Differential VCO ADC Phase Detection for Low-Distortion Conversion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing analog to digital converters using VCOs face challenges with harmonic distortion due to non-linear V-to-frequency transfer functions and are affected by process and temperature variations, leading to DC offsets and reduced dynamic range.
Innovation Solution
An analog to digital converter with a differential VCO that uses a phase domain, incorporating multiple VCOs and samplers to detect phase differences without a reference frequency, and a data weighted averaging algorithm to minimize errors, thereby increasing output range and dynamic range while reducing power consumption and area requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a frequency based VCO delta sigma modulator is used, then the converter can operate with a simple structure, but harmonic distortion occurs in the output signal due to non-linear V-to-frequency transfer function
Solution Approach 1:
The patent changes the operating domain from frequency to phase by using a phase detector instead of a frequency counter. The VCO transfer function is changed from V-to-frequency to V-to-phase, which has integration relation and reduces non-linear effects. This parameter change in the measurement domain resolves the harmonic distortion issue while maintaining structural simplicity.
Solution Approach 2:
The patent substitutes the frequency counting mechanism with a phase detection mechanism. Instead of measuring frequency directly (which requires complex timing and counting circuits), the system uses phase comparison between VCO output and reference signal, replacing mechanical frequency measurement with a more accurate phase-based measurement system.
2Object-generated harmful factors
If a phase frequency based VCO delta sigma modulator is used, then harmonic distortion is reduced, but DC offset occurs when reference frequency and VCO common frequency are different
Solution Approach 1:
The patent introduces asymmetry in the frequency relationship between the VCO and reference oscillator by deliberately designing the VCO to operate at twice the reference frequency (2x relationship). This asymmetric frequency ratio prevents the DC offset problem that occurs with equal frequencies, as the phase difference continuously varies, averaging out offset errors over time.
Solution Approach 2:
The patent utilizes periodic action by operating the VCO at a harmonic frequency (2x) of the reference signal. This periodic relationship with a specific frequency ratio creates a predictable phase evolution pattern that allows the phase detector to accurately measure phase differences while the periodic nature averages out DC offsets over complete cycles.
3Adaptability or versatility
If digital logic VCO is used, then the VCO can be integrated with digital circuits, but frequency appears different under same DC voltage due to process or temperature conditions
Solution Approach 1:
The patent implements feedback by using the phase detection output to control the VCO through the delta-sigma modulator loop. The error signal from phase comparison is filtered and fed back to adjust the VCO control voltage, creating a closed-loop system that automatically compensates for process and temperature variations, thereby stabilizing the output frequency despite environmental changes.
Solution Approach 2:
The patent makes the VCO universally adaptable to different operating conditions by designing it as a digitally controlled oscillator that can be precisely tuned through the feedback loop. The VCO serves multiple functions: it generates the oscillating signal, responds to digital control words, and its frequency is automatically adjusted by the phase-locked feedback mechanism to maintain accuracy across process and temperature variations.
4Reliability
If additional circuits are added to compensate for frequency variations, then frequency stability improves, but area and power consumption increase
Solution Approach 1:
The patent merges the frequency stabilization function into the existing phase detector and feedback loop of the delta-sigma modulator. Instead of adding separate frequency control circuits, the phase detection and feedback mechanism is designed to simultaneously perform both phase measurement and frequency regulation, consolidating multiple functions into a unified circuit structure that minimizes area and power consumption.
Data Source
AI summary
An analog to digital converter is provided. The analog to digital converter includes: an arithmetic operator combining an analog input signal with a feedback signal; a loop filter filtering an output signal of the arithmetic operator; a quantizer quantizing an output signal of the loop filter to output a digital signal; and a feedback converting the digital signal to output a feedback signal, in which the quantizer includes: a plurality of VCOs each receiving a positive output signal and a negative output signal of the loop filter and outputting VCO signals; a plurality of samplers receiving the VCO signals output from the plurality of VCOs, respectively and outputting sampled signals; and a phase detector detecting a phase difference in the sampled signals output from the plurality of samplers, respectively, to detect a phase difference in two VCO signals output from the plurality of VCOs, respectively.