Gilbert Mixer Negative-gm Feedback for Low-Swing Saturation
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Solution Overview
Problem
Conventional Gilbert mixers in 60 GHz wireless systems require a higher input signal swing voltage to prevent saturation, leading to reduced power efficiency and linearity in the baseband signal path.
Innovation Solution
The implementation of cross-coupled negative gm feedback technique using NMOS transistors reduces the input signal swing voltage required for saturation, allowing the Gilbert mixer to operate in current mode at 150 mV, thereby improving power efficiency and linearity by increasing the gain of the transmit chain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Gilbert mixer is used with higher input signal swing voltage to prevent saturation, then the mixer can operate reliably, but power efficiency and linearity in the baseband signal path deteriorate
Solution Approach 1:
The patent implements a negative gm feedback mechanism using cross-coupled NMOS transistors (M16-M19) that sense the drain current and apply a feedback voltage to the gates of the input transistors (M12-M15). This feedback loop dynamically adjusts the transistor operating point to maintain saturation at reduced input signal swing voltages (150 mV), thereby improving power efficiency while ensuring reliable mixer operation without requiring higher voltage swings that would consume more power.
2Reliability
If conventional Gilbert mixer is used with higher input signal swing voltage to prevent saturation, then the mixer can operate reliably, but linearity in the baseband signal path deteriorates
Solution Approach 1:
The negative gm feedback mechanism using cross-coupled NMOS transistors (M16-M19) continuously monitors and adjusts the operating point of the input transistors (M12-M15) to maintain optimal linearity. By applying feedback control, the system keeps the transistors in the saturation region even at reduced voltage swings (150 mV), thereby preserving baseband signal linearity while ensuring reliable mixer operation without requiring higher voltage swings that would degrade linearity.
3Use of energy by moving object
If input signal swing voltage is reduced to 150 mV for current mode operation, then power efficiency improves, but saturation control becomes more difficult
Solution Approach 1:
The patent employs a negative gm feedback circuit using cross-coupled NMOS transistors (M16-M19) that automatically adjusts the gate voltages of input transistors (M12-M15) based on their drain current. This feedback mechanism dynamically maintains the transistors in saturation mode at reduced voltage swings (150 mV), thereby achieving improved power efficiency while managing saturation control complexity through automated feedback rather than manual biasing or more complex circuit topologies.
Data Source
AI summary
A cross coupled NMOS transistors providing a negative gm transistor feedback allows a mixer to saturate at a reduced input signal swing voltage when compared to a conventional mixer allowing the mixer to enter into the current mode operation at a reduced signal input voltage range. The linearity of the baseband signal path can be traded against the mixer gain and is improved if the signal swing in the baseband signal path is reduced. The input mixer transistors operate in the saturated mode at a reduced input signal swing voltage causing the power efficiency of the system to increase since the transmit chain operates at a class-D power efficient. Efficiency is very important in mobile applications to save and extend the battery power of a mobile phone providing a better utilization of the available power since most of that power is supplied to the energy of the outgoing modulated signal.