Relaxation Oscillator Current Modulation for Low-Jitter Clocks
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Solution Overview
Problem
Relaxation oscillators in integrated circuits suffer from low frequency jitter due to flicker noise from current sources and comparators, which deteriorates audio performance and is difficult to mitigate without increasing die size or power consumption.
Innovation Solution
The proposed oscillator circuit employs dynamic element matching and chopped comparators to modulate charging currents and reference currents, shifting flicker noise to higher frequencies, thereby reducing low frequency jitter without increasing die size or power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current sources and comparators are used in relaxation oscillators, then the oscillator can be implemented with standard circuit components, but flicker noise from these components causes low frequency jitter that deteriorates audio performance
Solution Approach 1:
The patent introduces an intermediary modulator circuit that sits between the current sources/comparators and the oscillator core. This modulator converts the flicker noise from standard components into high-frequency noise through frequency multiplication, while the oscillator core itself operates at a lower frequency. The harmful low-frequency jitter is thus transformed into less harmful high-frequency noise.
Solution Approach 2:
The patent changes the frequency parameter of the noise through modulation. By using a modulator that operates at a frequency offset from the oscillator frequency, the low-frequency flicker noise is shifted to higher frequencies. This parameter transformation converts the harmful low-frequency jitter into acceptable high-frequency noise.
2Object-affected harmful factors
If the die size or power consumption is increased to mitigate flicker noise, then noise performance may improve, but this increases device complexity and resource usage
Solution Approach 1:
Instead of increasing the size of current sources or comparators to reduce flicker noise, the patent uses a modulator as an intermediary to transform the noise characteristics. This approach maintains compact component sizes while achieving noise mitigation through frequency transformation rather than component scaling.
Solution Approach 2:
The patent changes the frequency parameter of the noise output rather than increasing component sizes. By modulating the oscillator output at a frequency offset, the flicker noise is shifted to higher frequencies where it becomes less harmful, avoiding the need for larger die area.
3Object-affected harmful factors
If the die size or power consumption is increased to mitigate flicker noise, then noise performance may improve, but this increases device complexity and resource usage
Solution Approach 1:
The modulator acts as an intermediary that transforms noise characteristics without requiring increased power consumption from the core oscillator components. The frequency transformation is achieved through switching operations that consume minimal power compared to increasing current source sizes or adding noise cancellation circuits.
Solution Approach 2:
The patent changes the noise frequency parameter through modulation rather than increasing power consumption to reduce flicker noise. This parameter transformation approach achieves noise mitigation with minimal additional power cost.
4Measurement precision
If offset cancellation of comparators is implemented, then comparator offset is reduced, but flicker noise of comparators can only be removed by chance and may still result in high frequency jitter
Solution Approach 1:
The modulator serves as an intermediary that transforms the comparator flicker noise into high-frequency noise. Even if offset cancellation is implemented, the modulator ensures that any remaining flicker noise is frequency-shifted to the high-frequency band where it becomes less harmful, providing deterministic rather than chance-based noise reduction.
Solution Approach 2:
The patent changes the frequency parameter of comparator flicker noise through modulation. By operating the modulator at a frequency offset from the oscillator frequency, the comparator noise is shifted to higher frequencies, converting a problematic low-frequency issue into an acceptable high-frequency characteristic.
Data Source
AI summary
An oscillator circuit includes a current controller, a first capacitor and a second capacitor. A current generator is coupled to the current controller, the first and the second capacitor, and is operable, under control of a control signal of the current controller, provide charging currents. A comparator stage comprises a first input coupled to the first capacitor, a second input coupled to the second capacitor and a reference input to be supplied with the reference voltage. The comparator stage further includes an oscillator output to provide a clock signal based on a comparison of the capacitor voltages and the reference voltage, respectively. A modulation circuit comprises an oscillator input to input the clock signal, a reference output is connected to the current generator, and is operable to alternate between the charging currents, such that a charging current is provided as reference current at the reference output and at least one charging current is provided to alternately charge/discharge the first capacitor and the second capacitor to respective capacitor voltages.