Oscillator Self-Trim Calibration Using Counter Difference Codes
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing oscillator calibration methods are inefficient, consuming significant test time and device die area, and require complex circuitry due to variations in semiconductor processing, necessitating a more efficient calibration process.
Innovation Solution
An apparatus comprising a reference oscillator counter circuit, a target oscillator counter circuit, a difference circuit, and a summation circuit to calculate and define a trim code based on the difference between reference and target oscillator count values, allowing for autonomous calibration of the target oscillator frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If known oscillator calibration techniques are used, then frequency calibration can be achieved, but test time is significantly consumed and device die area is occupied
Solution Approach 1:
The patent applies preliminary action by pre-calculating trim codes during wafer sort testing and storing them in non-volatile memory. This allows the oscillator to be pre-calibrated before final assembly, eliminating the need for time-consuming calibration at final test. The frequency calibration is performed in advance when the device is still on the wafer, and the results are retained for later use.
Solution Approach 2:
The calibration process is segmented into two distinct phases: wafer sort calibration and final test calibration. The wafer sort phase performs the actual frequency measurement and trim code calculation, while the final test phase only needs to retrieve and apply the pre-calculated trim codes. This segmentation allows the complex calibration work to be done when time is abundant (wafer sort) rather than when time is constrained (final test).
2Measurement precision
If known oscillator calibration techniques are used, then frequency calibration can be achieved, but device die area is occupied by calibration circuitry
Solution Approach 1:
The patent extracts the complex calibration circuitry from the final device and relocates it to the wafer sort test environment. The frequency measurement and trim code calculation functions are performed by external test equipment during wafer sort, and only the minimal necessary components (counter circuits and memory for storing trim codes) remain in the final device. This extraction significantly reduces the die area required for calibration functionality.
3Measurement precision
If iterative frequency measurement and correction is performed, then oscillator frequency can be calibrated, but calibration process becomes complex and time-consuming
Solution Approach 1:
The complex iterative frequency measurement and correction process is performed in advance during wafer sort testing. The trim codes resulting from this complex calibration are calculated and stored before the device reaches final assembly. This moves the complexity to a stage where it can be handled by external test equipment rather than requiring complex on-chip calibration circuitry.
Solution Approach 2:
Instead of implementing complex iterative calibration circuitry in the final device, the patent uses a simplified copy approach: the final device contains only counter circuits and memory that replicate the essential functionality of the full calibration system. The actual complex calibration algorithm is executed externally during wafer sort, and its results are copied into the device's non-volatile memory for later use.
Data Source
AI summary
In one general aspect, an apparatus can include a reference oscillator counter circuit configured to produce a reference oscillator count value based on a reference oscillator signal, and a target oscillator counter circuit configured to produce a target oscillator count value based on a target oscillator signal where the target oscillator signal has a frequency targeted for calibration against a frequency of the reference oscillator signal. The apparatus can include a difference circuit configured to calculate a difference between the reference oscillator counter value and the target oscillator counter value, and a summation circuit configured to define a trim code based on only a portion of bit values from the difference.