Transformer-Bootstrapped Track-and-Hold Switch for High-Frequency ADCs
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Solution Overview
Problem
Existing track and hold circuits face challenges in scaling to higher sampling frequencies due to parasitic capacitance limitations and inefficiencies in advanced bootstrap circuits, which lead to distortion and inefficiencies in analog-to-digital conversion, especially with large input and output voltage swings.
Innovation Solution
Incorporating a transformer-based bootstrap circuit that controls the gate-source voltage of the sampling transistor, independent of input signal amplitude, allowing for scalable and efficient high-frequency operation with reduced distortion and increased spurious-free dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bootstrap circuits using switches and capacitors are used to improve switch linearity, then switch on-state resistance independence from input signal amplitude is achieved, but the circuit becomes difficult to scale to higher sampling frequencies due to parasitic capacitances
Solution Approach 1:
The patent replaces the mechanical/electrical switch and capacitor-based bootstrap circuit with a transformer-based bootstrap circuit. The transformer uses electromagnetic coupling to achieve the same voltage boosting function without the parasitic capacitance limitations of traditional switch-capacitor implementations, enabling higher sampling frequencies while maintaining switch linearity.
Solution Approach 2:
The invention changes the fundamental operating parameters of the bootstrap circuit by using transformer turns ratio to determine voltage multiplication instead of using capacitor charge-discharge cycles. This parameter change eliminates the parasitic capacitance bottleneck and allows the circuit to operate at higher frequencies.
2Productivity
If advanced bootstrap circuits use large numbers of transistors to achieve high-frequency operation, then sampling frequency is improved, but power efficiency decreases and routing complexity increases
Solution Approach 1:
The patent extracts the essential function of voltage boosting from the complex transistor-based bootstrap circuit and implements it using a simpler transformer-based approach. This extraction eliminates the need for multiple transistors and their associated power consumption while maintaining the frequency response characteristics.
Solution Approach 2:
The transformer-based bootstrap circuit serves multiple functions simultaneously: it provides voltage boosting, isolation, and frequency transformation without requiring separate circuits for each function. This multi-functionality reduces the overall transistor count and improves power efficiency compared to advanced transistor-based implementations.
3Device complexity
If the sampling transistor on-state resistance depends on input signal amplitude, then circuit simplicity is maintained, but distortion increases due to input-dependent resistance variation
Solution Approach 1:
The transformer acts as an intermediary element that decouples the input signal amplitude from the gate-source voltage of the sampling transistor. By using electromagnetic induction, the transformer provides a fixed voltage transformation ratio that is independent of the input signal level, thereby stabilizing the transistor's on-state resistance and reducing distortion while maintaining relatively simple circuit topology.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The transformer-based bootstrap circuit enhances the scalability and power efficiency of track and hold circuits, enabling high-accuracy analog-to-digital conversion across wide input voltage ranges with reduced distortion and improved spurious-free dynamic range, particularly at high frequencies.
Implementation Method 1
The transformer has a primary winding coupled to a clock input terminal, and a secondary winding coupled between the source and gate of the transistor
Data Source
AI summary
A track and hold circuit includes a signal input terminal, a clock input terminal, an output terminal, a transistor, and a bootstrapping circuit with a transformer. The transistor includes a source, a drain, and a gate, where the source is coupled to the signal input terminal, and the drain is coupled to the output terminal. The transformer includes a primary winding coupled to the clock input terminal, and a secondary winding. The secondary winding is coupled between the source and the gate to control a gate-source voltage of the transistor.