Differential Bootstrapped Track-and-Hold With Charge Injection Cancellation

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Solution Overview

Problem

Track-and-hold circuits face performance limitations due to the on-resistance of sampling transistors and charge injection errors caused by bootstrap drivers, which degrade the linearity of the output signal.

Innovation Solution

A differential bootstrapped track-and-hold circuit is introduced, comprising two single-ended bootstrapped track-and-hold circuits with dummy switches and capacitors to compensate for charge injection errors, ensuring improved switch linearity by connecting dummy output terminals across each other via capacitors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a bootstrap driver circuit is used to establish low on-resistance of the sampling transistor, then switch linearity is improved, but charge injection errors occur when the sampling transistor is turned off

Engineering Contradiction:

Improveswitch linearityVSAvoidcharge injection errors

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

A dummy sampling transistor is introduced as an intermediary element that replicates the charge injection behavior of the main sampling transistor. The dummy transistor is connected to a dummy output node that is then coupled to the main output through a capacitor, allowing the charge injection errors to be compensated without affecting the main signal path.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The charge injection error, which is normally a harmful effect, is converted into a useful compensation signal. By using the dummy sampling transistor to generate an identical charge injection error and then subtracting it from the main output, the harmful effect is transformed into a mechanism for error cancellation and improved linearity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Reliability

If the injected charge is dependent on the input signal, then charge injection compensation becomes necessary, but linearity performance degradation occurs

Engineering Contradiction:

Improvecharge injection compensationVSAvoidlinearity performance

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The dummy sampling transistor creates a copy of the charge injection effect produced by the main sampling transistor. By replicating the exact same charge injection behavior and then subtracting this copy from the main output signal, the linearity performance is maintained even when charge injection is signal-dependent.

Inventive Principle:

Principle #26Copying

3Device complexity

If a single-ended bootstrapped track-and-hold circuit is used, then circuit simplicity is maintained, but charge injection errors cannot be compensated

Engineering Contradiction:

Improvecircuit simplicityVSAvoidcharge injection errors

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The track-and-hold circuit is segmented into two parallel paths: a main path with the sampling transistor for signal acquisition and a dummy path with the dummy sampling transistor for charge injection compensation. This segmentation allows independent optimization of each path while maintaining overall circuit functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The main sampling path and the dummy compensation path are merged into a single differential structure. The outputs of both paths are combined through capacitive coupling, allowing the beneficial signal from the main path and the compensating signal from the dummy path to work together to eliminate charge injection errors.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20220416785A1Differential bootstrapped track-and-hold circuit with cross-coupled dummy sampling switches

Publication Date: 2022.12.29 NXP USA INC

AI summary

Embodiments of a differential bootstrapped track-and-hold circuit are disclosed. In an embodiment, the differential bootstrapped track-and-hold circuit includes first and second single-ended bootstrapped track-and-hold circuits. Each single-ended bootstrapped track-and-hold circuit includes a sampling switch connected between an input terminal and an output terminal, a sampling capacitor connected to the output terminal, and a dummy sampling switch connected between the input terminal and a dummy output terminal. The sampling switch and the dummy sampling switch are controlled by a bootstrap driver connected to the input terminal. The dummy output terminal of the first single-ended bootstrapped track-and-hold circuit is connected to the output terminal of the second single-ended bootstrapped track-and-hold circuit and the dummy output terminal of the second single-ended bootstrapped track-and-hold circuit is connected to the output terminal of the first single-ended bootstrapped track-and-hold circuit to provide signals to compensate for charge injection errors at the output terminals.