Track-and-Hold Circuit RC Feed-Forward for Low Distortion
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Solution Overview
Problem
High-speed analog-to-digital converters (ADCs) face performance limitations due to harmonic distortion in existing track-and-hold circuits, which affect the accuracy of signal conversion.
Innovation Solution
A track-and-hold circuit design incorporating a bi-directional current source, RC networks, and a unity gain amplifier to reduce signal-dependence of the sampling instant, utilizing additional capacitors to enhance the discharge of transistors and minimize noise bandwidth, and incorporating RC networks to feed-forward the analog input signal and adjust the zero location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If prior art track-and-hold circuits use feedback connection to reduce excess currents, then current flow is improved, but harmonic distortion remains problematic
Solution Approach 1:
The patent extracts and removes the problematic feedback connection from the circuit topology. By eliminating the feedback path that caused harmonic distortion while maintaining the current reduction benefits through alternative circuit configurations, the invention resolves the contradiction between reducing excess current and eliminating harmonic distortion.
Solution Approach 2:
Instead of using feedback to control current flow, the patent inverts the approach by using feed-forward RC networks that proactively shape the signal path. The RC networks are positioned to preemptively correct signal dependencies before they manifest as distortion, reversing the conventional feedback-based control approach.
2Productivity
If track-and-hold circuits sample at regular intervals, then signal conversion is achieved, but signal-dependence of sampling instant causes distortion
Solution Approach 1:
The patent introduces RC networks as intermediary elements between the signal source and the sampling circuit. These RC networks act as mediators that decouple the sampling instant from signal-dependent variations, providing a stable sampling reference that is independent of the input signal characteristics while maintaining high sampling rates.
Solution Approach 2:
The patent changes the electrical parameters of the circuit by introducing specific RC time constants that compensate for signal-dependent variations. By carefully selecting resistor and capacitor values, the circuit transforms the sampling process to maintain precision across varying signal conditions while operating at high speeds.
3Speed
If high-speed ADC performance is improved, then conversion speed increases, but harmonic distortion adversely affects performance
Solution Approach 1:
The patent segments the track-and-hold circuit into distinct functional blocks with specific purposes: feed-forward RC networks for signal conditioning, buffered voltage sources for stable referencing, and isolated sampling switches for clean signal acquisition. This segmentation allows each component to be optimized for high-speed operation while collectively maintaining signal accuracy and minimizing distortion.
Solution Approach 2:
While eliminating problematic feedback paths, the patent introduces controlled feedback mechanisms through the RC networks that provide stability without causing distortion. The RC feedback paths are designed to compensate for high-speed switching effects while maintaining signal fidelity, enabling reliable high-speed conversion.
Data Source
AI summary
A track-and-hold circuit is provided. This track-and-hold circuit is adapted to track an analog input signal and hold a sampled voltage of the analog input signal at a sampling instant for processing by other circuitry, in response to a track signal that alternates with a hold signal. Preferably, the track-and-hold circuit includes a bi-directional current source that sources and sinks current through a first output node and a second output node, a unity gain amplifier that is coupled to first and second output nodes of the bi-directional current source and that receives the analog input signal, a resistor coupled to an output of the unity gain amplifier, and a capacitor coupled between the resistor and ground. Of interest, however, is the bi-directional current source, which includes a differential input circuit that is adapted to receive the track signal and the hold signal and that is coupled to the first and second output nodes and an RC network that is coupled to the differential input circuit. The RC network receives the analog input signal and is scaled to change the location of a zero to reduce the signal-dependence of the sampling instant.