Laser Driver Circuit With Analog Mixer for Wider PLL Lock Range
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Solution Overview
Problem
Conventional phase locked loop (PLL) systems in LIDAR technology face limitations in locking range due to the fundamental lower limit of supported reference frequencies based on loop bandwidth, which restricts the ability to sense both distance and speed effectively in coherent LIDAR techniques like FMCW radar.
Innovation Solution
The implementation of an analog multiplier and offset voltage combiner circuitry replaces traditional phase frequency detector (PFD) circuitry, allowing for lower reference frequencies and enabling the PLL to lock over a broader range by providing a majority of the necessary control offset, thereby removing the locking range limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional phase frequency detector (PFD) circuitry is used in the PLL, then the circuit structure is simple, but the locking range is limited due to the fundamental lower limit of supported reference frequencies based on loop bandwidth
Solution Approach 1:
The patent changes the fundamental parameters of the PLL by replacing the PFD with a mixer and adding an offset voltage source. This parameter change enables the system to support lower reference frequencies and achieve a broader locking range, directly resolving the contradiction between adaptability and complexity.
Solution Approach 2:
The offset voltage source acts as an intermediary element that provides a DC offset to the mixer output. This intermediary component enables the PLL to lock over a broader frequency range by shifting the operating point, allowing the system to achieve extended adaptability without excessive complexity.
2Adaptability or versatility
If the PLL loop bandwidth is reduced to support lower reference frequencies, then the locking range increases, but the lock time increases proportionally
Solution Approach 1:
The patent segments the frequency control function by separating the mixing operation from the phase detection function. The mixer handles the frequency conversion while the offset voltage provides the necessary frequency shift, allowing independent optimization of loop bandwidth and lock time characteristics.
Solution Approach 2:
The system dynamically adjusts the offset voltage to maintain optimal locking conditions across different reference frequencies. This dynamic adjustment allows the PLL to achieve broad frequency coverage while maintaining reasonable lock times by adapting to different operating conditions.
3Adaptability or versatility
If the mixer circuitry must cover the entire frequency range by itself, then the circuit structure remains simple, but the locking range is constrained by the loop bandwidth
Solution Approach 1:
The patent merges the mixing function with the frequency control function by combining the mixer output with an offset voltage source. This merging creates a unified frequency control mechanism that achieves broader locking range while maintaining circuit simplicity through functional integration.
Solution Approach 2:
The offset voltage source serves multiple functions: it provides frequency shifting, extends the locking range, and enables the system to support lower reference frequencies. This multi-functionality resolves the contradiction by achieving enhanced adaptability without proportionally increasing circuit complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the LIDAR system's ability to accurately measure range and velocity by stabilizing the PLL and extending its locking range, allowing for more precise spatial awareness and real-time measurements.
Implementation Method 1
mixer circuitry that calculates a difference value between the beat frequency and a reference frequency
Implementation Method 2
The laser diode generates optical energy at a wavelength that is proportional to the magnitude of the current through the laser diode. As such, modulating the current modulates the frequency of the optical energy and generates the chirps.
Implementation Method 3
a receiver that captures at least a portion of the optical beam and generates a beat frequency based on the chirp rate
Data Source
AI summary
A frequency-modulated continuous-wave (FMCW) light detection and ranging (LIDAR) system includes an optical source to generate an optical beam at a chirp rate based on a control signal. The system includes a receiver to capture at least a portion of the optical beam and generate a beat frequency based on the chirp rate. The system also includes mixer circuitry to calculate a difference value between the beat frequency and a reference frequency. The system also includes combination circuitry to combine the difference value with an offset voltage to generate an adjusted control signal that is configured to minimize the difference value to maintain the chirp rate.