MDAC Capacitor-Resistor Scaling for Higher Multiplying Bandwidth
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Solution Overview
Problem
Multiplying digital to analog converters (MDACs) face limitations in multiplying bandwidth due to parasitic capacitance from resistor ladders, board traces, and amplifier input capacitance, which degrades stability and limits bandwidth without increasing power dissipation.
Innovation Solution
Incorporating an array of capacitors scaled in inverse proportion to resistors, allowing selective coupling to output current nodes based on the MDAC code, altering the transfer function to increase multiplying bandwidth without increasing power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an array of capacitors scaled in inverse proportion to resistors is incorporated into the MDAC, then multiplying bandwidth is increased, but device complexity increases
Solution Approach 1:
The MDAC is segmented into multiple capacitor elements (first, second, third, and fourth capacitors) with different capacitance values, where each capacitor is selectively coupled to the output current node based on the MDAC code. This segmentation allows the system to achieve higher bandwidth by providing multiple parallel current paths while maintaining manageable complexity through modular design.
Solution Approach 2:
The capacitor array is dynamically controlled through switching mechanisms that selectively couple specific capacitors to the output current node based on the MDAC code. This dynamic configuration allows the system to adapt its capacitance values in real-time, optimizing bandwidth performance without permanently increasing complexity across all operating conditions.
2Speed
If the capacitor array is selectively coupled based on MDAC code, then transfer function is altered to increase bandwidth, but manufacturing precision requirements increase
Solution Approach 1:
Different capacitors in the array are assigned specific capacitance values (first capacitor with first capacitance value, second capacitor with second capacitance value, etc.) that are scaled in inverse proportion to their corresponding resistors. This local differentiation of capacitance values allows precise control over the transfer function and bandwidth characteristics while enabling manufacturing tolerances to be managed on a component-by-component basis rather than requiring uniform precision across the entire system.
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 doubles the multiplying bandwidth of the MDAC while maintaining a flat passband response and reducing power dissipation, achieving improved performance without increasing the MDAC's power consumption or area.
Implementation Method 1
An array of capacitors scaled in inverse proportion to resistors in the MDAC. Each capacitor in the array of capacitors is selectively coupled to an output current node based on the portion of MDAC code
Data Source
AI summary
A multiplying digital to analog converter (MDAC) includes a first resistor configured to be selectively connected to a current output node based on a first bit of a first portion of an input digital code and a second resistor configured to be selectively connected to the current output node based on a second bit of the first portion of the input digital code. A resistance of the second resistor is a resistance of the first resistor scaled by a factor. The MDAC further includes a first capacitor configured to be selectively connected to the current output node based on the first bit of the first portion and a second capacitor configured to be selectively connected to the current output node based on the second bit of the first portion. A capacitance of the second capacitor is a capacitance of the first capacitor scaled by an inverse of the factor.