Track-and-Hold Gate Buffering Without Bootstrap Complexity
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Solution Overview
Problem
Track and hold circuits face challenges in balancing high speed, large bandwidth, and linearity, particularly when using MOS transistors as pass gates, due to modulation of on-resistance with the input signal, which requires maintaining a constant gate-source voltage independently of the input signal.
Innovation Solution
A track and hold circuit is implemented using a buffer circuit to generate the gate voltage for the main transistor, supplied by a second set of voltage rails with a greater voltage swing than the main transistor circuit, eliminating the need for bootstrap techniques and allowing the gate voltage to exceed the supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If bootstrap techniques are used to generate gate voltage, then the gate voltage can exceed supply voltage and maintain constant gate-source voltage, but the circuit complexity increases due to additional bootstrap capacitors and switches
Solution Approach 1:
The patent extracts the voltage swing requirement from the main transistor circuit and assigns it to a separate buffer circuit supplied by dedicated second voltage rails. This separation eliminates the need for bootstrap capacitors and switches, removing the complex voltage generation mechanism while preserving the constant gate-source voltage effect that ensures linearity.
Solution Approach 2:
The patent segments the voltage supply system into two independent sets: first voltage rails for the main transistor circuit and second voltage rails with greater swing for the buffer circuit. This segmentation allows the buffer to provide the necessary voltage headroom without requiring complex bootstrap circuitry, simplifying the overall design while maintaining performance.
2Manufacturing precision
If the gate voltage is kept constant relative to input voltage, then linearity is improved, but the voltage headroom requirement may exceed available supply voltage
Solution Approach 1:
The patent introduces a new dimension in the voltage supply system by implementing a second set of voltage rails with greater swing specifically for the buffer circuit. This dimensional expansion in the voltage domain provides the necessary headroom for maintaining constant gate-source voltage without being constrained by the limited first supply voltage, thereby preserving linearity.
3Ease of operation
If bootstrap capacitors and switches are used, then gate voltage control is achieved, but charge injection and input loading increase
Solution Approach 1:
The patent removes the bootstrap capacitors and switches from the circuit, extracting the voltage control function and relocating it to a buffer circuit supplied by second voltage rails. This elimination of reactive components directly eliminates the charge injection problem while maintaining effective gate voltage control through the buffer's voltage amplification capability.
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
This solution achieves improved linearity, reduced charge injection, and efficient transition times without the complexity of bootstrap circuitry, suitable for high-speed applications like analog-to-digital converters and multiplexer circuits.
Implementation Method 1
a buffer circuit for generating a gate voltage for turning on the main transistor during a track phase, wherein the buffer circuit is adapted to derive a gate voltage based on the input or output voltage of the circuit and a voltage step
Implementation Method 2
a storage capacitor for storing the output voltage during a hold phase during which the main transistor is turned off
Data Source
Figure 1~2
Figure 3~4b
Figure 5a~5b
AI summary
A track and hold circuit has a main transistor (10) for which the gate voltage is provided by a buffer circuit (B1) which is supplied with a different voltage supply than the circuit of the main transistor. This avoids the need for a bootstrap circuit.