Resonator Oscillator Offset Cancellation for Low Allan Deviation
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Solution Overview
Problem
Resonator-based oscillators suffer from high 1/f noise corner frequencies, leading to significant near-phase noise, which conventional technologies have not effectively mitigated.
Innovation Solution
The implementation of active offset cancellation in sustaining amplifiers, specifically through auto-zeroing techniques and parallel inverting amplifiers, reduces the 1/f noise corner frequency from approximately 5 KHz to less than 10 Hz or 1 Hz, thereby lowering near-phase noise by 20 to 30 dB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sustaining amplifiers are used in resonator-based oscillators, then the oscillator can maintain continuous operation, but the 1/f noise corner frequency remains high (approximately 5 KHz), resulting in significant near-phase noise
Solution Approach 1:
The sustaining amplifier is divided into two separate amplifiers: a first sustaining amplifier that operates continuously to maintain oscillator operation, and a second sustaining amplifier that operates periodically to reduce offset voltage. This segmentation allows each amplifier to have specialized functions, with the first ensuring continuous operation and the second targeting noise reduction without compromising reliability
Solution Approach 2:
The second sustaining amplifier operates periodically rather than continuously, with its output coupled to the first sustaining amplifier through a switch that closes periodically. This periodic action allows the second amplifier to reduce offset voltage at specific intervals, lowering the 1/f noise corner frequency while the first amplifier maintains continuous operation for reliability
2Object-affected harmful factors
If offset voltage reduction techniques are applied to sustaining amplifiers, then the 1/f noise corner frequency decreases to less than 10 Hz, but the device complexity increases due to additional circuitry
Solution Approach 1:
The offset reduction function is merged into the existing sustaining amplifier structure by adding a second amplifier that periodically operates in conjunction with the first. Rather than creating a completely separate offset cancellation system, the invention integrates noise reduction capability into the existing amplifier framework through controlled periodic operation and switching, reducing overall system complexity
Solution Approach 2:
The second sustaining amplifier performs preliminary offset voltage reduction before the offset can significantly impact noise performance. By periodically reducing the offset voltage in advance, the system prevents the accumulation of large offset values that would otherwise contribute to high 1/f noise, thereby achieving low noise corner frequency without requiring continuous complex correction circuitry
Data Source
AI summary
An oscillator includes a resonator, sustaining circuit and detector circuit. The sustaining circuit receives a sense signal indicative of mechanically resonant motion of the resonator generates an amplified output signal in response. The detector circuit asserts, at a predetermined phase of the amplified output signal, one or more control signals that enable an offset-reducing operation with respect to the sustaining amplifier circuit.