AC-Coupled Local Oscillator Divider for Stable I/Q Locking
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Solution Overview
Problem
Frequency dividers in wireless communication systems face challenges due to strong temperature and process variations, affecting their frequency range and functionality, particularly in tail transistors, which can lead to unstable locking characteristics and phase shifts between input local oscillator signals and output frequency divider signals.
Innovation Solution
The implementation of AC coupling between tail transistors and input buffers, along with a reference current source, such as a current mirror, to stabilize the quiescent current and allow independent biasing of tail transistors, reducing phase shift and enhancing frequency divider stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct coupling between tail transistors and input buffers is used, then device complexity is reduced, but temperature and process variations cause unstable locking characteristics and phase shifts
Solution Approach 1:
AC coupling capacitors are introduced as intermediary components between the tail transistors and input buffers. These capacitors block DC variations caused by temperature and process changes while allowing AC signal transmission, thereby stabilizing the locking characteristics without significantly increasing circuit complexity
Solution Approach 2:
The coupling method is changed from direct DC coupling to AC coupling by introducing capacitors. This parameter change in the coupling structure isolates the tail transistors from DC variations, maintaining stable locking characteristics across temperature and process variations
2Reliability
If AC coupling capacitors are added between tail transistors and input buffers, then locking characteristics are stabilized, but device complexity increases
Solution Approach 1:
AC coupling capacitors serve as intermediary elements that provide isolation between stages. They are simple passive components that effectively block DC variations while maintaining signal integrity, achieving reliability improvement with minimal complexity increase
3Reliability
If independent bias voltage sources are used for tail transistors, then phase shift is reduced and stability is improved, but device complexity and power consumption increase
Solution Approach 1:
The biasing system is segmented into independent bias voltage sources for each tail transistor. This segmentation allows individual optimization and control of each transistor's operating point, reducing phase shifts and improving stability without requiring complete redesign of the bias network
Solution Approach 2:
Independent regulatable bias voltage sources are implemented to separately control the operating parameters of each tail transistor. This parameter control enables precise adjustment to minimize phase shifts while maintaining stability, with the complexity managed through systematic design
Data Source
AI summary
Aspects of the disclosure relate to a local oscillator frequency divider for a receiver or transmitter. In this regard a frequency divider has a first frequency input coupled to a first oscillator frequency output, a second frequency input coupled to a complementary second oscillator frequency output, a first in-phase/quadrature (I/Q) divided frequency output, and a complementary second I/Q divided frequency output. The frequency divider further has a first alternating current (AC) coupling capacitor between the first frequency input and the first oscillator frequency output and a second AC coupling capacitor between the second frequency input and the second oscillator frequency output.