Digital RF Attenuator Circuit for On-Chip AGC Without Distortion

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Solution Overview

Problem

Existing RF tuners face challenges in performing Automatic Gain Control (AGC) without causing distortion, especially when attenuation is needed before distortion-causing circuitry like amplifiers, and pin-diode attenuators cannot be integrated on semiconductor chips for tuner-on-chip applications.

Innovation Solution

A digitally-controllable attenuator circuit using a voltage-divider arrangement with two adjustable impedance components, where each component has selectable discrete elements that can be switched on or off using digital control lines, allowing for precise impedance adjustments and attenuation control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If pin-diode attenuator is used in the signal path, then attenuation can be performed before distortion-causing circuitry, but the attenuator cannot be built on a semiconductor chip

Engineering Contradiction:

Improveintegrate abilityVSAvoidattenuation function

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The attenuator is divided into multiple discrete impedance elements that can be individually selected and combined. This segmentation allows the attenuator to be implemented using standard semiconductor components that can be integrated on-chip, while still providing the required attenuation functionality through selective combination of impedance elements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the physical implementation parameters of the attenuator from pin-diode based (off-chip) to discrete impedance elements (on-chip). By varying the impedance values and configurations of these discrete elements, the attenuator achieves the required attenuation characteristics while being suitable for semiconductor integration.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If analog AGC is performed inside the first amplifier, then gain control is achieved, but distortion occurs

Engineering Contradiction:

Improvegain controlVSAvoiddistortion

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The attenuator is placed before the first amplifier in the signal path to perform preliminary signal level reduction. By attenuating large input signals before they enter the amplifier, the amplifier operates within its linear region and avoids distortion, while still allowing analog AGC to function properly inside the amplifier for fine gain control.

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If attenuation is performed on large input signals, then signal levels are maintained within desired range, but noise and distortion may increase

Engineering Contradiction:

Improvesignal level controlVSAvoidnoise

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The discrete impedance elements act as an intermediary between the input signal and the amplifier. By providing a controlled attenuation path through these passive impedance elements, the signal level is reduced to an appropriate range for the amplifier without introducing active noise sources, thus maintaining signal integrity while preventing amplifier overload.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS7477085B2Digital attenuator circuits and methods for use thereof

Publication Date: 2009.01.13 QUALCOMM INC

AI summary

An attenuator system includes a first adjustable impedance component on a first current path between a input component and a output component, and a second adjustable impedance component between the first current path and ground, wherein each of the first and second adjustable impedance components include a plurality of selectable, discrete legs, each leg having an impedance.