Correlated Level-Shifting Sampling Switch for Low-Distortion Hold Circuits
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Solution Overview
Problem
Sample and hold circuitry experiences signal distortion due to varying transconductance of transistors in sampling switches, which is not effectively addressed by existing boosting circuits that require significant signal strength and amplifier overhead, limiting their effectiveness in oversampled systems.
Innovation Solution
A sampling switch circuit employing correlated level shifting, which includes a sampling switch, a boosting circuit, and a correlated level shifting buffer circuit with a level shifting capacitor, generates a sampling signal using only one hold phase and one tracking phase, maintaining a constant voltage difference across the sampling switch transistor by level shifting the amplifier output voltage based on a level shifting voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a boosting circuit is used to maintain constant Vgs across the sampling switch, then distortion is reduced, but the circuit requires significant signal strength and amplifier overhead that limits effectiveness in oversampled systems
Solution Approach 1:
The patent changes the voltage parameters dynamically by using a level-shifting capacitor to adjust the control voltage applied to the sampling switch. This allows the circuit to maintain proper operation across different input voltage ranges without requiring excessive amplifier overhead, resolving the contradiction between signal accuracy and energy consumption.
Solution Approach 2:
The level-shifting capacitor acts as an intermediary element between the input signal and the sampling switch control terminal. It mediates the voltage level to ensure the sampling switch operates with appropriate Vgs without requiring the entire signal chain to provide excessive signal strength, thus reducing amplifier overhead while maintaining signal accuracy.
2Adaptability or versatility
If buffer circuits are introduced to drive the boosting circuit, then the circuit can operate with various input signals, but the boosting circuit maintains constant Vgs only for input signals within V_sat of a supply voltage rail
Solution Approach 1:
The patent introduces dynamic voltage level shifting through the level-shifting capacitor that adapts to different input signal ranges. This dynamic adjustment allows the circuit to maintain constant Vgs across a broader input signal range than static boosting circuits, resolving the contradiction between adaptability and precision.
Solution Approach 2:
The voltage control is segmented into multiple manageable components: the main boosting circuit provides the base voltage enhancement, while the level-shifting capacitor provides fine-grained adjustment for different input ranges. This segmentation allows the system to maintain constant Vgs across various input signals without requiring a single complex circuit.
3Device complexity
If the transconductance of the sampling switch transistor varies with input signal magnitude, then the circuit is simpler, but distortion is introduced in the sampled signal
Solution Approach 1:
The level-shifting capacitor serves as an intermediary that compensates for transconductance variations without requiring complex circuit structures. By dynamically adjusting the control voltage, it maintains consistent sampling performance across different signal magnitudes, resolving the contradiction between simplicity and precision.
Solution Approach 2:
The patent uses parameter changes in the control voltage (via the level-shifting capacitor) to compensate for transconductance variations. This allows the simple transistor-based sampling switch to maintain constant effective transconductance across different input signals, achieving high signal accuracy without increasing device complexity.
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 approach minimizes distortion in the sampling switch by maintaining a constant voltage difference across the transistor at any input voltage level, even at maximum and minimum input voltages, thereby improving signal accuracy and reducing amplifier overhead.
Implementation Method 1
a level shifting capacitor having a first terminal and a second terminal... the level shifting capacitor is configured to store a second voltage difference between the second terminal and the third terminal during a first clock phase... the level shifting capacitor is configured to generate the sampling signal at the second terminal
Data Source
AI summary
A sampling switch circuit uses correlated level shifting. The sampling switch circuit includes: a sampling switch having a first terminal, a control terminal, and an output terminal, wherein the first terminal is connected to an input voltage node; a boosting circuit connected to first and second supply voltage nodes and coupled to the control terminal of the sampling switch; and a correlated level shifting buffer circuit. The correlated level shifting buffer circuit includes: an amplifier having first and second inputs and an output, wherein the first input is connected to the input voltage node, and the output and second input are coupled to the boosting circuit; and a level shifting capacitor coupled to the second input and output of the amplifier, to the boosting circuit, and to a level shifting voltage node.