Cross-Coupled Oscillator Voltage Sharing for Low-Voltage RF Output
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Solution Overview
Problem
The reduction in transistor supply voltages due to advancements in silicon technology restricts the amplitude of signals in RF circuits, leading to a significant reduction in signal-to-noise ratio (SNR) and spectral purity, which is undesirable in telecommunications applications.
Innovation Solution
An electronic system comprising two cross-coupled oscillators with a shared dynamic ground and a differential amplifier forming a feedback loop to stabilize the supply voltage, allowing for constructive combination of their signals to improve SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the supply voltage is reduced to ensure reliable operation of transistors, then the transistor operates within safe voltage limits, but the peak amplitude of the oscillation signal is limited to just ±500 mV
Solution Approach 1:
The patent divides the oscillation signal generation into two separate oscillators operating in parallel, each handling part of the voltage range. By segmenting the signal path and using two oscillators with complementary phases, the system achieves higher peak-to-peak amplitude (covering the full supply voltage range) while each individual oscillator operates within safe voltage limits, resolving the contradiction between reliability and signal strength.
2Reliability
If the supply voltage is limited to around 700 mV, then the transistor operates reliably, but the signal-to-noise ratio deteriorates significantly
Solution Approach 1:
The patent merges two oscillators with complementary phase relationships to produce a combined output signal. By combining the outputs of both oscillators, the system achieves a higher amplitude signal that improves the signal-to-noise ratio, while each individual oscillator continues to operate at safe voltage levels for reliability. The merging of signalsconstructively adds their amplitudes while maintaining the benefits of lower individual operating voltages.
3Strength
If dual-gate-oxide transistors or lateral-drain-extended transistors are introduced to maintain higher voltages, then the maximum voltage can be maintained at 1.5-1.8 V, but the manufacturing cost increases
Solution Approach 1:
The patent changes the operating parameters of standard transistors by using them in a differential configuration with complementary phases. Instead of requiring special high-voltage transistor structures, the invention achieves effective voltage multiplication through the combination of two oscillators operating at opposite phases, allowing standard transistors to effectively handle higher voltage swings without increasing manufacturing cost.
4Strength
If PMOS transistors are used in a two-differential-pair configuration to share supply voltage, then the oscillation signal amplitude can be increased, but the noise performance deteriorates
Solution Approach 1:
The patent inverts the conventional approach by using NMOS transistors instead of PMOS transistors for the oscillation pairs. Since NMOS transistors have superior noise characteristics compared to PMOS transistors, this inversion maintains high signal amplitude through the two-oscillator configuration while improving rather than deteriorating the noise performance. The complementary phase relationship between the two oscillators is maintained using NMOS devices.
Data Source
AI summary
An electronic system comprises a first and a second oscillator that are mutually cross-coupled and have one and the same resonant frequency, each oscillator comprising an electrical resonator, an active cell having a negative small-signal resistance linked to the electrical resonator, an electric power supply terminal of the active cell, an output for an oscillation signal and a terminal for connection to a ground point, wherein: the electric power supply terminal of the second oscillator and the terminal for connection to a ground point of the first oscillator are linked to one and the same point, termed dynamic ground; and the system also comprises a differential amplifier forming, with the active cell of one of the oscillators, a feedback loop designed to keep the potential of the dynamic ground point at a constant level, dependent on the reference voltage.