VCO Comparison Circuit for Offset-Cancelled Frequency Stability
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Solution Overview
Problem
Prior art oscillator systems suffer from frequency accuracy reduction and stability issues due to mismatches and flicker noise in amplifier devices, causing offset voltage and noise that affect the accuracy and stability of oscillation signals.
Innovation Solution
A multi-phase comparison circuit is introduced, where a sampled voltage of the amplifier output is generated during a sampling phase and compared with the output of the frequency to voltage circuit during a comparison phase to negate or minimize the offset voltage, thereby stabilizing the frequency of the voltage controlled oscillator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional amplifier-based comparison circuit is used to compare the output of the frequency to voltage circuit with a reference voltage, then the oscillator system can function, but offset voltage and flicker noise from the amplifier reduce frequency accuracy and stability
Solution Approach 1:
The comparison operation is divided into two distinct phases: a sampling phase where the amplifier output is captured, and a comparison phase where the sampled value is compared with the frequency-to-voltage circuit output. This temporal segmentation allows the offset voltage to be measured and subtracted separately, preventing it from degrading frequency accuracy while maintaining system reliability
Solution Approach 2:
The amplifier output is sampled and stored in a capacitor during the sampling phase before the comparison phase begins. This preliminary action captures the offset voltage in advance, allowing it to be compensated for during the subsequent comparison phase, thereby improving frequency accuracy without compromising system stability
Data Source
AI summary
An oscillator system includes a voltage controlled oscillator (VCO) circuit. The VCO circuit includes an output for providing an oscillation signal and input to receive a voltage that controls the frequency of the oscillation signal. The oscillator system includes a frequency to voltage circuit that receives the oscillation signal and produces a voltage that is dependent upon the frequency of the oscillation signal. The oscillator system includes a comparison circuit including an amplifier. The amplifier includes an inverting input, a non inverting input, and an output. During a first phase of the comparison circuit, the non inverting input receives a reference voltage and the inverting input is coupled to the output of the amplifier via a switch and to a capacitor wherein the capacitor samples the voltage of the output. During a second phase of the comparison circuit, the non inverting input receives the voltage produced by the frequency to voltage circuit and the switch between amplifier output and inverting input is open wherein the inverting input is coupled to the capacitor to receive the sampled voltage value. During the second phase, the output of the amplifier is provided to the input of the VCO circuit.