DAC Output Capacitor Buffering for Low-Noise Signal Generation
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Solution Overview
Problem
Conventional charge redistribution DA converters generate noise such as refresh noise, charge injection, and clock feedthrough when switching between modes, leading to less accurate output voltages and limitations on the size and capacitance of the capacitor array due to thermal noise and non-linear voltage dependency on gate capacitance.
Innovation Solution
A signal generating apparatus with a DA converter, a capacitor section, and a transmission switch, where the control section alternates between refresh and output modes to charge the capacitor section, filtering noise and matching the voltage to the input data, allowing for increased capacitance and accuracy while maintaining a smaller capacitor array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the overall capacitance of the capacitor array is reduced to decrease area, then the area is reduced, but thermal noise (KT/C noise) increases
Solution Approach 1:
A capacitor section is introduced as an intermediary element between the DA converter and the output. This capacitor section acts as a mediator that filters thermal noise while allowing the main capacitor array to maintain reduced capacitance and area. The intermediary capacitor provides the necessary noise filtering capability without requiring the main capacitor array to be large.
Solution Approach 2:
The noise filtering function is extracted from the main capacitor array by separating it into two functional parts: the DA converter's capacitor array for voltage generation and a separate capacitor section for noise filtering. This extraction allows the main array to be minimized for area while the separate capacitor handles the noise filtering responsibility.
2Loss of energy
If switching between refresh mode and output mode is performed to generate output voltage, then power consumption is reduced, but noise such as refresh noise, charge injection, and clock feedthrough is generated
Solution Approach 1:
The capacitor section serves as a buffer intermediary between the switching DA converter and the output. It absorbs and filters the switching noise (refresh noise, charge injection, clock feedthrough) generated during mode transitions, preventing these harmful factors from appearing at the output while allowing the efficient switching operation to continue.
Solution Approach 2:
The capacitor section utilizes the switching noise energy by filtering it through its capacitance, converting the harmful switching transients into smooth voltage transitions. The noise energy that would otherwise degrade output accuracy is instead used to charge/discharge the capacitor section in a controlled manner, ultimately producing a clean output voltage.
3Area of stationary object
If a low-capacitance capacitor is realized by gate capacitance of a transistor to reduce area, then area is reduced, but non-linear voltage dependency on gate capacitance reduces accuracy
Solution Approach 1:
The capacitor section acts as a linearizing intermediary that compensates for the non-linear voltage dependency of transistor gate capacitance. By providing a stable, linear capacitive element in series with the DA converter output, it smooths out the non-linearities and maintains accurate voltage output across the full signal range.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively filters noise, reduces thermal noise, and achieves accurate output voltages with a smaller capacitor array, enabling a more precise and efficient signal generation process.
Implementation Method 1
a capacitor section 22 that is provided between the output end 12 and a standard potential
Data Source
AI summary
Provided is a signal generating apparatus that outputs from an output end thereof an output voltage corresponding to input data supplied thereto, comprising: a DA converter that outputs a voltage corresponding to data supplied thereto; a capacitor section that is provided between the output end and a standard potential; a transmission switch that provides a connection or a disconnect between a voltage generating end of the DA converter and the output end; and a control section that causes the DA converter to charge the capacitor section with a voltage corresponding to the input data by repeatedly connecting and disconnecting the transmission switch, thereby causing the voltage of the capacitor section to gradually approach the output voltage corresponding to the input data.