PLL Reference Current Compensation for PVT-Stable Frequency Tuning
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Solution Overview
Problem
Existing phase-locked loop (PLL) circuits are sensitive to process variations, power supply voltage changes, and temperature fluctuations, leading to reliability issues and increased power consumption.
Innovation Solution
A PLL circuit incorporating a phase and temperature-varying current (PT-VAR) circuit generates compensation currents with complementary-to-absolute temperature (CTAT), proportional-to-absolute temperature (PTAT), and PTAT characteristics to mitigate these variations, using a 3-input amplifier and current digital-to-analog converters (DACs) to adjust transconductance and resistors for optimal frequency tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PLL circuits are used, then the circuit structure is simple, but the circuit is sensitive to process variations, temperature fluctuations, and power supply voltage changes
Solution Approach 1:
The reference current generation circuit is segmented into multiple independent current sources: a first reference current source, a second reference current source with PTAT characteristic, and a third reference current source with CTAT characteristic. Each current source is independently controlled and combined to form the total reference current, allowing separate optimization and compensation of different temperature and process effects.
Solution Approach 2:
The invention changes the temperature dependence parameters of the reference current by combining currents with different characteristics. The second reference current source provides PTAT (proportional to absolute temperature) current, while the third provides CTAT (complementary to absolute temperature) current. By adjusting the weights of these currents through digital control, the total reference current can be made temperature-compensated or tuned to specific temperature characteristics.
2Reliability
If compensation circuits are added to mitigate variations, then reliability improves, but power consumption increases
Solution Approach 1:
The invention implements dynamic control of the reference current components through digital-to-analog converters (DACs). The weights of the PTAT and CTAT current components can be dynamically adjusted based on operating conditions, allowing the circuit to optimize between compensation accuracy and power consumption. The controller can select different compensation strategies depending on temperature range, process corner, and application requirements.
Solution Approach 2:
The circuit changes the operational parameters of the current sources by controlling their activation and weighting. Instead of always running all compensation circuits at full power, the system can adjust the contribution of each current source (first, second, and third reference current sources) based on actual needs, reducing unnecessary power consumption while maintaining reliability.
3Reliability
If multiple reference current sources with different temperature characteristics are used, then temperature compensation improves, but circuit area increases
Solution Approach 1:
The invention merges multiple reference current sources (first, second, and third) into a single unified reference current generation circuit. The currents from different sources are combined through current mirrors and summation nodes to produce the total reference current. This integrated approach achieves temperature compensation without requiring separate physical circuits for each current source, optimizing area utilization.
Solution Approach 2:
The reference current generation circuit is designed to perform multiple functions simultaneously: generating the base reference current, providing temperature compensation through PTAT and CTAT components, enabling digital tuning of current weights, and maintaining stability across process variations. This multi-functionality is achieved within a single circuit block rather than requiring separate dedicated circuits for each function.
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 solution reduces the PLL's sensitivity to process, voltage, and temperature variations, improving reliability, reducing power consumption, and minimizing circuit area.
Implementation Method 1
a first compensation current based on PMOS and NMOS transistors and having a complementary-to-absolute temperature (CTAT) characteristic
Implementation Method 2
a second compensation current based on a PMOS transistor and having a proportional-to-absolute temperature (PTAT) characteristic, and a third compensation current based on an NMOS transistor and having a PTAT characteristic
Implementation Method 3
a current digital-to-analog converter (DAC) circuit configured to convert the reference current into a control current based on a digital code
Data Source
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AI summary
Example embodiments are directed to a phase-locked loop (PLL) circuit that includes a reference current generation circuit including a PT-VAR circuit. The PT-VAR circuit generates a compensation current to compensate for process variations, temperature changes, and/or power supply voltage changes in the PLL circuit, and the reference current generation circuit outputs the compensation current as a reference current. The PLL circuit further includes a current digital-to-analog converter (DAC) circuit that converts the reference current into a control current based on a digital code, and a VCO that generates a signal based on the control current. The compensation current is a sum of a first compensation current based on PMOS and NMOS transistors and having a complementary-to-absolute temperature (CTAT) characteristic, a second compensation current based on a PMOS transistor and having a proportional-to-absolute temperature (PTAT) characteristic, and a third compensation current based on an NMOS transistor and having a PTAT characteristic.