Programmable Resistor Network for Linear-in-dB Gain Control
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Solution Overview
Problem
Existing digitally-controlled resistor circuits face challenges in achieving wide-range programmability with linear-in-dB control, as they often require additional active stages that increase power dissipation, noise, and distortion, and are not suitable for logarithmic control.
Innovation Solution
A programmable resistor circuit that includes multiple programmable resistor cells connectable in parallel, with a decoder circuit to select groups of cells for establishing non-overlapping resistance subranges with equal logarithmic increments, allowing for a wide range of resistance values with linear-in-dB control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If additional active stages are used for coarser steps in programmable-gain amplifiers, then the programmable gain range is improved, but power dissipation, noise, and distortion increase
Solution Approach 1:
The feedback resistor is divided into multiple discrete resistor elements (R1, R2, R3, R4) that can be individually switched into the circuit. This segmentation allows the gain to be programmed in discrete steps without requiring additional active stages, thereby avoiding the associated power dissipation, noise, and distortion while still achieving a wide programmable gain range from 1.0 to 16.0.
2Device complexity
If R-2R or power-of-2 resistor networks are used for filtering, then the circuit structure is simplified, but logarithmic control capability is lost
Solution Approach 1:
The patent applies different resistor value relationships to different parts of the resistor network to achieve both simplicity and logarithmic control. Specifically, the resistors are configured such that R2 = 2×R1, R3 = 4×R1, and R4 = 8×R1, creating local geometric progressions that collectively enable logarithmic gain control when switched in parallel, while maintaining a relatively simple overall circuit structure.
3Adaptability or versatility
If capacitors are used in conjunction with resistor networks such as R-2R for filtering, then filtering functionality is added, but the circuit becomes unwieldy and requires more active stages
Solution Approach 1:
The patent combines the gain control function and the filtering function into a single integrated circuit structure. The same set of discrete resistor elements that provide programmable gain also work in conjunction with a single capacitor to provide filtering. This merging eliminates the need for separate active stages for filtering, keeping the circuit simple while achieving both functions simultaneously.
Data Source
AI summary
A programmable resistor can provide discrete logarithmic (linear-in-dB) gain control. It can include multiple like programmable resistor subnetworks or cells, such as can be connected in parallel, such as according to a decoding scheme. The subnetworks can be configured to cover a subrange such as [0 dB, −6 dB) relative to the maximum resistance value. Coarse increments of −6 dB can be further added to this range by successively doubling the number of subnetworks that are connected in parallel. An additional decoder help ensure a linear control curve, free of dead zones or other nonlinearities. The programmable resistor can be suitable for use in such circuits as programmable-gain amplifiers, filters, or more complex networks, such as where the resistance can be programmed as a function of a digital code. An example including a tuning circuit for a variable gain active filter is described.