LVDS Receiver Loopback Circuit for Common-Mode Range Testing
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Solution Overview
Problem
LVDS receiver testing often fails to cover the entire common mode voltage range during manufacturing, allowing defects to go undetected due to limited testing capabilities, especially for receivers with wide common mode voltage ranges.
Innovation Solution
A loopback circuit with a dummy transmitter that generates test differential signals based on a tunable common mode voltage, allowing for comprehensive testing of the receiver's common mode range, including during operation, and enabling concurrent testing of multiple receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LVDS receiver is designed for wide common mode voltage range, then adaptability is improved, but testing completeness deteriorates because single voltage testing cannot cover entire range
Solution Approach 1:
The patent implements a tunable common mode voltage source that can dynamically adjust the common mode voltage level during testing. This allows the test system to sweep through multiple voltage points across the entire common mode range, transforming a static single-voltage test into a dynamic multi-voltage test that comprehensively covers the receiver's operating range.
Solution Approach 2:
The patent changes the voltage parameter of the common mode signal during testing by introducing a tunable voltage source. This enables the test to explore different operating conditions (different common mode voltage levels) and verify receiver performance across the full specified range, rather than at a fixed voltage point.
2Reliability
If dummy transmitter is added for loopback testing, then testing capability is improved, but device complexity increases
Solution Approach 1:
The dummy transmitter circuit is designed to serve multiple functions: it acts as a signal source for loopback testing, provides tunable common mode voltage generation, and enables both functional and electrical characteristic testing. This multi-functionality justifies the added complexity by consolidating multiple test capabilities into a single integrated test structure.
Solution Approach 2:
The loopback test structure enables the receiver to test itself by feeding its own output back to its input through the dummy transmitter. This self-service capability allows the device to perform autonomous functional verification without requiring external test equipment for basic operational testing.
3Measurement precision
If tunable common mode voltage is implemented, then measurement precision is improved, but device complexity increases due to additional components
Solution Approach 1:
The patent introduces a tunable common mode voltage source that can dynamically adjust the voltage level to match different operating conditions. This dynamic adjustment capability enables precise measurement of receiver performance at various common mode voltage points, transforming static testing into adaptive testing that follows the actual operating range.
Solution Approach 2:
The tunable common mode voltage source is configured beforehand to provide predetermined voltage levels corresponding to the minimum and maximum common mode voltage specifications. This preliminary configuration allows the test to systematically cover the entire operating range without requiring complex real-time adjustments during execution.
Data Source
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AI summary
A low voltage differential signaling (LVDS) receiver includes a receiver circuit including first and second inputs coupled to first and second conductive pads, respectively, and an output coupled to an input of a digital controller, and a dummy transmitter circuit including a first input coupled to receive a common mode voltage (VCM) tune signal, a second input coupled to a loopback input signal, a third input coupled to a loopback enable signal, a first output coupled to the first input of the receiver circuit, and a second output coupled to the second input of the receiver circuit. When a test mode of operation is enabled, the digital controller asserts the loopback enable signal, and the dummy transmitter circuit generates a pair of test differential signals based on the VCM tune signal, wherein the VCM tune signal varies to test the LVDS receiver over a range of common mode voltages.