(A) high sensitivity and low walk error LADAR receiver for military application

Abstract

Recently, the LADAR receiver is applied in many fields such as automotive, military or ro-botics for target identification and range determination, or 2D and 3D imaging system. Pulsed time-of-flight (TOF) LADAR is widely used to measure distances due to its unique advantage of high precision compare to other measurement methods such as the continuous-wave optical phase meth-od. The pulsed TOF LADAR receiver has many design issues such as sensitivity, precision, walk error, or dynamic range. Especially for the military application which targets for km-range detection, the sensitivity of the LADAR receiver becomes a significant since the received signal is very weak due to the long distance. To deal with the weak signal, the minimum detectable signal (MDS) should be very low level around few tens of nW. The required accuracy of LADAR receiver for the military application is around a few meters. It is less precise than that of few tens of meter LADAR, however, the walk error still exists as an important issue with large dynamic range. Moreover, the multiple target resolution, power, and cost are also other issues that need to be considered in pulsed LADAR receiver. To resolve the above issues, the dissertation proposes an integrated receiver with high sensi-tivity and low walk error and corresponding TDC for a military purpose pulsed time-of-flight (TOF) LADAR system. The proposed receiver adopts a dual-gain capacitive-feedback TIA (C-TIA) in-stead of widely used resistive-feedback TIA (R-TIA) to increase the sensitivity. In addition, a new walk-error improvement circuit based on a constant-delay detection method is proposed. Imple-mented in 0.35μm CMOS technology, the receiver achieves an input-referred noise current of 1.36pA/$\surd$ Hz with bandwidth of 140MHz and minimum detectable signal (MDS) of 10nW with a 5ns pulse at SNR=3.3, maximum walk-error of 2.8ns, and a dynamic range of 1:12,000 over the operating temperature range of $-40^\circ C$ to $+85^\circ C$. Besides, a 14-bit counter-based TDC is proposed with 1.2km of measurable range with 0.5ns of resolution.