Common-Mode Suppression Resonator for Amplifier Signal Integrity
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Solution Overview
Problem
Semiconductor amplifiers struggle with common mode (CM) signal interference, which distorts output signals and causes instability due to non-ideal CM rejection, especially from radio frequency noise and electromagnetic interference (EMI).
Innovation Solution
A circuit and method employing a common mode suppression (CMS) block with conductive traces and a defected ground plane, forming a resonator structure that suppresses CM signals without affecting differential mode (DM) signals, using a monolithic substrate to integrate CMS and amplifier components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional amplifier is used, then the amplifier can amplify differential mode signals, but common mode signals are amplified along with the differential mode signals causing output distortion
Solution Approach 1:
The invention divides the ground plane into separate regions: a first ground region connected to the negative terminal of the differential mode signal and a second ground region connected to the common mode signal. This segmentation allows the amplifier to process differential mode signals while rejecting common mode signals, as each ground region provides a separate reference path that prevents common mode interference from coupling into the differential signal path.
2Reliability
If an ideal amplifier with infinite CM rejection is used, then common mode gain would be zero, but real amplifiers have non-ideal CM rejection and must address CM realities
Solution Approach 1:
The invention introduces an intermediary element - the defected ground plane structure with its specific inductance and capacitance values - that mediates between the common mode signal and the amplifier input. This intermediary structure provides a controlled impedance path that transforms the common mode signal into a form that the amplifier can reject, effectively creating a passive pre-processing stage that reduces the burden on the active amplifier circuitry.
3Stability of the object's composition
If the amplifier operates under CM excitation, then the output signal becomes unstable and exhibits oscillations
Solution Approach 1:
The invention performs preliminary action by pre-filtering common mode signals through the defected ground plane structure before they reach the amplifier. The specific inductance (0.5 nH) and capacitance (0.2 pF) values are designed to create a notch filter that attenuates common mode signals in the frequency range where oscillations would occur, preventing the amplifier from entering unstable operating conditions in the first place.
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
The CMS block effectively reduces CM interference by 20-25 dB across a wide band of frequencies, maintaining signal integrity and stability by minimizing CM gain while preserving DM signal quality.
Implementation Method 1
A circuit and method employing a common mode suppression (CMS) block with conductive traces and a defected ground plane, forming a resonator structure that suppresses CM signals
Data Source
AI summary
A semiconductor device has an amplifier and common mode suppression (CMS) circuit formed on a common substrate. The CMS circuit has a first input and second input coupled for receiving an input signal and further has a first output coupled to a first input of the amplifier and a second output coupled to a second input of the amplifier to reduce common mode. The CMS circuit further has a ground plane, a first conductive trace disposed over the ground plane and coupled between the first input and first output, second conductive trace disposed over the ground plane and coupled between the second input and second output, and third conductive trace disposed over the ground plane with a first end of the third conductive trace coupled to the ground plane and a second end of the third conductive trace open circuit to form a resonator.