Digital Gain Control for Laser Barcode Scanners
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Solution Overview
Problem
Conventional laser scanning bar code symbol readers face challenges in maintaining fast response time and signal linearity, especially at long ranges, due to limitations in automatic gain control (AGC) circuits which sacrifice response time for linearity and vice versa.
Innovation Solution
A synchronized digital gain control (SDGC) module is introduced, using start of scan (SOS) signals to synchronize gain adjustments in analog signal processing stages, allowing discrete gain changes only during specific time windows, thereby maintaining signal linearity while enhancing response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional automatic gain control (AGC) circuits are used to control gain in analog signal processing stages, then signal linearity is maintained, but response time is slowed down
Solution Approach 1:
The patent replaces conventional analog AGC circuits with a digital gain control system. A processor determines the gain required for the current scanning cycle and stores it in memory. During scanning, the laser beam reads the barcode, and the stored gain value is applied to the analog-to-digital converter to control the gain of the signal processing stage. This digital control mechanism eliminates the slow feedback loops of analog AGC while maintaining signal linearity, thereby resolving the contradiction between response time and signal linearity.
2Loss of time
If discrete gain changes are applied only during specific time windows synchronized to the scanning cycle, then response time is improved, but maintaining signal linearity becomes challenging
Solution Approach 1:
The patent implements preliminary action by determining the required gain for the current scanning cycle before the scanning begins. The processor calculates the appropriate gain value and stores it in memory in advance. When the scanning cycle starts, the stored gain value is immediately applied to the signal processing stage, ensuring both fast response time and maintained signal linearity throughout the scanning process.
Solution Approach 2:
The patent employs periodic action by synchronizing the gain control to the scanning cycle. The gain is adjusted at specific intervals corresponding to each scanning cycle, with the processor determining the gain requirement for each cycle and applying it through the analog-to-digital converter. This periodic synchronization ensures that gain changes occur at optimal moments, maintaining signal linearity while enabling fast response times between cycles.
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
The SDGC module effectively controls gain in real-time during each laser beam scanning cycle, improving signal quality and response time without sacrificing linearity, even at long scanning distances.
Implementation Method 1
collecting and processing light from the return laser beam to extract information modulated onto the scanned beam
Data Source
AI summary
A scanning code symbol reading system includes an analog scan data signal processor for producing digitized data signals, wherein during each laser beam scanning cycle, a light collection and photo-detection module generates an analog scan data signal corresponding to a laser scanned code symbol, an analog scan data signal processor/digitizer processes the analog scan data signal to generate digital data signals corresponding thereto, and a synchronized digital gain control module automatically processes the digitized data signals in response to start of scan (SOS) signals generated by a SOS detector. The synchronized digital gain control module generates digital control data which is transmitted to the analog scan data signal processor for use in controlling the gain of a signal processing stage in the light collection and photo-detection module and/or analog scan data signal processor, during the corresponding laser beam scanning cycle.