Logarithmic Gain Adjuster Using Switchable Digital Stages
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Solution Overview
Problem
Existing digital gain adjusters require complex lookup tables and general-purpose multipliers to convert logarithmic gain control values to linear coefficients, which can be inefficient and require additional components for multiple gain adjustments.
Innovation Solution
A circuit using a cascade of switchable digital gain stages with predetermined multiplication factors, eliminating the need for lookup tables and allowing direct logarithmic multiplication, enabling efficient gain control with reduced complexity and the ability to combine multiple gain adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a linear digital multiplier and lookup table are used to convert logarithmic gain control values to linear coefficients, then gain adjustment functionality is achieved, but device complexity increases due to requiring lookup tables and general-purpose multipliers
Solution Approach 1:
The gain adjustment function is segmented into multiple fixed gain stages (e.g., 0 dB, 3 dB, 6 dB, 9 dB stages) rather than using a single general-purpose multiplier. Each stage is independently controllable via switchable paths, allowing complex gain adjustments to be achieved by combining simpler fixed stages, thereby reducing overall circuit complexity.
Solution Approach 2:
The invention changes the approach from linear coefficient multiplication to logarithmic domain addition. By representing gain values in decibels (logarithmic scale), multiple gain adjustments can be combined through simple addition rather than complex multiplication operations, simplifying the control logic and reducing computational complexity.
2Measurement precision
If lookup tables are used for converting gain control values, then accurate gain control is achieved, but additional components and memory resources are required
Solution Approach 1:
The lookup table component is extracted and eliminated from the system. Instead of storing pre-computed gain coefficients in memory, the invention uses direct analog or digital signal paths with fixed gain stages that physically embody the gain values, removing the need for additional memory components and lookup logic.
Solution Approach 2:
Rather than storing abstract gain coefficient data in lookup tables, the invention creates physical copies of signal paths with predetermined gain characteristics. Each gain stage is a tangible circuit implementation that directly provides the desired gain without requiring data retrieval or conversion.
3Adaptability or versatility
If multiple gain adjustments are applied separately, then comprehensive gain control is achieved, but additional multipliers and control logic are needed
Solution Approach 1:
Multiple gain adjustment functions are merged into a single unified gain control structure. By representing all gain adjustments in the logarithmic domain and using a common set of switchable gain stages, the invention combines what would otherwise require multiple separate multipliers into one integrated circuit, reducing component count and control logic complexity.
Data Source
AI summary
A circuit for multiplying a digital signal by a variable gain, controlled in dependence on a digital gain control value. The circuit comprises: a multiplier input for receiving the digital signal; a multiplier output for outputting the digital signal multiplied by the gain; a plurality of multiplier stages each arranged to multiply by a respective predetermined multiplication factor; and switching circuitry arranged so as to apply selected ones of the multiplier stages in a multiplication path between the input and output, in dependence on the digital gain control value. The multiplication factors are arranged such that binary steps in the digital gain control value result in logarithmic steps in said gain.