Isolated Bipolar Sampling Network for Over-Supply Differential Signals
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Solution Overview
Problem
Existing sampling networks, such as those in analog-to-digital converters, are unable to sample differential input signals that exceed the power supply voltages due to the lack of charge pumps, resulting in limited sampling range and potential sampling errors.
Innovation Solution
A bipolar isolated sampling network that includes a polarity comparator and sampling switches operating as rectifiers, allowing the sampling of differential signals between -VDSMAX and VDSMAX, even with common mode voltages exceeding the supply voltage, by using charge pumps to control the gate voltage of sampling switches and incorporating a rectifier circuit to ensure unipolar sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If charge pumps are not used for controlling the input sampling network, then the circuit is simpler, but the sampling range is limited to power supply voltages
Solution Approach 1:
The sampling network is divided into multiple independent sampling switches (S1, S2, S3, S4) that can be controlled independently by charge pumps. Each switch handles a specific portion of the sampling function, allowing the system to achieve extended sampling range while maintaining manageable complexity through modular design.
Solution Approach 2:
Charge pumps are introduced as intermediary devices between the control logic and the sampling switches. These charge pumps generate the necessary gate voltages to control the sampling switches, enabling the system to sample signals beyond the power supply voltages without requiring direct high-voltage control signals.
2Reliability
If resistive dividers and buffer amplifiers are used to limit differential voltage, then the ADC input voltage is protected, but power consumption increases and aging drift occurs
Solution Approach 1:
The harmful components (resistive dividers and buffer amplifiers) are completely removed from the signal path. Instead of using these traditional voltage-limiting components, the invention uses isolated sampling switches controlled by charge pumps to directly sample the differential signal, eliminating the sources of power consumption, aging, and drift associated with resistive and amplifying components.
Solution Approach 2:
The passive resistive voltage division and active buffering approach is replaced with an isolated switching approach. The sampling switches act as ideal connectors that can be opened or closed without introducing the continuous power consumption and non-ideal characteristics of resistive dividers and buffer amplifiers.
3Ease of manufacture
If the sampling network is designed to sample signals within power supply voltages, then the circuit design is simpler, but signals far outside supply voltages cannot be sampled
Solution Approach 1:
The sampling network uses dynamically controlled switches whose on/off states are determined by the sampling phase. The charge pumps dynamically adjust the gate voltages of the sampling switches based on the sampling timing, enabling the system to adapt to signals of various amplitudes and polarities while maintaining a relatively simple static circuit structure.
Solution Approach 2:
The charge pumps change the voltage parameters (gate voltages) of the sampling switches to enable them to handle signals beyond the power supply voltages. By dynamically adjusting the gate voltages, the switches can operate correctly even when the sampled signals exceed the nominal power supply range, effectively expanding the sampling capability without fundamentally changing the circuit topology.
Data Source
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.