Bipolar Digital Logic Local Oscillator for Bitstream Photon Counting Chirped AM Lidar

Abstract

This paper is a follow-up to a previous paper introducing the new bitstream Photon Counting Chirped Amplitude Modulation (AM) Lidar (PC-CAML) with a Digital Logic Local Oscillator (DLLO) concept. In that previous work, the DLLO was unipolar. In this paper, a new bipolar DLLO for the bitstream PC-CAML is introduced (patent pending). The bipolar DLLO retains the key advantages of the unipolar DLLO for the bitstream PC-CAML since it also replaces bulky, power-hungry, and expensive wideband RF analog electronics 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 PC-CAML systems. In addition, the bipolar DLLO improves the electrical power signal-to-noise ratio (SNR) of the bitstream PC-CAML by about 2.5 dB compared to that of the unipolar DLLO as shown by the theoretical and Monte Carlo simulation results presented in this paper. Theoretically, there should be a 3 dB improvement for the bipolar DLLO from the elimination of the signal power loss to the DC component of the intermediate frequency (IF) spectrum that occurs with the unipolar DLLO. However, this improvement is partially offset by a higher quantization noise for the bipolar DLLO compared to that of the unipolar DLLO as explained in this paper.This paper introduces the bipolar DLLO for bitstream PC-CAML concept and presents the initial signal-to-noise ratio (SNR) theory with comparisons to Monte Carlo simulation results.

Bitstream Photon Counting Chirped AM Lidar with a Dual Unipolar Signal

“…The bitstream PC-CAML with a dual unipolar signal and bipolar DLLO 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 [ref [15][16][17]. With wavelength tagging of the two channels, two sources, or one source and a wavelength shifter are required in the transmitter.…”

“…(The use of CDMA code tagging would require only one source in the transmitter, and one optical filter, one Gm-APD, and one edge-triggered pulse detector in the receiver, but it has other complexities that require investigation in future work.) Whether or not the additional complexity, which may translate to increased size, weight, power, and cost compared to the previous bitstream PC-CAML architectures [ref [15][16][17], is worth the improved SNR will have to be decided by system trade studies for particular systems and applications.…”

“…For the fully modulated unipolar chirped sinusoidal signal there is some signal everywhere except at the exact nulls of the waveform so that the speckle induced amplitude fluctuations cause photon arrival rate fluctuations at almost all points on the signal, and these fluctuations are higher for lower M causing the SNR to be lower for lower M just as seen in the Monte Carlo simulation results and theory predictions for the unipolar chirped sinusoidal signal. [ref [15][16][17] For the sake of brevity, this paper discusses only the dual unipolar chirped sinusoidal signal, whereas reference 15 discussed both the unipolar chirped sinusoidal signal and the unipolar chirped square wave signal. However, the dual unipolar signal may be either a chirped sinusoidal signal or a chirped square wave signal.…”

“…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 [ref 15], the second introducing the improvement thereof using the bipolar DLLO [ref 16], and the third introducing the improvement of digital Inphase and Quadrature-phase (I/Q) demodulation [ref 17]. Reading the previous papers [ref [15][16][17] before proceeding to read this paper is recommended.…”

“…However, the new architecure still retains the key advantages of the previous bitstream PC-CAML architectures [ref [15][16][17] 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 lidaron-a-chip systems and lidar array receivers than previous 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.…”