TCXO Signal Buffer Using Lightly Doped MOS Transistors
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Solution Overview
Problem
The integration of multiple features in portable devices like smartphones requires separate temperature compensated crystal oscillators (TCXOs) due to the difficulty in buffering their output signals, which are expensive and contribute to increased device complexity and cost.
Innovation Solution
An integrated semiconductor electronic device with a lightly doped substrate and MOS transistors configured to buffer TCXO signals, reducing noise and damping, and using a specific MOS transistor structure with parallel branches and resistors to minimize output resistance and noise characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate TCXOs are used for each feature, then signal stability and precision are improved, but device complexity and cost increase
Solution Approach 1:
The patent merges multiple TCXO buffer functions into a single integrated buffer device. The buffer device includes a first MOS transistor for receiving the TCXO output signal and a second MOS transistor for supplying current, with both transistors sharing a common lightly doped substrate. This integration allows one buffer device to support multiple features, reducing the number of separate TCXOs and associated buffer circuits needed in the portable device.
Solution Approach 2:
The buffer device is designed with universal functionality to serve multiple features. The first MOS transistor can buffer signals for different features (e.g., GPS, WLAN, Bluetooth) by switching its connection to different second MOS transistors, each supplying current for a specific feature. This multi-functional design allows a single buffer device structure to replace multiple dedicated buffer circuits.
2Ease of operation
If TCXO output signals are buffered using conventional methods, then signal distribution is improved, but signal damping and noise increase
Solution Approach 1:
The patent changes the doping concentration parameter of the substrate to create a lightly doped substrate with doping concentration of 10^16 to 10^18 atoms/cm³, which is significantly lower than conventional substrates. This parameter change reduces the substrate's interaction with the TCXO signal, minimizing signal damping and noise. The low doping concentration ensures the substrate does not interfere with the high-frequency, low-voltage-swing TCXO output signals while still providing mechanical support.
3Reliability
If multiple separate TCXOs are integrated, then each feature gets dedicated clock signal, but manufacturing cost increases
Solution Approach 1:
The patent merges multiple TCXO buffer functions into a single integrated buffer device structure. By sharing the first MOS transistor and its lightly doped substrate across multiple features, the manufacturing cost per feature is reduced. The shared structure reduces the total number of transistors, substrates, and interconnections needed compared to having separate buffer devices for each TCXO.
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 solution allows for the reduction in the number of separate TCXOs, lowering overall device costs and complexity while maintaining signal stability and precision.
Implementation Method 1
a first MOS transistor (NVT11) configured to receive an output signal of a temperature compensated crystal oscillator (TCXO) at a control gate for providing the buffered TCXO signal at an output node
Implementation Method 2
An integrated semiconductor electronic device with a substrate having a first doping concentration is provided. The first doping concentration is a light doping, which means the concentration is for example about 108/cm2 or between 107/cm2 and 109/cm2
Data Source
AI summary
A buffer is provided. The buffer includes a buffering stage that receives an enable signal and an input signal and that provides an output signal and a bandgap stage that is coupled to the buffering stage and that is activated and deactivated by the enable signal. In particular, the buffering stage includes a buffering substage that includes a buffering transistor that is coupled to the input stage, wherein the buffering transistor is formed on a substrate, and wherein the buffering transistor has a channel with a doping concentration that is approximately the same as the substrate.