, it can be clearly seen that the amplitudes of the output voltages change almost linearly for input currents from 1 \(\mu\)A\({}_{\mathrm{PP}}\) to 200 \(\mu\)A\({}_{\mathrm{PP}}\), and then the output voltages remain constant at \(\sim\)500 mV\({}_{\mathrm{PP}}\) for input currents beyond 200 \(\mu\)A\({}_{\mathrm{PP}}\). Although the output voltage signals evidently exhibit distortions for input currents larger than 4 mA\({}_{\mathrm{PP}}\), these slight distortions can be effectively eliminated by subsequently exploiting the T2V converter (shown below in Figure 10). The above results confirm the tester abilities of the A2V and T2V converters for short-range LiDAR sensors. The A2V converter detects the difference in the amplitudes and is suitable for signals reflected from relatively longer distances that correspond to small input currents. Conversely, the T2V converter measures the time interval between the START and STOP signals and is adequate for short-range detection. In other words, particularly in the pulse simulations, the A2V converter is effective in the linear region, while the T2V converter is applicable in the region where the amplitudes can be saturated. Figure 8: (**a**) The simulated frequency response of the proposed OTA and (**b**) the gain variation with the proposed concurrent AGC. Figure 9: Simulated pulse response of the proposed OTA for the different input currents. Figure 10a shows the simulated transient response of the A2V converter with variations in the input currents ranging from 5 \(\mu\)A\({}_{\text{PP}}\) to 200 \(\mu\)A\({}_{\text{PP}}\), where the voltages converted by the m-TIA pass through the PA (in gray) and subsequently the PDH (represented in color). The relationship between the target distance (\(x\)) and the incoming photocurrent (\(ip_{D}\)) is given by  
\[x=\frac{1}{2}\sqrt{\frac{R\times P_{OPT,TX}}{ip_{D}}},\]  
where \(R\) is the responsivity of the on-chip APD, and \(P_{\text{3 dB}}\) is the transmitted optical power, with the assumption of 0 dBm (i.e., 1 mW).