Sample-Hold Circuit Voltage Clamping Above Supply Rails
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Solution Overview
Problem
Conventional sample/hold circuits malfunction when input voltage levels exceed the power supply voltage, causing the sample/hold circuit to fail in holding the signal accurately due to forward-biased p-n junctions.
Innovation Solution
Incorporating a pass transistor and a high voltage generator that applies a voltage exceeding the power supply voltage to the control terminal of the pass transistor, ensuring the voltage level is clamped within the safe range, and using a complementary switch configuration to manage rail-to-rail signal swings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional sample/hold circuit is used without high voltage protection, then the circuit structure remains simple, but the circuit malfunctions when input voltage exceeds power supply voltage due to forward-biased p-n junctions
Solution Approach 1:
A pass transistor is introduced as an intermediary component between the input signal and the sample/hold circuit. This pass transistor acts as a protective mediator that prevents high voltage from reaching the vulnerable p-n junctions in the conventional sample/hold circuit, thereby resolving the contradiction between maintaining circuit simplicity and improving reliability under high voltage conditions.
Solution Approach 2:
The pass transistor provides beforehand protection by clamping the input voltage before it can cause damage to the sample/hold circuit. This prior cushioning mechanism ensures that even when high voltage signals are present, the downstream circuit components remain protected, thus improving reliability without requiring complex redesign of the entire sample/hold circuit.
2Adaptability or versatility
If a pass transistor with high voltage generator is added to protect against high voltage, then the circuit can handle voltages exceeding supply voltage, but the device complexity increases
Solution Approach 1:
The pass transistor serves multiple functions: it acts as a protective element against high voltage, functions as a signal transmission path during normal operation, and enables the circuit to adapt to a wider voltage range. By making this single component multi-functional, the patent achieves voltage range adaptability without proportionally increasing overall circuit complexity.
3Measurement precision
If the sampling switch directly connects to the capacitor without voltage clamping, then the circuit operation is simple, but the voltage holding accuracy deteriorates when input voltage exceeds supply voltage
Solution Approach 1:
The pass transistor performs preliminary voltage clamping action before the signal reaches the sampling switch and capacitor. By pre-processing the input signal to remove excessive voltage components, the circuit maintains accurate voltage holding capability during the sampling phase, resolving the contradiction between simple operation and precise measurement under high voltage conditions.
Data Source
AI summary
A sample/hold circuit module. The sample/hold circuit module comprises a sample/hold circuit, an S/H controller, a pass transistor, and a high voltage generator. The sample/hold circuit comprises a capacitor and a sampling switch. The capacitor has a first electrode coupled to a first fixed voltage and a second electrode coupled to an output node of the sample/hold circuit module. The sampling switch comprises an output terminal coupled to the second electrode of the capacitor, an input terminal, and a control terminal. The S/H controller is coupled between the control terminal of the sampling switch and a second fixed voltage. The pass transistor has a sampling input terminal, an output terminal coupled to the input terminal of the sampling switch, and a control terminal. The high voltage generator is coupled between the control terminal of the pass transistor and the second fixed voltage.