Photodiode Emulator Circuit for Optical Receiver Self-Testing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for electrically testing optical receivers only allow for adjustment of data eye opening and do not emulate the effects of photo diode capacitance or changing optical transmitter laser power, limiting comprehensive self-testing of integrated circuits with optoelectronic integration.
Innovation Solution
A photodiode emulator circuit is introduced, comprising transistors, current sources, and a capacitor, which generates differential logic signals to emulate the photodiode's effect, allowing for adjustment of current and capacitance to mimic the optical transmitter's impact on the receiver's output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If previous electrical testing techniques are used, then data eye opening adjustment is enabled, but emulation of photo diode capacitance and laser power effects is not possible
Solution Approach 1:
The patent creates a photodiode emulator circuit that copies the electrical characteristics of an actual photodiode, including its capacitance and current response to optical power changes. This allows the receiver to be tested with simulated photodiode behavior without requiring physical photodiodes or optical transmitters, enabling comprehensive self-testing while maintaining adaptability to different photodiode and laser power conditions
Solution Approach 2:
The emulator circuit allows dynamic adjustment of key parameters including photodiode capacitance values and equivalent laser power levels through controllable current sources. By changing these parameters, the testing system can simulate different operating conditions and component variations, resolving the contradiction between comprehensive testing capability and the limitations of fixed testing setups
2Reliability
If photodiode emulator circuit is added, then comprehensive self-testing is enabled, but device complexity increases
Solution Approach 1:
The photodiode emulator circuit serves multiple functions: it simulates photodiode capacitance effects, emulates laser power variations through controllable current sources, and provides test signal generation. By consolidating these multiple testing functions into a single integrated circuit block, the patent achieves comprehensive self-testing capability while minimizing the increase in overall device complexity
Solution Approach 2:
The emulator circuit acts as an intermediary between the receiver circuit and the external testing equipment. Instead of requiring complex external optical testing setups, the emulator provides a simplified electrical interface that mediates the testing process, allowing comprehensive validation of receiver performance without directly increasing the complexity of the receiver itself
Data Source
AI summary
An example photodiode emulator circuit includes: a first current source circuit; first and second transistors having sources coupled together and coupled to an output of the first current source circuit, a drain of the second transistor coupled to a first node; a third transistor coupled between a drain of the first transistor and a replica load circuit; a second current source circuit coupled to the first node; a capacitor coupled between the first node and electrical ground; and a fourth transistor having a source coupled to the first node and a drain that supplies an output current.