THz Down-Conversion Circuit With Photodiode DC Cancellation
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Solution Overview
Problem
Terahertz signal detection is hindered by background photocurrents generated by photodiodes, which obscure the down-conversion photocurrent, making it difficult to separate and requiring complex post-processing.
Innovation Solution
A circuit comprising two photodiodes coupled in series through a common antenna, where the optical beat signal generates a direct current component that cancels out at the output terminal, allowing only the intermediate frequency component of the down-converted THz signal to be output, eliminating the need for complex read-out circuitry and enabling easy integration into integrated circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photodiode is used for THz signal detection, then the THz signal can be down-converted to intermediate frequency, but the background photocurrent generated by the photodiode obscures the down-conversion photocurrent, making it difficult to separate the signal
Solution Approach 1:
The single photodiode is segmented into two photodiodes (first and second photodiodes) that are coupled in series through a common antenna. Each photodiode generates its own background photocurrent, but by coupling them in series with opposite polarities, the background currents cancel each other out while the down-conversion signals add up, thereby separating the signal from the noise
Solution Approach 2:
The background photocurrent, which was previously a harmful factor obscuring the signal, is converted into a beneficial element for cancellation. By using two photodiodes in series with opposite polarities, the background currents flow in opposite directions and cancel each other, while the down-conversion photocurrents from the THz signal add constructively at the output
2Measurement precision
If complex post-processing is used to separate down-conversion photocurrent from background photocurrent, then signal separation can be achieved, but the circuit complexity and cost increase
Solution Approach 1:
The harmful background photocurrent is extracted and removed at the circuit level through the series coupling configuration before the signal reaches the read-out circuitry. This eliminates the need for complex post-processing to separate the signal from the background current, as the cancellation occurs naturally in the circuit architecture
Solution Approach 2:
The circuit performs self-cancellation of the background photocurrent through its inherent series coupling configuration. The two photodiodes automatically cancel their respective background currents without requiring external intervention or complex processing circuits, thereby simplifying the overall system
3Measurement precision
If complex electronic integration is implemented to handle background photocurrent cancellation, then signal detection accuracy improves, but the integration difficulty and manufacturing cost increase
Solution Approach 1:
The two photodiodes are merged into a single integrated structure with series coupling through a common antenna and shared read-out circuitry. This merging approach achieves background current cancellation while maintaining a compact, easily manufacturable design that can be implemented as a single integrated circuit block
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 effectively cancels background photocurrents, simplifying the read-out process and allowing for a low-cost, compact, and easily integratable THz signal detection circuit that can handle both modulated and unmodulated signals, reducing the need for complex electronic integration.
Implementation Method 1
a first photodiode and a second photodiode configured to be excited by an optical beat signal, the photodiodes thereby, by means of the optical beat signal, respectively down-converting the THz signal and generating a current comprising an intermediate frequency, IF, component and a direct current, DC, component
Implementation Method 2
the antenna is configured to receive the terahertz, THz, signal; the photodiodes thereby, by means of the optical beat signal, respectively down-converting the THz signal
Data Source
Figure 1A~1B
AI summary
The present disclosure relates to a circuit for optoelectronic down-conversion of a terahertz, THz, signal, the circuit comprising: a first photodiode and a second photodiode configured to be excited by an optical beat signal, the photodiodes being coupled in series through a common antenna, wherein terminals of the antenna are coupled to form an output terminal, and wherein the antenna is configured to receive the terahertz, THz, signal; the photodiodes thereby, by means of the optical beat signal, respectively down-converting the THz signal and generating a current comprising an intermediate frequency, IF, component and a direct current, DC, component, wherein the respective generated currents are summed at the output terminal, thereby obtaining the IF components and cancelling the DC components.