RF AC/DC Coupling Circuit Solid-State Relay Parasitic Compensation

Solution Overview

Problem

RF oscilloscopes typically use electromechanical relays due to bandwidth degradation caused by parasitic elements in solid-state relays, which are preferred for their reliability and low power consumption, but these electromechanical relays fail to maintain optimal input return loss across frequency ranges, necessitating expensive active RF switches or complex networks.

Innovation Solution

An RF AC/DC coupling circuit employing a general purpose solid-state relay and carefully chosen inductors to compensate for parasitic elements, developing an inductive input path as frequency increases and partially cancelling parasitic capacitive admittances, thus improving input return loss without requiring expensive or complex methods.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If electromechanical relays are used in RF AC/DC coupling circuits, then bandwidth and input return loss are maintained, but reliability decreases and power consumption increases

Engineering Contradiction:

Improverelay reliabilityVSAvoidparasitic elements degrading bandwidth and frequency response

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful parasitic capacitive effects of solid-state relays into beneficial inductive effects by adding series inductors. These inductors create an inductive input path that counteracts the parasitic capacitance, transforming what was a degradation factor into a bandwidth-extending feature that enables solid-state relays to be used in RF applications.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the electrical parameters of the coupling circuit by introducing carefully chosen inductor values. This parameter modification creates an inductive path that compensates for parasitic capacitance, allowing the circuit to achieve both the reliability of solid-state relays and the bandwidth performance previously only achievable with electromechanical relays.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by stationary object

If solid-state relays are used in RF AC/DC coupling circuits, then reliability and power consumption are improved, but bandwidth and input return loss deteriorate due to parasitic elements

Engineering Contradiction:

Improvepower consumptionVSAvoidparasitic elements

Core Design Contradiction:

Use of energy by stationary objectVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful parasitic capacitive effects of solid-state relays into beneficial inductive effects by adding series inductors. These inductors create an inductive input path that counteracts the parasitic capacitance, transforming what was a degradation factor into a bandwidth-extending feature that enables solid-state relays to be used in RF applications.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Duration of action of stationary object

If solid-state relays are used in RF AC/DC coupling circuits, then reliability is improved, but input return loss and frequency response worsen

Engineering Contradiction:

Improverelay lifespanVSAvoidinput return loss

Core Design Contradiction:

Duration of action of stationary objectVSManufacturing precision

Solution Approach 1:

The patent converts the harmful parasitic capacitive effects of solid-state relays into beneficial inductive effects by adding series inductors. These inductors create an inductive input path that counteracts the parasitic capacitance, transforming what was a degradation factor into a bandwidth-extending feature that enables solid-state relays to be used in RF applications.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent applies preliminary anti-action by introducing inductors that preemptively counteract the parasitic capacitive effects before they can degrade the input return loss and frequency response. This preventive measure allows the circuit to maintain performance specifications while using reliable solid-state relays.

Inventive Principle:

Principle #9Preliminary anti-action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration enhances the bandwidth of RF AC/DC signal coupling, eliminating the need for costly or complex solutions by effectively managing parasitic elements associated with solid-state relays and neighboring circuitry, maintaining optimal input return loss across frequencies.

Implementation Method 1

The first inductor and the second inductor may be configured to develop an inductive input path as a frequency of an input signal increases to overcome parasitic elements associated with the general purpose solid-state relay

Methodology Applied

Scientific EffectInductive reactance: Inductor

Implementation Method 2

The first inductor and the second inductor may be configured to partially cancel parasitic capacitive input admittances of the general purpose solid-state relay, the measuring device, and the first capacitor

Methodology Applied

Scientific EffectParasitic capacitance compensation: Parasitic Capacitance

Data Source

PatentUS8129867B2RF AC/DC coupling circuit using general purpose solid-state relay

Publication Date: 2012.03.06 NATIONAL INSTRUMENTS CORP

AI summary

A system and method for overcoming the parasitic elements associated with off the shelf or general purpose solid-state devices configured to operate as RF AC/DC signal coupling networks. An AC/DC signal coupling network may comprise a general purpose solid-state relay device and two inductors having values carefully chosen to compensate for the imperfections and intrinsic parasitic elements associated with the solid-state relay. The inductors may also have values carefully chosen to compensate for the parasitic elements of the neighboring or coupled circuit, and for the capacitance that is associated with the printed circuit board bond pad that is directly dependent upon the area of the pad and distance to the neighboring conductors. The inductors may cause the input path to become inductive as the signal frequency increases, and also improve the input return loss over the RF input range.