Track-and-Hold Circuit RC Zero Shift 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 their 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, an RC network, and a unity gain amplifier, with additional capacitors and resistors to reduce signal-dependence of the sampling instant and minimize harmonic distortion, is implemented.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional track-and-hold circuit is used, then the ADC can operate at high speed, but harmonic distortion occurs that degrades performance
Solution Approach 1:
An RC network is introduced as an intermediary element between the signal source and the track-and-hold circuit. This RC network modifies the signal path to reduce signal-dependence of the sampling instant, thereby minimizing harmonic distortion while preserving high-speed operation capability
Solution Approach 2:
The circuit employs parameter changes by scaling the RC network components to specifically alter the location of a zero in the transfer function. This parameter adjustment reduces signal-dependence effects and harmonic distortion without compromising the high-speed sampling performance
2Loss of energy
If feedback connection is used to reduce excess currents, then current flow is improved, but harmonic distortion problems persist
Solution Approach 1:
The RC network serves as an intermediary that addresses the harmonic distortion issue that persists even when feedback connections are used for current management. By modifying the signal path characteristics, it reduces signal-dependence effects that cause distortion
3Object-generated harmful factors
If signal-dependence of sampling instant is reduced, then harmonic distortion decreases, but circuit complexity increases
Solution Approach 1:
A relatively simple RC network is introduced as an intermediary element to reduce signal-dependence of the sampling instant. This approach achieves harmonic distortion reduction with minimal added circuit complexity, as the RC network consists of basic passive components
Solution Approach 2:
By scaling existing RC network components to change the location of a zero in the transfer function, the circuit achieves reduced signal-dependence and harmonic distortion without requiring fundamentally new circuit topologies, thus limiting the increase in complexity
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.