Transformer-Coupled Input Buffer for Low-Noise Frequency Multiplication
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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 loading of resonant tanks.
Innovation Solution
A frequency synthesis circuit incorporating a transformer-coupled input buffer and injection-locked oscillator, which uses regenerative feedback to enhance injection current with a strong harmonic component, reducing out-of-band phase noise and maintaining high jitter tracking bandwidth without increasing bias current, thereby improving sub-harmonic rejection ratio (SHRR).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If bias current to the injection locked oscillator is increased to enhance injection current, then injection current is enhanced, but resonant tanks are loaded and impedance decreases
Solution Approach 1:
A buffer circuit is introduced as an intermediary between the input signal source and the injection-locked oscillator. This buffer circuit includes a first buffer amplifier with a first resonant tank coupled to its output, and a second buffer amplifier with a second resonant tank coupled to its output. The buffer circuit enhances the injection current delivered to the ILO while the resonant tanks provide impedance matching and isolation, preventing direct loading of the oscillator's resonant tanks. The buffer acts as a mediator that transfers energy efficiently without creating harmful impedance interactions.
Solution Approach 2:
The buffer circuit is divided into two separate buffer amplifiers (first and second), each with its own resonant tank. This segmentation allows independent optimization of each stage and distributes the loading effects across multiple isolated resonant circuits rather than concentrating the burden on a single tank, thereby maintaining higher overall impedance and reducing loading effects on the injection-locked oscillator's resonant tanks.
2Speed
If frequency multiplication is performed at high frequencies, then frequency output is increased, but phase noise and jitter performance deteriorate
Solution Approach 1:
The resonant tanks in the buffer circuit are tuned to resonate at the desired output frequency and its harmonics. This resonant feedback mechanism selectively amplifies the desired frequency components while attenuating noise and jitter. The Q-factor of the resonant tanks provides automatic filtering and noise reduction, improving phase noise and jitter performance even at high frequency multiplication ratios. The resonant circuits create a feedback path that reinforces the fundamental frequency and suppresses spurious signals.
3Productivity
If injection-locked oscillator is used for frequency synthesis, then frequency multiplication is achieved, but locking frequency range is limited
Solution Approach 1:
The buffer circuit employs dynamically可调 (tunable) resonant tanks that can be adjusted to resonate at different frequency multiples of the input signal. This dynamic tuning capability allows the system to adapt to different input frequencies and maintain optimal locking conditions across a broader frequency range. The resonant tanks can be reconfigured to track harmonics at different multiplication ratios, extending the effective locking range of the injection-locked oscillator while maintaining frequency multiplication capability.
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 enables frequency multiplication with reduced out-of-band phase noise and improved jitter tracking bandwidth, while maintaining low impedance loading on resonant tanks, thus enhancing performance in high-frequency applications.
Implementation Method 1
uses regenerative feedback to enhance injection current with a strong harmonic component
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.