TCXO Temperature Sensor Circuit for Low-Frequency Noise Reduction
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Solution Overview
Problem
Existing temperature sensors for temperature compensated crystal oscillators (TCXOs) suffer from poor noise performance, particularly at low frequencies, which affects the phase noise properties of the frequency reference.
Innovation Solution
A new transistor circuit design for temperature sensing, which includes a plurality of transistor circuits with bias circuits that reduce noise levels in the output temperature signals, and a delta-sigma modulator ADC to generate a temperature sensor signal dependent on the output signals from these circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional temperature sensors are used in TCXO, then temperature measurement function is provided, but noise performance deteriorates particularly at low frequencies
Solution Approach 1:
The temperature sensor is divided into multiple parallel transistor circuits (first transistor circuit, second transistor circuit, etc.), each contributing to the overall temperature measurement. This segmentation allows individual circuits to operate at optimized bias points, reducing noise while maintaining measurement accuracy through combined output.
Solution Approach 2:
The bias circuits are configured to operate transistors at specific current levels and temperatures to optimize the noise performance. By carefully controlling bias parameters (current, voltage, temperature), the sensor achieves low noise operation particularly at low frequencies while maintaining accurate temperature measurement capability.
2Object-generated harmful factors
If multiple transistor circuits are used to improve noise performance, then noise performance improves, but device complexity increases
Solution Approach 1:
Multiple transistor circuits are merged in parallel configuration, sharing common biasing structures and output combining mechanisms. This merging approach achieves noise reduction through diversified signal paths while minimizing the increase in overall circuit complexity by reusing common components and structures.
Solution Approach 2:
The transistor circuits are designed with universal characteristics where each circuit can function both as an independent temperature sensing element and as part of the combined parallel structure. The bias circuits serve multiple functions including noise reduction, temperature compensation, and signal conditioning, reducing the need for separate dedicated components.
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
The proposed solution achieves excellent noise performance, particularly at low frequencies, thereby improving the close-in phase noise of TCXOs, which is critical for communications technologies.
Implementation Method 1
each transistor circuit is arranged to output a temperature signal that is dependent on the temperature of the transistor comprised by the transistor circuit
Implementation Method 2
each bias circuit is configured such that the noise level in each output temperature signal is low; the transistor bias circuit is configured such that noise generated within the transistor is at least partially reduced by the bias circuit
Data Source
AI summary
Disclosed herein is a temperature compensated crystal oscillator, TCXO, comprising: a crystal oscillator arrangement configured to generate an output signal of the temperature compensated crystal oscillator; and a temperature sensor arranged to generate a temperature sensor signal, wherein the output signal of the crystal oscillator arrangement is controlled in dependence on the temperature sensor signal; wherein: the temperature sensor comprises a plurality of transistor circuits; each transistor circuit comprises a transistor and a bias circuit; each transistor circuit is arranged to output a temperature signal that is dependent on the temperature of the transistor comprised by the transistor circuit; each bias circuit is configured such that the noise level in each output temperature signal is low; and the plurality of transistor circuits are arranged so that the temperature sensor signal is dependent on each of the plurality of output temperature signals.