VCO Comparison Circuit for Offset-Canceled Frequency Control
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Solution Overview
Problem
Prior oscillator systems face issues with frequency accuracy and stability due to mismatches and flicker noise in amplifiers, leading to offset voltages that affect the accuracy and stability of the oscillator output.
Innovation Solution
A multi-phase comparison circuit is introduced, where the output of the amplifier is sampled during one phase and compared with the frequency-to-voltage circuit output during another phase, effectively canceling out offset voltages and minimizing noise impact on the voltage-controlled oscillator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a continuous comparison method is used to control the VCO frequency, then the frequency control responsiveness is improved, but the offset voltage and flicker noise from the amplifier reduce the frequency accuracy and stability
Solution Approach 1:
The patent implements periodic sampling of the amplifier output at specific phases (e.g., rising and falling edges of the oscillation signal) rather than continuous monitoring. This periodic action allows the system to maintain frequency control responsiveness while eliminating the continuous exposure to offset voltage and flicker noise, thereby improving frequency accuracy and stability.
2Stability of the object's composition
If the amplifier output is continuously monitored, then the frequency control stability is improved, but the flicker noise in the amplifier reduces the overall system stability
Solution Approach 1:
The patent extracts only the necessary frequency control information from the amplifier output at specific sampling phases, rather than continuously monitoring the entire amplifier output. By taking out only the relevant data points (at rising and falling edges), the system maintains frequency control stability while eliminating the harmful flicker noise that would be present in continuous monitoring.
3Measurement precision
If the reference voltage is continuously compared with the VCO output frequency, then the frequency locking accuracy is improved, but the offset voltage in the comparator reduces the measurement precision
Solution Approach 1:
The patent performs preliminary sampling of the amplifier output at specific phases before the final frequency comparison is made. By pre-sampling the signal at controlled phases (rising and falling edges), the system establishes a stable reference point for frequency comparison that is independent of comparator offset voltage, thereby maintaining frequency locking accuracy while eliminating the harmful effect of offset voltage.
Data Source
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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.