Isolated Bipolar Sampling Network for ADC Inputs Beyond Supply Voltage
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Solution Overview
Problem
Existing sampling networks for differential input signals in ADCs face limitations in noise linearity, power consumption, and the ability to sample signals beyond the power supply voltage, as they rely on resistive dividers and buffer amplifiers, and are unable to handle signals outside the power supply range.
Innovation Solution
A bipolar isolated sampling network that uses a polarity comparator and sampling switches operating as rectifiers to sample differential signals between -V DSMAX and V DSMAX, eliminating the need for resistive dividers and buffer amplifiers, and employing charge pumps to control the gate voltage of sampling switches, allowing sampling beyond the supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If resistive dividers and buffer amplifiers are used to limit differential voltage at ADC input terminals, then the voltage swing is limited to close to supply voltages, but the circuit can handle signals within the supply voltage range
Solution Approach 1:
The patent removes resistive dividers and buffer amplifiers from the circuit. Instead of using these traditional components to limit voltage swing, the invention uses isolated sampling switches that can directly handle bipolar differential signals beyond the supply voltage range, thereby extracting the unnecessary voltage limiting function and replacing it with a more versatile switching mechanism.
Solution Approach 2:
The patent changes the operating parameters of the sampling switches by using isolated switches with controlled gate voltages. This allows the switches to operate in a mode where they can pass signals beyond the supply voltage range without requiring traditional voltage limiting components, effectively changing the voltage handling capability from supply-voltage-limited to isolation-limited.
2Use of energy by moving object
If resistive dividers and buffer amplifiers are used in the sampling network, then power consumption increases, but the circuit can provide voltage buffering
Solution Approach 1:
The patent extracts and removes the buffer amplifier component from the circuit. The isolated sampling switches inherently provide the necessary buffering function without requiring a separate buffer amplifier stage, thereby eliminating the continuous power consumption associated with buffering while maintaining signal integrity through the switching mechanism.
Solution Approach 2:
The patent uses periodic sampling action instead of continuous buffering. The isolated sampling switches operate in a periodic manner, conducting only during the sampling phase and remaining non-conducting during other phases. This periodic operation eliminates the continuous power consumption of buffer amplifiers while still providing effective signal transfer during the required sampling intervals.
3Measurement precision
If traditional sampling networks are used, then noise and linearity are degraded, but the circuit structure is simpler
Solution Approach 1:
The patent uses isolated sampling switches that create isolated copies of the input signal for each phase of operation. This isolation prevents noise coupling and interference between different signal paths and phases, thereby improving noise performance and linearity. The isolated switches effectively copy the signal function while maintaining electrical isolation that traditional shared-component architectures cannot provide.
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 improved noise and linearity, reduced power consumption, and extended sampling range without resistive dividers or buffer amplifiers, enabling accurate sampling of signals far beyond the power supply voltage with lower aging and drift.
Implementation Method 1
sampling switches that operate as rectifiers to sample differential signals between -VDSMAX and VDSMAX
Implementation Method 2
employing charge pumps to control the gate voltage of sampling switches, allowing sampling beyond the supply voltage
Data Source
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AI summary
A method and a circuit achieve fully isolated sampling of bipolar differential voltage signals. The isolated sampling network is suitable for applications in which sampling signals far outside of the supply voltages are desired. A sampling network of the present invention may sample a differential signal between voltages -VDSMAX and VDSMAX, even with common mode voltages that exceed the supply voltage (e.g., an input stage of an ADC). The bipolar isolated input sampling network may include a polarity comparator and sampling switches that operate as rectifiers. Rectification ensures that a unipolar sampling network needs only to sample signals of predetermined voltage levels.