Due to the extremely narrow single pulses of a laser distance measurer —with the transmitting pulse width only several nanoseconds and the receiving pulse width at most about 20 nanoseconds—the sampling rate requirement for the analog-to-digital converter (ADC) is extremely high, which increases the difficulty of digitization. Since the analog signal converter can only detect the echo signal of a single pulse, it is difficult to handle constant false alarm rate (CFAR) and cannot make full use of the information between pulses. Therefore, the pulse signal receiver can only work under the condition of high frequency stability, typically about 9~10, significantly reducing the detection distance of the laser rangefinder. Thus, how to improve the measurement distance and ranging accuracy of laser distance measurer has become a key challenge being addressed in the current society.
At present, laser distance measurer with high-speed digitization and fast DSP (Digital Signal Processing) capabilities have passed laboratory tests and field trials, meeting the required performance parameters and greatly extending their operational range. The hardware composition of a digital laser rangefinder can be roughly divided into three parts:
- A 500 MHz high-speed ADC (analog-to-digital converter).
2. A digital signal processing (DSP) module.
3. Various communication interfaces.
Analog laser distance measurer can only detect the echo of a single laser pulse, using a voltage comparison method. A threshold voltage is first set: if the echo voltage exceeds the threshold, a target is identified; otherwise, it is not. In contrast, digital laser distance measurer can not only perform pulse detection but also facilitate multi-pulse detection. When detecting targets for a single laser echo signal, digital rangefinders can perform processed such as matched filtering and CFAR (constant false alarm rate) detection on the echo signal, improving the frequency stability and detection accuracy of the echo. This allows maximizing the detection probability under a certain false alarm probability. Meanwhile, digital laser distance measurer can also perform data processing such as correlation detection, feature matching, and matching tracking.
