Oscillator Capacitor Switching With Over-Drive for Low Phase Noise
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Solution Overview
Problem
Oscillation circuits face limitations in quality factor and oscillation frequency range due to high source-drain turn-on resistance of transistors in capacitor switch units, which degrades performance and increases phase noise.
Innovation Solution
The oscillation circuit employs over-drive voltage to reduce turn-on resistance of switch transistors by using a level shifter to provide an enable voltage greater than the power voltage, coupled with a discharge circuit to manage node voltages and reduce parasitic capacitance, allowing for selective contribution of capacitors to total capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If transistors in capacitor switch units are turned on to contribute capacitance, then total capacitance increases and oscillation frequency decreases, but source-drain turn-on resistance serially couples to capacitors and quality factor decreases
Solution Approach 1:
The capacitor switch unit is segmented into two separate transistors (first transistor and second transistor) instead of using a single transistor. Each transistor connects to one capacitor, allowing independent control and reducing the impact of turn-on resistance on the overall capacitance contribution. This segmentation enables the capacitors to be effectively coupled to the oscillation node while minimizing resistance effects.
Solution Approach 2:
The patent applies different configurations to different parts of the capacitor switch unit. The first transistor and second transistor are positioned and connected differently within the circuit, with the first transistor connecting the first capacitor to the oscillation node and the second transistor connecting the second capacitor to the oscillation node. This local differentiation optimizes the capacitance contribution while managing resistance effects in specific regions of the circuit.
2Reliability
If transistor size is increased to reduce turn-on resistance, then quality factor improves, but parasitic capacitance increases and oscillation frequency range is limited
Solution Approach 1:
By segmenting the capacitor switch into two transistors, each transistor can be optimized independently. The transistors can be sized appropriately to achieve low turn-on resistance without excessive parasitic capacitance, as each transistor only needs to handle half the total capacitance switching task. This segmentation allows for better frequency response while maintaining quality factor.
Solution Approach 2:
The patent enables dynamic control of the capacitor switching through separate control signals for the first and second transistors. This dynamic control allows the oscillation frequency range to be extended by selectively enabling or disabling different capacitor combinations, adapting the total capacitance to achieve desired frequency ranges while maintaining optimal transistor sizing for quality factor.
3Adaptability or versatility
If smaller transistors are used, then parasitic capacitance decreases and oscillation frequency range expands, but turn-on resistance increases and quality factor degrades
Solution Approach 1:
The segmentation into two transistors allows each transistor to be smaller while collectively providing the necessary low turn-on resistance. Each smaller transistor has reduced parasitic capacitance, enabling wider frequency range, but the parallel configuration maintains low overall resistance for quality factor.
4Reliability
If over-drive voltage is applied to reduce turn-on resistance, then quality factor improves, but power consumption increases
Solution Approach 1:
By using two transistors instead of one, the voltage stress and current requirements are distributed. Each transistor operates at lower over-drive levels, reducing the overall power consumption while maintaining the quality factor improvement from reduced turn-on resistance.
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 enhances the quality factor, reduces phase noise, and extends the oscillation frequency range while maintaining low power consumption and noise isolation.
Implementation Method 1
the inductors L1 and L2, the capacitors CV1 and CV2 and the capacitor switch units Bp(1) to Bp(K) form an LC (inductance-capacitance) loading of the amplifier
Implementation Method 2
When the control signal Sp(k) equals the power voltage VDD to turn on the transistors T1(k) and T2(k)
Data Source
AI summary
An oscillation circuit and associated method, wherein the oscillation circuit provides a pair of oscillation signals at two oscillation nodes, and includes a first capacitor, a switch circuit and a second capacitor serially coupled between the two oscillation nodes; the switch circuit conducts between the first capacitor and the second capacitor on an enable voltage higher than a power voltage of the oscillation circuit.