Transformer Tail Filter for Complementary Oscillator Phase Noise
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Solution Overview
Problem
Designing satisfactory local oscillator circuitry for electronic devices with wireless communications capabilities is challenging due to the sensitivity of phase noise in the oscillator path, which affects signal-to-noise and distortion ratio, particularly with stringent error vector magnitude requirements in modern modulation schemes.
Innovation Solution
Implementing a transformer-based tail filter in the oscillator circuitry that couples n-type and p-type transistors through 1:1 impedance transformers, decoupling the tunable capacitor from the decoupling network inductance, thereby reducing the resonance dependence on decoupling network components and directing second harmonic power through the transformer-based resonant tank.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional decoupling network is used in the oscillator circuitry, then the circuit structure is simple, but the resonance depends heavily on decoupling network inductance which degrades phase noise performance
Solution Approach 1:
The patent introduces a transformer-based tail filter as an intermediary component between the n-type and p-type cross-coupled transistor pairs. This transformer filter acts as a mediator that decouples the resonance from the decoupling network inductance, allowing the resonance to be determined by the tail filter components (inductors Ls1/Ls2 and capacitor Cs) rather than the decoupling network. This intermediary structure improves phase noise suppression by isolating the critical resonance path from harmful inductance while maintaining circuit functionality.
2Adaptability or versatility
If the tunable capacitor is directly connected to the decoupling network, then the capacitance can be easily tuned, but the resonance becomes dependent on decoupling network inductance affecting phase noise
Solution Approach 1:
The transformer-based tail filter serves as an intermediary that connects the tunable capacitor to the rest of the circuit while isolating it from the decoupling network inductance. The capacitor Cs is connected to the secondary side of the transformers, allowing capacitance tuning for frequency adjustment while the transformer coupling ensures that the resonance is determined by the tail filter components rather than the decoupling network. This resolves the contradiction by maintaining tuning capability while eliminating phase noise degradation.
Solution Approach 2:
The patent segments the oscillator circuit into distinct functional blocks: the cross-coupled transistor pairs for signal generation, the transformer-based tail filter for resonance control, and the decoupling network for power supply stabilization. By segmenting the circuit, the resonance function is separated from the decoupling network, allowing independent optimization of each block. The tunable capacitor is part of the tail filter segment rather than the decoupling network segment, enabling capacitance tuning without introducing decoupling network inductance into the resonance path.
3Reliability
If larger tail inductors are used to improve phase noise, then phase noise suppression is enhanced, but the circuit area increases
Solution Approach 1:
The patent changes the parameters of the tail filter by using the transformers to refer the tunable capacitor Cs exactly between the plus and minus terminals of the tail inductors Ls1 and Ls2. This parameter transformation allows the resonance to be determined by the tail filter components rather than being dependent on large decoupling network inductors. The transformer coupling enables the use of smaller inductors while maintaining or improving phase noise performance, thus reducing the required circuit area.
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 configuration enhances phase noise suppression and allows for optimized tail resonator sizing, improving the overall performance of wireless communications by reducing phase noise and enhancing signal quality.
Implementation Method 1
a first filter coil inductively coupled to the first tail coil, a second filter coil inductively coupled to the second tail coil
Implementation Method 2
The first tail coil and the first filter coil can be vertically stacked with respect to each other in an interconnect stack. The second tail coil and the second filter coil can be vertically stacked with respect to each other in the interconnect stack.
Data Source
AI summary
An electronic device may include wireless circuitry having an oscillator. The oscillator can include a pair of n-type transistors coupled to a first tail node, a pair of p-type transistors coupled to a second tail node, a load inductor coupled between the pair of n-type transistors and the pair of p-type transistors, a load capacitor coupled between the pair of n-type transistors and the pair of p-type transistors, a tunable capacitor, and a first transformer coupled between the first tail node and the tunable capacitor. The oscillator can further include a second transformer coupled between the second tail node and the tunable capacitor. The tunable capacitor can include multiple differential switchable capacitor circuits.