Track-and-Hold Circuit Gate Control for Low-Nonlinearity Sampling
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Solution Overview
Problem
Existing track and hold circuits are insufficient for meeting high-resolution and high-speed video applications due to nonlinear operation caused by varying on resistance and channel charge, which degrades the signal-to-noise-and-distortion ratio (SNDR).
Innovation Solution
A wideband track and hold circuit is designed with a track-voltage generating device that supplies a constant control voltage to the switch device during the track phase, maintaining consistent channel charge and on resistance, and includes a buffer device to improve linearity, utilizing MOS transistors for efficient threshold-voltage matching and minimal hardware addition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple switch device is used in the track and hold circuit, then the circuit area is small and implementation is simple, but the on resistance and channel charge vary with the input signal causing nonlinear operation and degraded SNDR
Solution Approach 1:
The patent changes the voltage parameter applied to the gate terminal of the switch device. Instead of using a fixed voltage level, the invention applies a dynamically adjusted voltage that compensates for the nonlinear characteristics of the switch device, thereby maintaining consistent channel charge and on resistance across different input signal levels.
Solution Approach 2:
The patent implements a feedback mechanism where the actual voltage level at the gate terminal is monitored and used to adjust the control voltage. This feedback loop ensures that the channel charge remains constant despite variations in input signal, thereby improving linearity and SNDR while maintaining a relatively simple circuit structure.
2Productivity
If existing track and hold circuits are used, then the current design is sufficient for 8-bit resolution at 270 Msamples/s, but they cannot meet the requirements for 12-bit resolution and 400 Msamples/s or higher
Solution Approach 1:
The patent introduces dynamic voltage adjustment to the switch device operation. The control voltage is no longer static but dynamically adapted during the track phase to maintain optimal switching characteristics across the entire bandwidth required for high-speed operation, enabling both higher sample rates and improved resolution.
Solution Approach 2:
The patent modifies the electrical parameters of the switch device by applying a dynamically adjusted voltage level that changes with the input signal characteristics. This parameter adjustment ensures that the switch device maintains consistent performance across the extended bandwidth required for 400 Msamples/s and higher, while also improving linearity for 12-bit resolution.
3Measurement precision
If a constant control voltage is applied to the switch device, then the channel charge varies with input signal causing nonlinear settling, but adjusting the voltage dynamically adds circuit complexity
Solution Approach 1:
The patent employs a feedback-based voltage adjustment mechanism that automatically compensates for nonlinearities without requiring complex external control circuits. The feedback signal is derived from the existing circuit nodes, and the adjustment is performed using additional switch devices that are already part of the track and hold structure, thereby improving linearity with minimal added complexity.
Solution Approach 2:
The patent enables the track and hold circuit to self-correct its nonlinearities through internal feedback mechanisms. The circuit uses its own operating parameters to generate the correction signal, eliminating the need for external complex control circuits and maintaining implementation simplicity while achieving improved linearity.
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 solution achieves low nonlinearity and improved SNDR with minimal hardware and power dissipation, suitable for high-speed and high-resolution applications like video processing, by ensuring constant channel charge and on resistance through precise voltage control and matching of MOS transistors.
Implementation Method 1
a capacitive hold device (20) connected to a second terminal of the switch device (10)
Data Source
AI summary
A track and hold circuit (1) comprising a switch device (10) and a capacitive hold device (20). The track and hold circuit (1) comprises a track-voltage generating device (30) adapted to generate a control voltage based on a signal on an input terminal of the switch device (10) and supply the control voltage to the switch device (10) during track phases of the track and hold circuit (1). The control voltage provides a channel charge, which is the same for each track phase, in the switch device (10).