Positive Voltage Pi-Type Attenuator Eliminates DC Block Capacitors

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Solution Overview

Problem

Conventional π-type voltage-controlled variable attenuators in GaAs integrated circuits face challenges due to the need for negative control voltages, which are not compatible with standard positive supply voltages, and the presence of DC block capacitors that inhibit operation at low frequencies and consume significant chip area, while also being prone to electrostatic discharge.

Innovation Solution

A π-type positive voltage-controlled variable attenuator design that eliminates DC block capacitors between the series and shunt arms, using resistive components and a resistor biasing subcircuit to control the attenuation with positive voltages, allowing for variable attenuation across a wide frequency range without internal capacitors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If DC block capacitors are used to isolate series and shunt arms in conventional π-type attenuators, then the attenuator can be implemented with depletion mode FETs using positive control voltages, but the capacitors inhibit operation at low frequencies and consume significant chip area

Engineering Contradiction:

Improvefrequency rangeVSAvoidchip area

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent removes DC block capacitors from the circuit by reconfiguring the attenuator to use resistive isolation between series and shunt arms. This extraction eliminates the frequency limitations and chip area consumption associated with large capacitor structures while maintaining the ability to provide variable attenuation across a wide frequency range including low frequencies.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the isolation mechanism from capacitive to resistive, fundamentally altering the electrical parameters of the circuit. By using resistors instead of capacitors for isolation, the circuit achieves low-frequency operation capability while reducing chip area, as resistive elements occupy significantly less space than the large capacitors required for low-frequency blocking.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If DC block capacitors are used in the attenuator circuit, then proper DC isolation is achieved, but the capacitors are prone to electrostatic discharge damage

Engineering Contradiction:

Improveelectrostatic discharge resistanceVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces fragile capacitive isolation elements with robust resistive elements that are inherently more resistant to electrostatic discharge. Resistors are simpler, more durable components that can withstand ESD events without damage, thereby improving reliability while reducing circuit complexity through the elimination of capacitor-related protection circuits.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of operation

If depletion mode FETs are used as passive components in GaAs IC attenuators, then variable attenuation is achieved, but negative control voltages are required which are incompatible with standard positive supply voltages

Engineering Contradiction:

Improvecontrol voltage compatibilityVSAvoidbias circuit

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent inverts the control mechanism by using positive control voltages applied to the gates of depletion mode FETs in the shunt arms, rather than requiring negative voltages. This is achieved through a resistive biasing network that generates the appropriate gate voltages from positive supply rails, making the attenuator compatible with standard positive supply voltage environments while simplifying the bias circuit.

Inventive Principle:

Principle #13The other way round (Inversion)

4Adaptability or versatility

If large DC block capacitors are used for low-frequency operation, then frequency range is extended, but chip area consumption increases significantly

Engineering Contradiction:

Improvelow frequency operationVSAvoidcapacitor area

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent substitutes the mechanical/electrical function of large DC block capacitors with a resistive isolation network. This substitution maintains the ability to block DC while allowing AC signals across a wide frequency range, including low frequencies, without requiring large capacitor structures that consume excessive chip area.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS7839233B2Attenuator

Publication Date: 2010.11.23 ANALOG DEVICES INC

AI summary

A π-type voltage-controlled variable attenuator is disclosed. The variable attenuator may include variably resistive components in the series and shunt arms. The variably resistive components may be implemented as field effect transistors. The shunt arms may be coupled to the series arm, and the variable attenuator may lack capacitors between the series arm and shunt arms. The series arm and shunt arms may display variable resistances which, in combination, operate to provide a variable level of attenuation of an input signal. The variable attenuator may provide any level of attenuation of an input signal over a wide frequency range. The variable attenuator may be implemented as an integrated circuit.