Programmable Impedance with Auxiliary Branch for Resolution
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Solution Overview
Problem
In digitally programmable resistors, the incremental difference in resistance decreases as the word length increases, leading to significant impact from switch resistances, particularly in multi-stage architectures, limiting performance and requiring larger integrated circuit area and higher test costs.
Innovation Solution
A programmable impedance system comprising a primary branch and an auxiliary branch, where the primary branch handles a wide range of input values and the auxiliary branch, with switches or controllable impedance, augments the performance by providing lower impedance values, especially at lower input values, thereby reducing the impact of switch resistances and increasing resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the word length or resolution of the digital input increases, then the precision of resistance control improves, but the number of switches and resistors increases exponentially (2^N), increasing device complexity and integrated circuit area
Solution Approach 1:
The resistor string is divided into multiple segments with different resistance values (e.g., R, 2R, 4R, 8R) corresponding to different bit weights. Each segment can be independently controlled by switches, allowing the system to achieve high-resolution resistance control without requiring 2^N switches. The segmentation principle enables efficient encoding of digital input values into analog resistance values.
Solution Approach 2:
The patent implements a multi-stage architecture where coarser resolution stages (handling MSBs) are nested with finer resolution stages (handling LSBs). Each stage processes a portion of the digital input word and combines its output with subsequent stages. This nested structure allows the system to achieve high overall resolution while keeping each individual stage relatively simple, avoiding the exponential growth of components.
2Measurement precision
If the word length increases, then the precision of resistance control improves, but the incremental resistance difference decreases, making switch resistance (Ron) significant and distorting the overall resistance value
Solution Approach 1:
Different segments of the resistor string are assigned different resistance values (R, 2R, 4R, 8R) corresponding to different bit positions. The LSB stage uses smaller resistance values (R) where precision is most critical, while MSB stages use larger resistance values. This local differentiation ensures that switch resistance has minimal impact on the overall accuracy, as the switch Ron becomes a smaller proportion of the total resistance in LSB-critical paths.
Solution Approach 2:
The patent transitions from a single-dimensional resistor string to a multi-dimensional multi-stage architecture. Each stage operates in a different dimensional space of resistance values, with stages handling different bit ranges. This dimensional expansion allows the system to manage the trade-off between incremental resistance difference and switch resistance impact more effectively by distributing the control across multiple dimensions.
3Device complexity
If multi-stage architecture is used, then the number of resistors and switches is reduced, but multiple switches are coupled in series between terminals, limiting performance due to cumulative switch resistance
Solution Approach 1:
The patent implements dynamic switching control where not all switches are active simultaneously for every resistance value. The control logic dynamically selects which switches to activate based on the digital input value, minimizing the number of series-connected switches in the active path. This dynamic approach reduces the cumulative switch resistance effect while maintaining the benefits of multi-stage architecture.
Solution Approach 2:
The control logic预先 determines the optimal switch configuration based on the incoming digital input value. By pre-calculating which switches should be activated before the actual resistance switching occurs, the system can minimize the number of series switches and reduce the impact of switch resistance. This preliminary action ensures that the switch resistance effect is minimized from the outset rather than being a post-hoc correction.
Data Source
AI summary
The present application relates generally to programmable impedances and employs an auxiliary impedance in parallel to a primary programmable impedance to augment the performance of the primary programmable impedance at lower impedance values.