Differential Voltage-Mode Filters With Output Impedance Neutralization

Solution Overview

Problem

Voltage-mode baseband filters for RF signal generators face challenges with nonzero output impedance, leading to poor frequency response and out-of-band rejection, which is unacceptable for applications like quantum computing, where low power consumption and high bandwidth are critical.

Innovation Solution

The implementation of differential voltage-mode filter circuits with neutralization networks that cancel or compensate for the transmission zeros caused by nonzero output impedance, enhancing the frequency response and achieving higher out-of-band rejection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If voltage-mode filter circuits are used to reduce power consumption, then power dissipation is reduced, but output impedance becomes nonzero leading to poor frequency response

Engineering Contradiction:

Improvepower dissipationVSAvoidfrequency response

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

An output buffer stage is introduced as an intermediary between the voltage-mode filter circuit and the load. This buffer has low output impedance to compensate for the nonzero output impedance of the filter circuit, thereby improving the frequency response while maintaining the low power dissipation benefits of the voltage-mode architecture.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The output impedance parameter of the filter circuit is actively compensated by adjusting the output impedance of the buffer stage. By changing the buffer's output impedance parameter to be low, the overall system achieves improved frequency response without increasing the power consumption of the filter circuit itself.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If current-mode circuitry is used to improve frequency response, then out-of-band rejection is improved, but power consumption increases

Engineering Contradiction:

Improveout-of-band rejectionVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

An output buffer stage is introduced as an intermediary between the voltage-mode filter circuit and the load. This buffer has low output impedance to compensate for the nonzero output impedance of the filter circuit, thereby improving the frequency response while maintaining the low power dissipation benefits of the voltage-mode architecture.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The output impedance parameter of the filter circuit is actively compensated by adjusting the output impedance of the buffer stage. By changing the buffer's output impedance parameter to be low, the overall system achieves improved frequency response without increasing the power consumption of the filter circuit itself.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If unity gain buffer is used in voltage-mode filter, then circuit simplicity is maintained, but nonzero output impedance degrades filter response

Engineering Contradiction:

Improvecircuit architectureVSAvoidfilter response

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

An output buffer stage is introduced as an intermediary between the voltage-mode filter circuit and the load. This buffer has low output impedance to compensate for the nonzero output impedance of the filter circuit, thereby improving the frequency response while maintaining the low power dissipation benefits of the voltage-mode architecture.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The unity gain buffer serves a dual function: it provides voltage buffering to maintain circuit simplicity while also serving to compensate for the output impedance effects when properly designed. The buffer essentially serves itself to correct the deficiency of the filter circuit it is connected to.

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS20240413801A1Voltage-mode filters with output impedance neutralization

Publication Date: 2024.12.12 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A device comprises a differential voltage-mode filter circuit comprising first and second voltage-mode filter circuits, and a neutralization network. The first and second voltage-mode filter circuits each comprise a unity gain buffer having a nonzero output impedance. The neutralization network comprises a first neutralization impedance circuit which couples an input of the first voltage-mode filter circuit to an output of the second voltage-mode filter circuit, and a second neutralization impedance circuit which couples an input of the second voltage-mode filter circuit to an output of the first voltage-mode filter circuit. The neutralization network is configured to correct a frequency response of the first and second voltage-mode filter circuits by at least one of cancelling and compensating for at least one transmission zero of a transfer function of each of the first and second voltage-mode filter circuits, which results from the nonzero output impedance of the respective unity gain buffers.