Optical Pickup TIA Circuit for Background Signal Cancellation
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Solution Overview
Problem
Existing photodetector systems struggle to accurately detect optical input signals in the presence of undesirable background optical energy, which interferes with the desired input signal and degrades system performance.
Innovation Solution
A circuit configuration using a pair of series-connected photodetectors and an operational amplifier configured as a transimpedance amplifier (TIA) to negate unwanted background optical energy before it reaches the primary detection circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodetectors are used to detect optical input signals, then optical signal detection capability is provided, but background optical energy interferes with the desired input signal and degrades detection accuracy
Solution Approach 1:
The photodetector system is segmented into multiple photodetector elements (first photodetector and second photodetector) connected in series. Each element processes a portion of the optical signal, allowing the circuit to differentiate between desired signals and background energy through differential processing, thereby improving detection accuracy in the presence of background interference.
Solution Approach 2:
A transimpedance amplifier (TIA) is introduced as an intermediary component between the photodetector elements and the output circuit. The TIA converts the current signals from the photodetectors into voltage signals and provides signal conditioning, enabling effective cancellation of background optical energy while preserving the desired input signal characteristics.
2Adaptability or versatility
If photodetectors receive broad optical bandwidth, then detection versatility is improved, but background optical energy within the bandwidth increases and interferes with signal detection
Solution Approach 1:
The photodetector system uses multiple photodetector elements connected in series, where the first photodetector responds to a first range of optical wavelengths and the second photodetector responds to a second range. This segmentation allows the system to maintain broad bandwidth versatility while differentiating between desired signals and background energy through differential processing.
Solution Approach 2:
Different photodetector elements are assigned different spectral response characteristics (first photodetector for first wavelength range, second photodetector for second wavelength range). This local quality differentiation enables the system to selectively detect desired optical signals while rejecting background energy in specific wavelength bands.
3Object-affected harmful factors
If tight bandpass optical filtering is applied to reduce background energy, then background signal rejection is improved, but detection of desired input signals over wavelength ranges becomes difficult
Solution Approach 1:
Instead of using tight bandpass filters that would limit wavelength range detection, the system segments the photodetector elements to have different spectral responses. The first photodetector detects signals in a first wavelength range while the second photodetector detects signals in a second wavelength range, allowing broad wavelength detection without requiring restrictive filtering.
Solution Approach 2:
The system changes the spectral response parameters of different photodetector elements to match the characteristics of desired input signals. By adjusting which photodetector responds to which wavelength range, the system can adapt to different detection requirements without using tight bandpass filters, thus maintaining both background rejection and wavelength versatility.
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
Effectively cancels background optical signals, preventing debiasing of photodetectors and maintaining accurate detection of desired input signals, even in environments with significant background energy.
Implementation Method 1
Photodetectors in optical detection systems are typically configured to receive an optical input signal within the optical bandwidth of the sensor and generate an electrical output that is proportional to the power of the input signal
Implementation Method 2
circuitry comprising a plurality of in-series photodetector elements electrically coupled to, for instance, an operational amplifier (op-amp) that may be configured as a transimpedance amplifier (TIA)
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
An optical sensor circuit for improved background signal cancellation in a musical instrument pickup. An operational amplifier is configured as a transimpedance amplifier (TIA). The TIA is electrically coupled to a first photodetector and a second photodetector in a series connection wherein the anode of the first photodetector and the cathode of the second photodetector are electrically coupled to define a connection node that is electrically coupled to an input of the TIA. In this configuration, symmetric in-band and out-of-band background optical signals and symmetric DC signals received by the pickup are negated. Asymmetric non-DC signals that are output from the photodetectors are passed to the input of the TIA as a signal of interest generated at the connection node.