Transformer-Coupled Input Buffer for Low-Noise Frequency Synthesis
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Solution Overview
Problem
Existing frequency synthesis circuits, particularly phase-locked loops (PLLs) and open loop doublers, face challenges in achieving suitable phase noise and jitter performance at high frequencies, along with high power consumption and noise degradation, while injection-locked oscillators suffer from a narrow locking frequency range and impedance issues when bias current is increased.
Innovation Solution
A frequency synthesis circuit incorporating a transformer-coupled input buffer with regenerative feedback enhances injection current with a strong harmonic component to an injection-locked oscillator, avoiding increased bias current and reducing out-of-band phase noise, thereby improving jitter tracking bandwidth and sub-harmonic rejection ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If bias current is increased to expand locking frequency range in injection-locked oscillators, then locking frequency range is improved, but impedance increases causing degraded phase noise performance
Solution Approach 1:
A buffer stage is introduced as an intermediary between the input signal source and the injection-locked oscillator. This buffer amplifies the injection signal without requiring increased bias current in the ILO, thereby expanding the effective locking range while maintaining proper impedance levels and avoiding phase noise degradation.
Solution Approach 2:
The frequency synthesis system is segmented into distinct functional blocks: an input buffer stage and an injection-locked oscillator stage. This segmentation allows independent optimization of each stage - the buffer handles signal amplification and impedance matching, while the ILO maintains low impedance for low phase noise.
2Power
If bias current is increased to improve injection signal strength, then injection current is improved, but resonant tanks become loaded degrading oscillator performance
Solution Approach 1:
The buffer acts as an intermediary that provides the necessary current amplification for strong injection signals without requiring the oscillator's bias current to be increased. This protects the resonant tanks from excessive loading while still delivering strong injection current to the ILO.
3Stability of the object's composition
If phase-locked loops are used for frequency synthesis, then frequency stability is improved, but power consumption increases and noise degradation occurs at high frequencies
Solution Approach 1:
The invention extracts and eliminates the high-power PLL subsystem from the frequency synthesis architecture, replacing it with a low-power injection-locked oscillator-based system. The ILO achieves frequency stability through its natural locking mechanism without requiring the power-intensive phase detector, charge pump, and loop filter of a PLL.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides reduced out-of-band phase noise and improved jitter tracking bandwidth with high frequency multiplication, maintaining low impedance in resonant tanks and achieving good sub-harmonic rejection ratio without increasing bias current.
Implementation Method 1
regenerative feedback in a transformer-coupled input buffer to enhance injection current with a strong harmonic component to an injection-locked oscillator
Implementation Method 2
transformer-coupled input buffer
Implementation Method 3
A first resonant tank of an inductor in parallel with a capacitor is coupled between a power supply terminal and the first transistor. A second resonant tank of an inductor in parallel with a capacitor is coupled between the power supply terminal and the second transistor. The first and second resonant tanks are tuned to a selected harmonic of the input frequency.
Data Source
AI summary
A frequency synthesis circuit includes a first inductor coupled to receive a first input signal at an input frequency, and a second inductor coupled to receive second input signal at the input frequency and out-of-phase relative to the first input signal. The circuit has first and second transistors with control terminals coupled to the first and second inductors, respectively. A first resonant tank of an inductor in parallel with a capacitor is coupled between a power supply terminal and the first transistor. A second resonant tank of an inductor in parallel with a capacitor is coupled between the power supply terminal and the second transistor. The first and second resonant tanks are tuned to a selected harmonic of the input frequency. An injection-locked oscillator has inputs coupled to the first and second transistors.