Complementary LO Buffer for Common-Mode Noise Rejection
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Solution Overview
Problem
High-performance radio transceivers face challenges in maintaining signal balance and rejecting common-mode noise in local oscillator (LO) buffers, leading to phase errors and unwanted spurs, particularly due to lengthy distribution lines and interference.
Innovation Solution
A local oscillator buffer circuit utilizing a complementary common-source and source-follower stage configuration with matched transconductances, implemented using CMOS technology, to enhance common-mode rejection and phase error correction, thereby reducing power consumption and integrating well with low power supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional LO buffer is used, then the LO signal is amplified, but common-mode noise and interference are not rejected, leading to phase errors and spurs
Solution Approach 1:
The LO buffer is divided into two separate complementary stages: a common-source stage for signal amplification and a source-follower stage for common-mode rejection. This segmentation allows each stage to perform its specific function optimally, with the common-source stage providing gain and the source-follower stage rejecting common-mode noise and interference.
Solution Approach 2:
The source-follower stage acts as an intermediary between the common-source amplification stage and the subsequent frequency divider. It mediates by buffering the amplified signal while simultaneously rejecting common-mode noise, thereby protecting the downstream circuitry from phase errors and spurs caused by power supply interference.
2Measurement precision
If differential circuitry is used for LO generation, then phase errors are reduced, but coupling of power supply disturbances remains
Solution Approach 1:
The source-follower stage extracts and rejects common-mode components from the differential signal. By taking out the common-mode noise and interference that couples through the power supply, it allows the differential circuitry to maintain its phase accuracy while being protected from power supply disturbances.
3Use of energy by moving object
If CMOS technology is used, then power consumption is reduced, but common-mode rejection capability may be limited
Solution Approach 1:
The buffer employs a composite architecture combining two different CMOS transistor configurations (common-source and source-follower) with complementary p-channel and n-channel transistors. This composite structure achieves high common-mode rejection ratio (CMRR) while maintaining low power consumption suitable for modern CMOS fabrication processes.
Data Source
AI summary
A local oscillator buffer circuit comprises a complementary common-source stage comprising a first p-channel transistor (MCSP) and a first n-channel transistor (MCSN), arranged such that their respective gate terminals are connected together at a first input node, and their respective drain terminals of each of is connected together at a buffer output node. A complementary source-follower stage comprises a second p-channel transistor (MSFP) and a second n-channel transistor (MSFN), arranged such that their respective gate terminals are connected together at a second input node, and their respective source terminals are connected together at the buffer output node.