RF Equalizer Topology for Flat Gain in ET Circuits
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Solution Overview
Problem
Conventional RF equalizers in envelope tracking circuits for 5G-NR communication devices face challenges in maintaining flat amplitude response and constant negative group delay across high frequency ranges, particularly around 100 MHz, leading to non-linear responses and compromised performance.
Innovation Solution
A two-operational amplifier (op-amp) structure with a specific feedback impedance network and differential input nodes is used to provide a flat gain and constant negative group delay across a frequency range of interest, incorporating both real and complex zeros in the transfer function to achieve flat amplitude and group delay responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RF equalizers are used in envelope tracking circuits, then the circuit can operate at high frequencies, but the amplitude response becomes non-linear and group delay becomes non-constant around 100 MHz
Solution Approach 1:
The equalizer is divided into two separate operational amplifier stages: a first op-amp providing voltage gain and a second op-amp providing additional gain and impedance transformation. This segmentation allows each stage to be optimized for specific functions, achieving flat amplitude response and constant group delay through coordinated design of the two stages rather than requiring a single complex equalizer structure.
Solution Approach 2:
The patent employs specific impedance values in the feedback networks of both op-amps (R1, R2, R3, R4, C1, C2) that are carefully selected to achieve the desired frequency response characteristics. By changing and optimizing these circuit parameters, the equalizer achieves flat amplitude response and constant negative group delay across the frequency range up to 200 MHz without requiring overly complex architecture.
2Speed
If the frequency range is extended to 200 MHz for 5G-NR communication, then higher data rates are achieved, but maintaining flat gain and constant group delay becomes increasingly difficult
Solution Approach 1:
Both operational amplifiers incorporate feedback networks with resistors and capacitors (R1-C1 for the first op-amp, R2-C2 for the second op-amp) that provide frequency-dependent feedback. This feedback mechanism allows the equalizer to actively compensate for frequency response variations and maintain precise control over gain and group delay characteristics across the extended frequency range up to 200 MHz.
Solution Approach 2:
The equalizer design allows the circuit characteristics to dynamically adapt across the frequency spectrum through the frequency-dependent behavior of the RC feedback networks. The impedance of the capacitive elements changes with frequency, enabling the equalizer to automatically adjust its response to maintain flat gain and constant group delay across the wide frequency range required for 5G-NR communication.
3Device complexity
If a simple equalizer structure is used, then device complexity is reduced, but the ability to provide flat amplitude response and constant group delay across high frequencies is compromised
Solution Approach 1:
The patent combines multiple functions into a unified two-op-amp structure that simultaneously provides voltage gain, impedance matching, and frequency response equalization. The first op-amp handles the primary amplification while the second op-amp provides additional gain and impedance transformation, merging these functions into a compact architecture that achieves precise frequency response control without requiring separate circuits for each function.
Data Source
AI summary
A radio frequency (RF) equalizer in an envelope tracking (ET) circuit is disclosed. A transmitter chain includes an ET circuit having an RF equalizer therein. The RF equalizer includes a two operational amplifier (op-amp) structure that provides a relatively flat gain and a relatively constant negative group delay across a frequency range of interest (e.g., up to 200 MHz). The simple two op-amp structure provides frequency response equalization and time tuning adjustment and/or creates a window Vcc signal.