Single-Pin Interface Circuit for Electronic Device Testing
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Solution Overview
Problem
Electronic devices with limited pins, particularly in automotive and sensor applications, face challenges in testing due to the requirement of four pins for scan shift interface, which is not feasible, and existing solutions for single-pin communication do not effectively apply test patterns or capture responses.
Innovation Solution
A method using a data stream with three level bands is input through a single logic pin, decoding signals like scan_in, scan_shift_enable, and scan_clock, and generating a scan_out signal, enabling the transmission of these signals over a single wire through a duplex interface circuit with a level detection circuit and decoder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If four pins are used for scan shift interface, then testing capability is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple control signals (scan clock, scan in, scan shift enable, scan out) into a single data stream transmitted over one pin. The interface circuit multiplexes these functions by encoding them as different voltage levels (three-level signal) within the data stream, allowing one pin to perform the work of four pins.
Solution Approach 2:
The patent transitions from spatial multiplexing (separate pins for separate signals) to temporal/encoding multiplexing (multiple signals encoded in time and voltage levels within a single stream). By using three voltage levels instead of binary states, the system encodes multiple control signals within a single data stream, effectively adding a dimension of signal encoding.
2Device complexity
If single pin interface is used, then device complexity is reduced, but testing capability deteriorates
Solution Approach 1:
The patent segments the data stream into distinct temporal slots, each carrying a specific control signal (scan clock, scan in, scan shift enable, or scan out). The interface circuit identifies which signal is being transmitted at each time step, allowing the single pin to independently control all scan shift register operations that would traditionally require multiple pins.
Solution Approach 2:
The patent changes the parameter of signal encoding from binary (two voltage levels) to ternary (three voltage levels). This allows the single data stream to encode multiple control signals simultaneously by varying the voltage level, thereby maintaining full testing capability while using only one pin.
3Device complexity
If fixed baud rate interface is used, then communication is simplified, but adaptability deteriorates
Solution Approach 1:
The patent implements a dynamic interface where the data stream can adapt its structure based on the test pattern length. The interface circuit detects the scan_shift_enable signal to identify the start of test pattern transmission and automatically adjusts the timing and decoding accordingly. This allows the same single-pin interface to handle variable-length test patterns without requiring fixed baud rate configurations or complex reconfiguration.
Data Source
AI summary
A method and interface circuit for testing an electronic device with a single logic pin is disclosed. The comprises forming a data stream having three level bands; inputting the data stream through a single logic pin; and decoding the data stream to identify a scan_in signal, a scan_shift_enable signal and a scan_out signal and returning contemporaneously a scan_out signal as an output through the same logic pin. The interface circuit includes a decoder connected to the single logic pin.