Transconductance LNA with gm-Enhanced Buffer for RF Front-End Linearity
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Solution Overview
Problem
RF receiver front-ends face challenges in achieving high-gain, high-linearity, low-noise, and low-power performance due to the additional transconductance amplifier's gain coming at the cost of reduced linearity and increased power consumption, and the use of an RSSI module leading to increased cost and degraded noise figure.
Innovation Solution
The proposed RF receiver front-end architecture includes a transconductance LNA, a current-driven passive mixer, and gm-enhanced CG buffers, which eliminate the need for an additional transconductance amplifier, reduce noise, and improve linearity by operating in the current domain and using AC coupling, thereby achieving higher-gain, higher-linearity, and lower-noise with lower power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an additional transconductance amplifier is used to provide higher gain, then gain is improved, but linearity deteriorates and power consumption increases
Solution Approach 1:
The patent merges the functions of the LNA and transconductance amplifier into a single integrated circuit. The LNA is designed with current-mode operation and includes an output current source that directly drives the mixer, eliminating the need for a separate transconductance amplifier stage while maintaining both gain and linearity performance.
Solution Approach 2:
The patent changes the operating mode from voltage-mode to current-mode amplification. By designing the LNA to output current signals that directly drive the mixer, the system achieves high gain without the linearity degradation associated with voltage-mode operation and additional amplification stages.
2Power
If an additional transconductance amplifier is used to provide higher gain, then gain is improved, but power consumption increases
Solution Approach 1:
The patent combines multiple functions (LNA, transconductance amplification, and driver stage) into a single integrated circuit, eliminating the need for separate additional amplifiers that would increase power consumption while maintaining the required gain.
Solution Approach 2:
The LNA is designed with an integrated output current source that directly drives the mixer without requiring external additional amplification stages. The circuit uses AC coupling to block DC current while allowing RF signals to pass, reducing power consumption while maintaining performance.
3Reliability
If an RSSI module is used to improve linearity, then linearity is improved, but cost increases and noise figure deteriorates
Solution Approach 1:
The patent integrates the linearity improvement function directly into the LNA circuit design itself, rather than using a separate RSSI module. The current-mode LNA with integrated output current source provides inherent linearity without requiring external measurement and control modules.
Solution Approach 2:
The patent extracts the linearity control function from a separate RSSI module and incorporates it directly into the LNA circuit topology. By designing the LNA to operate in current-mode with direct current driving of the mixer, linearity is achieved intrinsically without additional cost and complexity.
Data Source
AI summary
Embodiments of an RF receiver front-end are presented herein. In an embodiment, the RF receiver front-end comprises a transconductance LNA, a passive mixer, and a gm-enhanced common-gate buffer. The transconductance LNA is configured to convert an RF voltage signal to an RF current signal and provide the RF current signal at an output. The passive mixer is coupled to the output of the transconductance LNA and is configured to mix the RF current signal with a local oscillator signal to produce a frequency translated current signal. The gm-enhanced common-gate buffer is configured to receive the frequency translated current signal at an input and convert the frequency translated current signal to a frequency translated voltage signal. In an embodiment, the input of the gm-enhanced common-gate buffer is configured to provide a low input impedance to limit a voltage swing of the frequency translated current signal.