Transformer-Coupled Frequency Doubler for Low Phase Noise
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Solution Overview
Problem
Conventional oscillators and phase-locked loops (PLLs) face challenges in achieving low phase noise at high frequencies, such as 28 GHz, which is essential for high-speed data transmission like 224 Gbps PAM-4 transmitters, due to limitations in capacitor quality factor and increased power consumption in N-coupled oscillator designs.
Innovation Solution
The implementation of a frequency doubler or tripler architecture that employs current re-use coupled oscillator techniques, where two oscillators operate at different frequencies, with coupling via a transformer, enhancing phase noise performance without increasing current consumption by utilizing a virtual ground node and frequency tracking loop to improve capacitor quality factor and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional oscillators and PLLs are used at 28 GHz, then high frequency clock generation is achieved, but phase noise exceeds the -103 dBc/Hz specification at 1 MHz offset
Solution Approach 1:
The oscillator is divided into two coupled oscillators operating at different frequencies (f1 and f2 = 2*f1). The first oscillator runs at a lower frequency where capacitor quality factor is higher, achieving better phase noise performance. The second oscillator generates the required high frequency through harmonic relationship, eliminating the need for high-frequency capacitors with poor quality factors.
Solution Approach 2:
The invention changes the operating frequency parameter of the oscillators. Instead of using a single oscillator at the target high frequency (28 GHz), it uses two oscillators at lower frequencies (e.g., 14 GHz and 28 GHz) where the capacitors can achieve higher quality factors, thereby improving phase noise performance while maintaining the required output frequency.
2Measurement precision
If N-coupled oscillator designs are used to improve phase noise, then phase noise performance is enhanced, but power consumption increases
Solution Approach 1:
Two oscillators are coupled together through mutual inductance to share the power consumption burden. The coupled oscillators operate at different frequencies with a harmonic relationship, allowing them to leverage the higher quality factor of capacitors at lower frequencies while generating the required high-frequency output, achieving better phase noise without proportional power increase.
Solution Approach 2:
A coupling mechanism (mutual inductance between oscillators) serves as an intermediary to transfer energy and synchronize operation. This coupling allows the oscillators to work together efficiently, improving phase noise performance through cooperative operation rather than requiring each oscillator to independently achieve the target performance with higher power consumption.
3Measurement precision
If capacitor quality factor is increased to reduce phase noise, then phase noise performance improves, but device complexity and current consumption increase
Solution Approach 1:
Instead of trying to achieve high phase noise performance at the high operating frequency by using high-quality-factor capacitors at high frequencies (which is difficult and complex), the invention inverts the approach: it uses lower-frequency oscillators where capacitors naturally have higher quality factors, then generates the high-frequency output through the harmonic relationship between the coupled oscillators.
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
This approach achieves up to 4.5 dB better phase noise performance, enabling high-speed serial data transmission rates of 224 Gbps and beyond by improving the quality factor of capacitors and reducing power consumption, thus meeting stringent jitter and phase noise requirements.
Implementation Method 1
a transformer coupled to the first oscillator; and a second oscillator coupled to the transformer
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A frequency doubler (tripler, or quadrupler) employs current re-use coupled oscillator technique to enhance phase noise without increasing current consumption. Frequency doubler uses coupling between two oscillators running at different frequencies; a first oscillator is running at the target frequency and a second oscillator is running at half the frequency. The coupling between the two oscillators is via a transformer having a primary transformer coil and a secondary transformer coil. The first oscillator comprises a differential inductor, coarse/fine tuning capacitor arrays, and an n-type trans-conductor (GM). A virtual ground node of the n-type GM is coupled to one side of the primary transformer coil and the other side of the primary coil is coupled to the center tap of the secondary coil. The second oscillator comprises the secondary coil, coarse/fme tuning capacitor arrays, n-type GM, frequency tracking loop (FTL) and 2nd-harmonic LC filter network.