Continuous-Time Delta-Sigma ADC With Linear Gm-VCO Quantization
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Solution Overview
Problem
Existing continuous-time delta-sigma analog-to-digital converters face challenges with noise-power efficiency, linearity, and bandwidth due to the linearity issues of integrators and VCO-based quantizers, leading to reduced input voltage swing and degraded system linearity.
Innovation Solution
The proposed solution involves a continuous-time delta-sigma analog-to-digital converter with a linear integrator using a linear Gm circuit and a body-driven VCO, along with an FIR filter on the delta-sigma feedback loop to prevent aliasing and boost input impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a VCO-based quantizer is used in an existing continuous-time delta-sigma ADC, then low-power operation is achieved, but the input voltage swing is reduced and system linearity is degraded
Solution Approach 1:
The patent changes the control parameter of the VCO from voltage to current. The linear Gm circuit generates a linearly changing current that controls the VCO, avoiding the linearity issues of voltage-controlled VCOs while maintaining low-power operation. This parameter transformation resolves the contradiction between low power consumption and maintained linearity.
Solution Approach 2:
The patent introduces a linear Gm circuit as an intermediary between the integrator and the VCO-based quantizer. This intermediate stage converts the voltage output of the integrator into a current that linearly controls the VCO, preventing direct voltage swing issues from affecting the VCO's linearity while maintaining the low-power advantage of VCO-based quantization.
2Adaptability or versatility
If a large input voltage swing is applied to the integrator, then the signal range is increased, but the linearity is reduced due to quantization noise
Solution Approach 1:
The patent replaces the voltage-based control mechanism with a current-based control mechanism for the VCO. By using a linear Gm circuit to generate a linearly changing current instead of directly applying voltage swing to the VCO, the system achieves larger effective input range while maintaining linearity through the current control path.
3Extent of automation
If the non-linear KVCO of a VCO-based quantizer is used, then the quantization function is achieved, but the system linearity is greatly degraded
Solution Approach 1:
The patent changes the control parameter from voltage to current, and specifically uses current that linearly changes with the input signal. This transformation allows the inherently non-linear VCO to produce linear output frequency modulation when controlled by the linear Gm circuit's current, resolving the linearity degradation issue while maintaining quantization functionality.
Data Source
AI summary
Disclosed are a continuous-time delta-sigma analog-to-digital converter and an operation method thereof. More particularly, a continuous-time delta-sigma analog-to-digital converter, including: a linear integrator configured to generate a first output signal corresponding to a preset input voltage based on an operation of a linear Gm circuit that receives the preset input voltage; and a quantizer configured to generate a second output signal corresponding to the first output signal based on an operation of a body-driven VCO that receives the first output signal and to generate a digital output code corresponding to the second output signal based on an operation of a Frequency to Digital Converter (FDC) that receives the second output signal is disclosed.