Crystal Oscillator Amplifier Self-Test Using Current Mirror Bias Codes
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Solution Overview
Problem
Conventional methods for testing the transconductance of crystal oscillator amplifiers are costly, time-consuming, and increase the time to market for final products.
Innovation Solution
A built-in self-test (BIST) configuration that includes a current mirror circuit, test switch, analog-to-digital converter (ADC), digital-to-analog converter (DAC), and test control circuitry to estimate the transconductance of the crystal oscillator amplifier without external hardware instruments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional hardware-based measurement methods are used to test transconductance, then measurement accuracy can be achieved, but testing becomes costly and time-consuming
Solution Approach 1:
The crystal oscillator amplifier tests its own transconductance parameter using built-in test circuitry (current mirror, ADC, DAC) integrated within the device itself, eliminating the need for external measurement equipment and enabling self-diagnosis during manufacturing
Solution Approach 2:
The amplifier circuit is designed to perform both its primary oscillation function and transconductance measurement function using shared circuit elements, allowing the same hardware to serve multiple purposes without requiring separate dedicated test equipment
2Measurement precision
If conventional hardware-based measurement methods are used to test transconductance, then accurate testing can be performed, but device complexity and cost increase
Solution Approach 1:
The test measurement functions are merged with the amplifier circuit by integrating current mirror circuitry, ADC, and DAC directly into the amplifier device, combining testing capabilities with the main functional circuit rather than using separate external instruments
Solution Approach 2:
The current mirror circuit creates a copy of the amplifier's output current to generate a test voltage signal, allowing indirect measurement of transconductance through a replicated signal path that can be easily converted to digital form
3Measurement precision
If conventional measurement methods are used, then transconductance can be measured, but production efficiency decreases
Solution Approach 1:
The manual hardware-based measurement process is replaced with an automated digital measurement system that uses ADC to convert test signals and DAC to generate test inputs, eliminating the need for manual operation of external instruments and enabling automated production testing
Solution Approach 2:
The device performs self-testing through integrated circuitry that automatically measures its own transconductance parameter without requiring external test equipment or manual intervention, streamlining the production testing process
Data Source
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AI summary
The present disclosure relates to a BIST system and method for a crystal oscillator amplifier including current mirror circuitry, an ADC, a DAC, and test control circuitry. The amplifier includes a current source, a base transistor and a feedback resistor. The ADC converts a self-bias voltage on an input node into a digital bias code during a normal mode when the current source is coupled to the base transistor. During phases of a test mode, the base transistor is coupled instead to the mirror circuitry, which mirrors current through the base transistor into a test resistor. The digital bias code is converted into upper and lower digital bias codes using a delta value, which are converted by the DAC into corresponding bias voltages driven onto the input node during respective phases of the test mode. The ADC converts corresponding test voltages on the test resistor into test codes used to estimate the amplifier transconductance.