RF Mixer CGCS Transconductance Stage for Low-Q Matching

Solution Overview

Problem

Conventional common-gate only (CGO) input stages in wireless device receivers require high Q matching networks for high gain, making them sensitive to input Q matching factor and costly to implement.

Innovation Solution

The introduction of a common-gate common-source (CGCS) input stage, which includes a pair of NMOS transistors and a pair of PMOS transistors with a current source, decouples transconductance gain from the high Q matching network by adding a common-source stage through the PMOS differential-pair.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a conventional common-gate only (CGO) input stage is used, then the circuit structure is simple, but high gain requires a very high Q matching network which increases sensitivity and cost

Engineering Contradiction:

Improvecircuit structureVSAvoidsensitivity to input Q matching factor

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The input stage is segmented into two functional blocks: a common-gate stage (first pair of transistors) and a common-source stage (second pair of transistors). This segmentation allows each stage to contribute differently to the overall transconductance, with the common-source stage providing additional gain without requiring high Q matching networks, thereby reducing sensitivity while maintaining circuit functionality.

Inventive Principle:

Principle #1Segmentation

2Ease of manufacture

If a conventional common-gate only (CGO) input stage is used, then the circuit is easier to implement, but achieving high gain requires very high Q matching networks which increases cost

Engineering Contradiction:

Improveimplementation easeVSAvoidmatching network requirements

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The input stage is segmented into two functional blocks: a common-gate stage (first pair of transistors) and a common-source stage (second pair of transistors). This segmentation allows each stage to contribute differently to the overall transconductance, with the common-source stage providing additional gain without requiring high Q matching networks, thereby reducing sensitivity while maintaining circuit functionality.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS8401510B2Common-gate common-source transconductance stage for RF downconversion mixer

Publication Date: 2013.03.19 QUALCOMM INC

AI summary

In an embodiment, a method and apparatus for downconverting a received RF signal in a wireless device where differential signals from an off-chip matching network may be input to a CGCS input stage of a mixer, which downconverts the signals to baseband or some intermediate frequency. The input stage includes a pair of NMOS transistors in a common-gate configuration and a pair of PMOS transistors in a common-source configuration. A potential advantage of the CGCS input stage over the existing CGO transconductance stage configuration is that by adding a common-source stage through the PMOS differential-pair, the transconductance gain is decoupled from the high Q matching network.