Bootstrapped Switch Bulk Biasing for Low-Leakage Voltage Swing
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Solution Overview
Problem
Field-effect transistors used as switches in analog circuits exhibit input-dependent on-resistance, leading to distortion and increased power consumption due to forward biasing of source/drain-bulk junctions, which is undesirable for energy-efficient devices.
Innovation Solution
A bootstrapped switch with dynamic bulk biasing and an internal delay line is implemented to prevent forward biasing of the source-bulk junction and provide non-overlapping signals, reusing existing circuitry and avoiding separate non-overlapping signal generation circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bootstrapped switch uses a transistor connecting voltage supply to a capacitor, then the switch can provide voltage swing capability, but the drain-bulk junction becomes forward biased during switch-off transition causing increased leakage and power consumption
Solution Approach 1:
An intermediary transistor (third transistor) is introduced between the voltage supply and the bulk terminal of the second transistor. This intermediary transistor acts as a mediator that prevents direct forward biasing of the drain-bulk junction by controlling the bulk voltage independently, thereby reducing leakage current and power consumption during switch-off transition
2Device complexity
If the drain-bulk junction is allowed to become forward biased, then the circuit can simplify, but transistor leakage increases and power consumption rises
Solution Approach 1:
The third transistor serves as an intermediary element that adds minimal circuit complexity while effectively preventing energy loss. By controlling the bulk terminal voltage through this intermediary device, the circuit avoids significant leakage currents without requiring major structural changes
3Reliability
If a separate non-overlapping signal generation circuit is added, then non-overlapping control signals can be provided, but device complexity increases
Solution Approach 1:
The existing internal delay line circuit is made multi-functional by configuring it to generate non-overlapping control signals in addition to its original function. This universal approach allows the same circuit structure to serve multiple purposes: providing delayed signals and generating non-overlapping control signals, thereby avoiding the need for separate dedicated circuitry
Data Source
AI summary
In an integrated circuit, a bootstrapped switch includes a capacitor and first, second, and third transistors. The first transistor has a first current electrode coupled to a first voltage supply node and a gate electrode coupled to a first circuit node. The second transistor has a first current electrode coupled to a second voltage supply terminal, a second current electrode coupled to a top terminal of the capacitor, and a control electrode coupled to the first circuit node. The third transistor has a first current electrode coupled to the first voltage supply terminal, a control electrode coupled to the first circuit node, and a second current electrode coupled to a body terminal of the second transistor. The fourth transistor has a first current electrode coupled to the body terminal of the second transistor, and a second current electrode coupled to the top terminal of the capacitor.