Variable-Gain Comparator for Faster SAR ADC Conversion
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Solution Overview
Problem
Existing analog-to-digital converters, particularly those of the successive approximation type, face challenges in meeting high performance requirements due to limitations in comparator design, such as restricted bandwidth and gain, which affect the efficiency of signal conversion and processing time.
Innovation Solution
The implementation of a variable-gain fully-differential amplifier with a single switch for adjusting output impedance, allowing dynamic gain adaptation, is introduced. This amplifier is integrated into the comparator of an analog-to-digital converter, enabling complementary variation of bandwidth and gain, optimizing the time budget for conversion cycles and reducing parasitic capacitance for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional fixed-gain amplifier is used in the comparator, then the circuit structure is simple, but the bandwidth and gain cannot be adapted dynamically, limiting conversion speed and precision
Solution Approach 1:
The patent implements a variable-gain amplifier where the gain can be dynamically adjusted during the conversion process. The amplifier transitions from a high-gain state during the acquisition phase to a low-gain state during the conversion phase, enabling adaptive performance optimization without requiring multiple fixed-gain stages.
Solution Approach 2:
The amplifier's gain parameter is changed dynamically by controlling the switching state of the capacitor. When the switch is in the first state, the amplifier operates with high gain; when switched to the second state, it operates with low gain. This parameter change enables the system to adapt to different operational requirements.
2Measurement precision
If high gain is maintained throughout the conversion process, then measurement precision is improved, but the settling time increases, reducing conversion speed
Solution Approach 1:
The amplifier operates in periodic cycles with distinct phases: an acquisition phase with high gain for precise signal capture, followed by a conversion phase with low gain for rapid settling. This periodic switching between gain states allows the system to achieve both high precision and fast conversion speed by optimizing gain for each phase's specific requirements.
Solution Approach 2:
The gain is dynamically adjusted based on the conversion phase. During acquisition, high gain ensures precise signal capture; during conversion, low gain reduces settling time. This dynamic adaptation resolves the contradiction between precision and speed by optimizing gain for each operational phase.
3Measurement precision
If multiple switches are used to adjust output impedance, then bandwidth and gain control precision is improved, but parasitic capacitance increases, degrading signal quality
Solution Approach 1:
The patent extracts the impedance control function from multiple switches and implements it through a single switch controlling a capacitor's connection state. This single switch configuration minimizes parasitic capacitance while still enabling precise output impedance adjustment between high-impedance (capacitor disconnected) and low-impedance (capacitor connected) states.
Solution Approach 2:
The output impedance parameter is changed by switching the capacitor's connection state. When the switch connects the capacitor, the output impedance decreases; when the switch disconnects the capacitor, the output impedance increases. This single-parameter control method achieves precise impedance adjustment without introducing multiple switches and their associated parasitic capacitances.
Data Source
AI summary
A converter may include an input terminal to receive a first analog signal, a digital-to-analog converter to provide second analog signals related to digital values applied to the digital-to-analog converter, a comparator to receive the first and second analog signals, the comparator comprising a variable gain amplifier to provide an output signal based on a difference between the first and second analog signals, a state machine to receive the output signal of the comparator and generating the digital values applied to the digital-to-analog converter based on the output signal of the comparator, and a controller to selectively set the gain of the variable gain amplifier.