Thermometer-Coded Attenuator With Constant Delay Gain Steps

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Solution Overview

Problem

Conventional attenuator designs face issues with poor monotonicity and phase discontinuity due to binary weighted switching schemes, leading to instability in gain control loops and unacceptable phase variations between adjacent gain states, which are not feasible for high-volume monolithic integration applications.

Innovation Solution

The implementation of a thermometer coded attenuator network that decodes binary weighted steps into thermometer code weighted steps, ensuring monotonicity and reducing phase discontinuity by maintaining a constant signal delay across all attenuation steps, eliminating the need for elaborate trimming approaches.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If binary weighted switching scheme is used to control signal path gain, then the attenuator can provide discrete attenuation steps, but poor monotonicity and phase discontinuity occur

Engineering Contradiction:

Improvediscrete attenuation stepsVSAvoidmonotonicity and phase continuity

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The attenuator is divided into multiple parallel impedance elements (R1, R2, R3, etc.) that can be independently switched. Each element represents a discrete attenuation step, and by selectively switching parallel segments, the attenuator achieves discrete attenuation levels while maintaining signal integrity and phase continuity across all steps.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of using the conventional binary weighted switching scheme that switches series resistors, this patent inverts the approach by using parallel impedance elements where the switched elements are connected in parallel with the signal path. This inversion allows the attenuator to provide discrete attenuation steps while maintaining constant signal delay and phase continuity, resolving the monotonicity and phase discontinuity issues of binary weighted schemes.

Inventive Principle:

Principle #13The other way round (Inversion)

2Ease of operation

If binary weighted switching scheme is used, then attenuation control is achieved, but phase discontinuity occurs between adjacent gain states

Engineering Contradiction:

Improveattenuation controlVSAvoidphase discontinuity

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The parallel impedance elements are designed to maintain equipotential conditions across the signal path. By switching parallel elements rather than series elements, the voltage potential remains consistent across all attenuation steps, ensuring that phase discontinuity is eliminated while still providing effective attenuation control through impedance variation.

Inventive Principle:

Principle #12Equipotentiality

Solution Approach 2:

The parallel impedance configuration ensures continuous signal flow through the attenuator regardless of which attenuation step is selected. The signal always passes through a continuous path with consistent electrical characteristics, eliminating phase discontinuities between adjacent gain states while maintaining the ability to control attenuation levels.

Inventive Principle:

Principle #20Continuity of useful action

3Ease of operation

If conventional attenuator designs are used, then discrete attenuation is provided, but elaborate trimming processes are required

Engineering Contradiction:

Improvediscrete attenuationVSAvoidtrimming processes

Core Design Contradiction:

Ease of operationVSEase of manufacture

Solution Approach 1:

The parallel impedance element configuration provides self-aligning electrical characteristics that automatically ensure proper attenuation levels without requiring external trimming. The inherent symmetry and parallel structure of the circuit cause the attenuation steps to naturally align, eliminating the need for elaborate trimming processes and enabling high-volume monolithic integration.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

By changing the fundamental circuit parameter from series resistance switching to parallel impedance switching, the patent eliminates the need for trimming. The parallel configuration inherently provides the desired attenuation characteristics through impedance transformation, allowing discrete attenuation to be achieved without manual or automated trimming processes.

Inventive Principle:

Principle #35Parameter changes

4Ease of operation

If binary weighted switching is used, then attenuation steps are provided, but signal delay varies across attenuation steps

Engineering Contradiction:

Improveattenuation stepsVSAvoidsignal delay variance

Core Design Contradiction:

Ease of operationVSLoss of time

Solution Approach 1:

The parallel impedance elements are designed to provide multiple functions simultaneously: attenuation control and constant signal delay. Each parallel element is configured to contribute to both attenuation and time delay in a unified manner, ensuring that as attenuation changes, the signal delay remains constant across all steps, achieving multi-functionality in a single circuit architecture.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS7911293B2Thermometer coded attenuator

Publication Date: 2011.03.22 BAE SYSTEMS INFORMATION ANDELECTRONIC SYSTEMS INTEGRATION INC

AI summary

Techniques are disclosed that allow for programmable attenuation using thermometer code steps. By thermometer coding the attenuator structure, monotonicity is guaranteed or otherwise greatly improved, which eliminates instability problems with automatic gain control loops and without the need for compensation or trimming. In addition, the thermometer coding technique also greatly reduces phase discontinuity between adjacent gain states.