VCO Self-Test Circuit Using RF Peak Detection at Wafer Level
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Solution Overview
Problem
Conventional built-in self-test circuits for semiconductor wafers are inadequate in evaluating the AC characteristics of voltage controlled oscillators (VCOs), leading to potential failures in radio frequency performance that are not detected until the packaging stage, resulting in increased costs and reduced yield.
Innovation Solution
A built-in self-test circuit incorporating a radio frequency (RF) peak detector, coupled with a buffer and low pass filters, converts the amplitude of the AC signal from a cross-coupled VCO into a DC value, allowing for the identification of failed VCOs before packaging by generating a proportional DC output, which indicates the AC signal's amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional built-in self-test circuits are used to test VCOs, then open-circuit, short-circuit and DC characteristics can be detected, but AC characteristics and radio frequency performance cannot be properly evaluated
Solution Approach 1:
The patent introduces an RF peak detector as an intermediary component that bridges the gap between conventional DC testing and AC signal evaluation. The detector converts the AC output signal of the VCO into a DC voltage proportional to the signal amplitude, which can then be measured by conventional DC voltmeters. This intermediary conversion enables comprehensive VCO testing without requiring complex RF measurement equipment at the wafer level.
2Ease of manufacture
If wafer level testing is performed with insufficient testing capabilities, then testing cost is reduced, but defective VCOs are not detected and fail final packaged chip test
Solution Approach 1:
The self-test circuit is integrated directly into the VCO device at the wafer level, enabling the VCO to test itself without requiring external complex testing equipment. The RF peak detector and associated circuitry are built-in, allowing the VCO's own output signal to be converted and measured by simple DC voltmeters. This self-service approach maintains low testing costs while significantly improving defect detection capability.
3Device complexity
If AC characteristics of VCO are not tested at wafer level, then testing complexity is reduced, but radio frequency performance defects are not detected until packaging stage
Solution Approach 1:
The patent transforms the measurement parameter from direct AC signal amplitude (which requires complex RF equipment) to DC voltage (which can be measured by simple voltmeters). The RF peak detector performs this parameter transformation by converting the AC output signal of the VCO into a proportional DC voltage. This parameter change enables early detection of RF performance defects using simple DC measurement equipment, saving time without significantly increasing circuit complexity.
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 enables the early detection of defective VCOs during the wafer level testing, reducing unnecessary costs and time in subsequent semiconductor fabrication steps by ensuring only functional VCOs are packaged, thereby improving yield and reducing packaging costs.
Implementation Method 1
an RF peak detector configured such that: when the VCO generates an AC signal, the RF peak detector detects the amplitude of the AC signal and generates a DC output proportional to the amplitude of the AC signal
Data Source
AI summary
A built-in self-test circuit for testing a voltage controlled oscillator comprises a voltage controlled oscillator, a buffer having an input coupled to an output of the voltage controlled oscillator and a radio frequency peak detector coupled to the output of the buffer. The radio frequency peak detector is configured to receive an ac signal from the voltage controlled oscillator and generate a dc value proportional to the ac signal at an output of the radio frequency peak detector. Furthermore, the output of the radio frequency peak detector generates a dc value proportional to an amplitude of the ac signal from the voltage controlled oscillator when the voltage controlled oscillator functions correctly. On the other hand, the output of the radio frequency peak detector is at zero volts when the voltage controlled oscillator fails to generate an ac signal.