On-Chip Oscillator Trimming Using Internal Frequency Measurement
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Solution Overview
Problem
Conventional oscillator trimming processes on integrated circuits are time-consuming due to the need for external test equipment to measure oscillation frequencies, especially when dealing with noisy signals, large sets of trim values, or non-monotonic transfer characteristics.
Innovation Solution
An oscillator trim program is stored in the integrated circuit's read-only memory, which uses a timer and interrupt mechanism to measure frequencies internally, allowing for autonomous trimming with selectable search algorithms and enabling the use of a less costly tester.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external test equipment is used to measure oscillation frequencies during trimming, then measurement capability is provided, but trimming time becomes excessively long
Solution Approach 1:
The oscillator trimming system performs frequency measurements autonomously using an on-chip timer and counter circuit that counts oscillator periods directly. The microcontroller reads the counter value to determine frequency, eliminating the need for external test equipment to perform measurements. This self-service approach reduces trimming time by allowing parallel operation of multiple oscillators simultaneously while maintaining accurate frequency measurement capability.
2Manufacturing precision
If the set of trim values to be tested is large, then trimming accuracy can be improved, but test time increases significantly
Solution Approach 1:
The system implements a continuous trimming process where the microcontroller automatically iterates through trim values and performs frequency measurements without external intervention. The on-chip timer and counter enable continuous monitoring of oscillator frequency, allowing the system to efficiently evaluate multiple trim values in sequence or parallel, maintaining high trimming accuracy while minimizing idle time between measurements.
3Productivity
If multiple oscillators are trimmed simultaneously, then productivity increases, but measurement complexity increases
Solution Approach 1:
The measurement system is segmented into independent on-chip timer and counter units that can operate autonomously for each oscillator. The microcontroller divides the trimming task by assigning specific timer/counter resources to individual oscillators, allowing simultaneous measurement and trimming of multiple oscillators without requiring a complex external measurement system. This segmentation enables parallel processing while keeping each measurement channel simple and independent.
4Measurement precision
If frequency measurements are averaged over multiple periods, then measurement accuracy improves for noisy signals, but measurement time increases
Solution Approach 1:
The on-chip counter circuit performs preliminary accumulation of oscillator period counts over multiple cycles before the microcontroller reads the final value. This preliminary action of continuous counting during the measurement interval allows the system to average multiple periods inherently through the counter accumulation process, improving accuracy for noisy signals without requiring sequential repeated measurements that would increase total measurement time.
Data Source
AI summary
Oscillation frequency measurements for trimming oscillators on an integrated circuit device are performed entirely on the device. The oscillation frequency measurements utilize a reference clock. Some measurements count periods of the oscillator signal independently of the reference clock, and some measurements count periods of the reference clock independently of the oscillator signal. After one oscillator on the device has been trimmed, that trimmed oscillator may then be used to make oscillation frequency measurements for trimming another oscillator on the device.