Coupled-Inductor Gain Stage for High-Frequency CMRR
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Solution Overview
Problem
Existing amplifier gain stages suffer from poor Common Mode Rejection Ratio (CMRR) at high frequencies, which degrades receiver sensitivity in high-data-rate communications systems.
Innovation Solution
The introduction of coupled inductances (transformers) within the loading network or between the differential input and output terminals of the gain stage enhances the CMRR, particularly at high frequencies, without degrading the differential transfer function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If standard circuit topologies (resistive load, shunt peaking, inductive interstage network) are used to achieve high bandwidth, then the bandwidth is improved, but the Common Mode Rejection Ratio (CMRR) deteriorates at high frequencies
Solution Approach 1:
A fully differential transconductor is introduced as an intermediary stage between the input differential pair and the output. This transconductor actively compensates for common-mode signals while preserving differential signals, thereby maintaining high CMRR across the entire bandwidth without sacrificing the bandwidth improvements achieved by inductive loading and interstage networks
Solution Approach 2:
The invention changes the operating parameters of the amplifier stages by using fully differential configurations with controlled gain stages. The transconductor parameters are optimized to provide high differential gain while simultaneously rejecting common-mode signals, enabling the system to achieve both high bandwidth and high CMRR
2Reliability
If a tail current generator with high output resistance is used to improve CMRR, then the common mode transconductance is strongly degenerated, but parasitic capacitance at the output node lowers the impedance and rapidly decreases CMRR at high frequencies
Solution Approach 1:
The fully differential transconductor acts as an intermediary that actively maintains high impedance at the output node across all frequencies. By using active feedback and differential signaling, it compensates for the effect of parasitic capacitance, preventing the impedance from dropping at high frequencies and thereby maintaining high CMRR throughout the bandwidth
Solution Approach 2:
The invention ensures continuous high CMRR performance across the entire frequency spectrum by using a fully differential transconductor that actively and continuously compensates for common-mode signals. This continuous action prevents the CMRR from degrading at high frequencies despite the presence of parasitic capacitance
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 approach significantly improves the CMRR at high frequencies, maintaining the differential transfer function while reducing the area occupation, thus enhancing the overall performance of broadband amplifiers for optical communications and RF transceivers.
Implementation Method 1
at least one pair of inductances connected within the loading network or between the differential input transconductor and the differential output terminal, wherein the inductances of at least one pair of inductances are coupled
Data Source
AI summary
The present disclosure relates to a gain stage for an amplifier and to the amplifier. The amplifier may be a broad-band amplifier, trans-impedance amplifier and/or driver amplifier. The gain stage includes a differential input transconductor, a loading network and a differential output terminal. Further, the gain stage includes at least one pair of inductances connected within the loading network or between the differential input transconductor and the differential output terminal.