Built-In TIA Gain Measurement Circuit Using Internal Test Current
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Solution Overview
Problem
Current methods for testing trans-impedance amplifiers in batch production are inefficient, costly, and require expensive equipment, as they rely on external devices and complex setups, making it difficult to accurately measure gain without altering the amplifier's properties.
Innovation Solution
A circuit with a built-in current source, comprising a constant reference voltage source, reference current generator, clock source, AC switch, and off-chip precision resistor, allows for direct and precise measurement of trans-impedance amplifier gain without external equipment, using a voltage amplitude sampling device to calculate gain as Zt=Vout/Iin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external expensive equipment like network analyzers with optical interface are used for TIA testing, then measurement accuracy is improved, but testing cost increases significantly
Solution Approach 1:
The TIA chip performs self-testing by generating its own test current internally through a current source circuit, eliminating the need for external photodiodes and expensive network analyzers. The chip measures its own trans-impedance gain using built-in functional blocks, making the testing process independent of costly external equipment while maintaining measurement accuracy.
Solution Approach 2:
The invention extracts and integrates the photodiode function directly into the TIA chip's current source circuit. By removing the external photodiode requirement and replacing it with an integrated current generation circuit, the system eliminates dependence on expensive external optical equipment while achieving the same measurement objective.
2Measurement precision
If external photodiodes and complex testing setups are used, then gain measurement is achieved, but device complexity and testing time increase
Solution Approach 1:
The invention merges the test current source, the TIA amplifier, and the measurement functionality into a single integrated chip. By combining these previously separate components (external photodiode, TIA chip, network analyzer) into one unified device, the testing setup complexity is dramatically reduced while maintaining full gain measurement capability.
Solution Approach 2:
The TIA chip is designed with multi-functionality, incorporating both the amplifier function and the test current source function within the same device. This universal design allows the chip to perform both signal amplification and self-testing operations, eliminating the need for separate external testing equipment and simplifying the overall system.
3Productivity
If batch testing is conducted before packaging, then testing efficiency is improved, but the inability to use packaged photodiodes limits measurement accuracy
Solution Approach 1:
The chip performs self-testing during batch production before packaging, using an integrated current source that eliminates the need for external photodiodes. This self-service capability allows accurate trans-impedance measurement to be conducted at the optimal batch-testing stage, combining high productivity with maintained measurement accuracy.
Data Source
AI summary
A circuit for automatically measuring gain of a built-in trans-impedance amplifier includes a current source built in a trans-impedance amplifier chip for generating a constant current to an input end of the trans-impedance amplifier. The circuit samples a voltage amplitude at an output end of the trans-impedance amplifier using a voltage amplitude sampling device, and calculates the gain of the trans-impedance amplifier. The current source has a constant reference voltage source, a reference current generator, a clock source, an AC switch, and an off-chip precision resistor. The circuit is configured to measure gain of trans-impedance amplifiers directly.