Distributed Amplifier Band-Pass Tuning via Unmatched Termination

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Solution Overview

Problem

Conventional distributed amplifiers have a limited low frequency range of operation due to the cut-off frequency of the transmission line associated with the amplifier, which restricts their bandwidth and gain performance.

Innovation Solution

A broadband and band-pass distributed amplifier design is achieved by not matching the termination impedance with the characteristic impedance of the transmission lines, using short circuits for signal termination, and absorbing parasitic capacitors to create an artificial transmission line with higher cut-off frequency, allowing for controllable bandwidth and improved gain and noise performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional distributed amplifiers use matched termination impedance with characteristic impedance of transmission lines, then signal stability is improved, but bandwidth is limited due to cut-off frequency

Engineering Contradiction:

Improvesignal stabilityVSAvoidbandwidth

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent changes the termination impedance parameter from matched (equal to characteristic impedance) to unmatched (different from characteristic impedance). This parameter change transforms the low-pass frequency response into a band-pass response, enabling the amplifier to operate at higher frequencies beyond the traditional cut-off frequency while maintaining signal stability through controlled reflections.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If transmission line cut-off frequency is used to limit bandwidth, then low frequency operation is stable, but high frequency range is restricted

Engineering Contradiction:

Improvelow frequency stabilityVSAvoidfrequency range

Core Design Contradiction:

Stability of the object's compositionVSSpeed

Solution Approach 1:

The patent introduces dynamic behavior to the termination impedance, making it frequency-dependent rather than static. By using unmatched termination, the system dynamically reflects signals at different frequencies, allowing low frequency signals to be stabilized while high frequency signals are constructively reflected back, thereby expanding the operational frequency range.

Inventive Principle:

Principle #15Dynamics

3Ease of operation

If matched termination is used in distributed amplifier, then impedance matching is achieved, but gain bandwidth product is limited

Engineering Contradiction:

Improveimpedance matchingVSAvoidgain bandwidth product

Core Design Contradiction:

Ease of operationVSProductivity

Solution Approach 1:

Instead of using matched termination to achieve impedance matching, the patent inverts the approach by using unmatched termination. This inversion creates controlled reflections that add constructively to the forward traveling wave, thereby increasing the gain bandwidth product while maintaining ease of operation through simplified termination design.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS8686790B2Distributed amplifier for band pass radio front-end

Publication Date: 2014.04.01 MALIKIE INNOVATIONS LTD

AI summary

A distributed amplifier is provided that is broadband and band pass with controllable bandwidth. In the distributed amplifier circuit, termination impedance of the input transmission line is not matched with the characteristics impedance of the input transmission line and/or the termination impedance of the output transmission line is not matched with the characteristics impedance of the output transmission line, thus providing the broadband and band pass with controllable bandwidth attributes.