Oscillator Trim Control for Temperature-Stable Clock Frequency
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Solution Overview
Problem
Oscillator circuits in integrated circuits often produce clock frequencies that vary significantly with temperature, which can lead to inaccuracies in automotive applications where devices need to function across a wide temperature range without significant frequency deviations.
Innovation Solution
An integrated circuit design that includes a temperature sensing circuit, non-volatile storage, and a digital control circuit to dynamically adjust the trim code for the oscillator circuit, using a combination of constant and proportional to absolute temperature current sources to reduce temperature dependence on the oscillator's output frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional oscillator circuits are used without temperature compensation, then the device complexity is low, but the frequency stability across temperature varies significantly
Solution Approach 1:
The oscillator circuit dynamically adjusts its operating parameters by applying different trim codes based on detected temperature conditions. The circuit transitions from a static configuration to a dynamic one where the trim code changes with temperature, thereby maintaining frequency stability across varying thermal environments without requiring a completely redesign of the oscillator architecture.
Solution Approach 2:
The invention changes the electrical parameters of the oscillator circuit by applying different trim codes that adjust capacitor ratios or other critical parameters. This parameter adjustment compensates for temperature-induced frequency drift, allowing the oscillator to maintain accurate frequency output across the temperature range of -40°C to 150°C while adding minimal circuit complexity.
2Measurement precision
If temperature sensing and dynamic trim code adjustment circuits are added, then the frequency accuracy across temperature is improved to within ±3%, but the device complexity increases
Solution Approach 1:
The system performs preliminary temperature assessment and applies appropriate trim codes in advance before frequency drift becomes problematic. The temperature sensing circuit continuously monitors conditions and pre-adjusts the trim code to compensate for upcoming frequency deviations, ensuring accuracy is maintained proactively rather than reactively.
Solution Approach 2:
The invention implements a feedback mechanism where the temperature sensing circuit continuously monitors the thermal state and feeds this information to the control logic, which then adjusts the trim code accordingly. This closed-loop feedback system automatically corrects frequency deviations caused by temperature changes, achieving ±3% accuracy while keeping the additional circuit complexity manageable through efficient feedback control.
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
The solution results in a clock frequency that is much less variable with temperature, meeting the requirements for automotive applications by maintaining accuracy within ±3% across the temperature range of −40°C to 150°C.
Implementation Method 1
The first current source is configured to generate a current to the capacitor that is proportional to absolute temperature
Data Source
AI summary
An oscillator circuit includes a comparator having first and second inputs, the first input configured to be coupled to a reference voltage. The oscillator circuit also includes a capacitor and a first current source. The capacitor is coupled between the second input and ground. The first current source is coupled between a supply voltage terminal and the capacitor. The first current source is configured to generate a current to the capacitor that is proportional to absolute temperature.