Chopper Stabilized Reference Circuit for Oscillator Frequency Stability
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Solution Overview
Problem
Existing reference circuits for generating reference voltage and current are unstable with respect to temperature, affecting the performance and operating range of oscillators that rely on these signals, leading to limited accuracy and frequency stability.
Innovation Solution
A reference circuit comprising a voltage reference generator using chopper stabilization and curvature compensation techniques, and a current reference generator with level shifter and canceller circuits to generate a second-order temperature-compensated current, reducing the dependency on reference voltage variations and improving frequency stability across temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reference voltage is used for oscillator operation, then the oscillator can generate oscillation signals, but the frequency stability with respect to temperature becomes dependent on the reference voltage stability
Solution Approach 1:
The patent changes the operating parameters by using a current reference instead of a voltage reference, and specifically uses a second-order temperature-compensated current reference that maintains constant current across temperature variations. This parameter change eliminates the frequency stability dependency on reference voltage stability.
Solution Approach 2:
The patent substitutes the voltage reference mechanism with a current reference mechanism. By replacing the voltage-based system with a current-based system that has inherent temperature compensation, the patent eliminates the harmful dependency of frequency stability on reference voltage stability.
2Measurement precision
If the oscillating frequency is highly dependent on the reference voltage, then accuracy can be maintained, but the operating temperature range becomes limited
Solution Approach 1:
The patent changes the reference parameter from voltage to current, and specifically implements a second-order temperature-compensated current reference. This parameter change allows the oscillator to maintain high accuracy across a wide operating temperature range by compensating for temperature effects on the reference current.
3Measurement precision
If extensive temperature trimming is performed to improve frequency stability, then accuracy is improved, but production complexity and cost increase
Solution Approach 1:
The patent implements a self-compensating reference current circuit that automatically maintains constant current across temperature variations without requiring external trimming or calibration. The second-order temperature compensation is built into the circuit architecture, allowing it to self-correct for temperature effects and eliminating the need for extensive temperature trimming during production.
Data Source
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AI summary
A reference circuit, an oscillator architecture that includes the reference circuit and a method for operating the reference circuit are described. In one embodiment, the reference circuit includes a voltage reference generator configured to generate a reference voltage and a current reference generator configured to generate a reference current based on the reference voltage. The current reference generator includes a level shifter circuit configured to generate intermediate voltages based on the reference voltage, a first current reference circuit configured to generate intermediate currents based on the intermediate voltages, where the intermediate currents are correlated to the reference voltage, and a second current reference circuit configured to combine the intermediate currents to generate the reference current. Other embodiments are also described.