Bitstream Photon Counting Chirped AM Lidar with a Dual Unipolar Signal

Abstract

This paper is a follow-up to three previous papers: the first introducing the new Bitstream Photon Counting Chirped Amplitude Modulation (AM) Lidar (PC-CAML) with the unipolar Digital Logic Local Oscillator (DLLO) concept, the second introducing the improvement thereof using the bipolar DLLO, and the third introducing the improvement of digital In-phase and Quadrature-phase (I/Q) demodulation.In that previous work, the signal was a single unipolar chirped sinusoidal or square wave. This paper introduces a new bitstream PC-CAML transceiver architecture that combines two unipolar chirped signals, referred to as the dual unipolar signal, to form a single bipolar signal in the receiver. (patent pending) This bipolar signal is mixed with the bipolar DLLOs in the in-phase (I) digital mixing and quadrature-phase (Q) digital mixing channels for digital I/Q demodulation for improved signal-to-noise ratio (SNR) compared to that when using a single unipolar signal.The simulation results presented in this paper indicate an SNR improvement for the dual unipolar chirped sinusoidal signal bitstream PC-CAML compared to that of the unipolar chirped sinusoidal signal bitstream PC-CAML (both with bipolar DLLOs and digital I/Q demodulation) of from about 3 dB to about 6 dB for signals below the onset of receiver saturation, and an improvement for maximum achievable SNR of about 13 dB if the receiver is allowed to saturate.The bitstream PC-CAML with a dual unipolar signal and bipolar DLLOs with digital I/Q demodulation architecture discussed in this paper adds complexity to the transmitter and receiver compared to the architectures presented in the previous papers. Whether or not this additional complexity is worth the improved SNR will have to be decided as part of system trade studies for particular systems and their applications.However, the new architecture still retains the key advantages of the previous bitstream PC-CAML architectures since it still replaces bulky, power-hungry, and expensive wideband RF analog electronics in the receiver with digital components that can be implemented in inexpensive silicon complementary metal-oxide-semiconductor (CMOS) read-out integrated circuits (ROICs) to make the bitstream PC-CAML with a DLLO more suitable for compact lidar-on-a-chip systems and lidar array receivers than previous standard PC-CAML systems.This paper introduces the dual unipolar signal and bipolar DLLOs with digital I/Q demodulation transceiver architecture for bitstream PC-CAML, and presents the initial SNR theory with comparisons to Monte Carlo simulation results.