Track-and-Hold Circuit Level Shifter Reduces Charge Injection
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Solution Overview
Problem
Conventional track-and-hold circuits experience significant channel charge injection and channel conductance variation due to the gate-source voltage and threshold voltage variations in response to input signals, affecting the accuracy and stability of analog-to-digital conversion.
Innovation Solution
The implementation of a track-and-hold circuit with level shifters to maintain a constant gate-source voltage of the MOS transistor, using a first and second level shifter to offset the analog input signal by specific DC voltage levels, thereby reducing channel charge injection and conductance variation, and employing a differential buffer to generate a differential output signal pair.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional track-and-hold circuit uses a simple MOS transistor switch without level shifters, then the device complexity is low, but the channel conductance variation and charge injection are significant
Solution Approach 1:
Level shifters are introduced as intermediary circuits between the input signal and the MOS transistor gate. These level shifters translate the input signal voltage levels to maintain a constant gate-source voltage difference, thereby stabilizing the channel conductance and reducing charge injection effects during sampling operations.
Solution Approach 2:
The invention changes the voltage level parameter of the gate signal dynamically using level shifters. By adjusting the gate voltage level to compensate for input signal variations, the gate-source voltage difference remains constant, which stabilizes the channel conductance parameter and reduces the harmful effects of charge injection.
2Ease of operation
If the gate-source voltage varies with the input signal level in a conventional track-and-hold circuit, then the circuit operation is simple, but the channel charge injection increases significantly
Solution Approach 1:
Level shifters serve as intermediary circuits that decouple the input signal voltage variations from the gate-source voltage difference. By introducing these intermediate voltage translation stages, the circuit maintains simple operation while the level shifters actively compensate for voltage variations to keep the gate-source difference constant, thereby reducing charge injection.
Solution Approach 2:
The level shifters perform preliminary compensation by pre-adjusting the gate voltage level before the signal reaches the MOS transistor. This preliminary action counteracts the potential variations in gate-source voltage that would otherwise cause charge injection, effectively preventing the harmful effect before it occurs.
3Reliability
If level shifters are added to maintain constant gate-source voltage, then the channel conductance stability improves, but the device complexity increases
Solution Approach 1:
Level shifters are introduced as intermediary voltage translation circuits that maintain constant gate-source voltage difference. These intermediaries provide the necessary voltage level adjustment to stabilize channel conductance while keeping the overall circuit architecture relatively simple and modular.
Solution Approach 2:
The invention employs parameter changes in the gate voltage level through level shifters to maintain constant gate-source voltage difference. By dynamically adjusting the gate voltage parameter to compensate for input signal variations, the circuit achieves stable channel conductance with a relatively simple approach.
4Device complexity
If the gate-source voltage varies with input signal, then the circuit structure is simple, but the channel conductance variation affects A/D conversion accuracy
Solution Approach 1:
Level shifters are introduced as intermediary circuits that maintain constant gate-source voltage difference, thereby stabilizing channel conductance. This stabilization prevents conductance variation from affecting the accuracy of A/D conversion, while the level shifters themselves are implemented with relatively simple circuit structures.
Data Source
AI summary
An electronic device, such as a sample-and-hold circuit, includes a field effect transistor (FET), a capacitor, and a voltage offset circuit. The FET is configured to receive a signal at a first terminal thereof and selectively provide the signal to a second terminal thereof responsive to a switching signal at a gate terminal thereof. The capacitor is electrically connected to the second terminal of the FET. The voltage offset circuit is electrically connected to the first terminal and the gate terminal of the FET. The voltage offset circuit is configured to maintain a substantially constant voltage differential between the first terminal and the gate terminal of the FET while the signal is provided to the second terminal of the FET and substantially independent of a voltage level of an input signal. Related methods of operation are also discussed.