PLL Loop Filter Using Voltage Regulation for High PSRR Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Analog PLL circuits face challenges in integrating into digital noisy SoC environments due to susceptibility to noise, requiring a solution that maintains high power supply rejection ratio (PSRR) and stability while allowing for a wide tuning range.
Innovation Solution
Incorporating a voltage regulator-based filtering scheme that includes an RC network and a voltage follower within the PLL circuit, which enhances PSRR and loop stability, and allows for multiple control signals to improve oscillator performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional RC filter is used in the PLL circuit, then the circuit structure is simple, but the power supply rejection ratio (PSRR) is low and noise susceptibility is high in digital noisy SoC environments
Solution Approach 1:
The patent combines the voltage regulator module with the loop filter module into an integrated filter circuit. The voltage regulator module includes an error amplifier and a feedback network, while the loop filter module includes RC networks. This merging allows the circuit to benefit from both the high PSRR of voltage regulation and the noise filtering capabilities of the RC networks, resolving the contradiction between improving PSRR and maintaining structural simplicity.
Solution Approach 2:
The integrated filter circuit serves multiple functions: it acts as both a voltage regulator to reject power supply noise and a loop filter to smooth the control voltage for the VCO. The feedback network provides both voltage regulation and frequency response shaping. This multi-functionality allows a single circuit to address both PSRR requirements and loop filtering requirements without requiring separate dedicated circuits.
2Adaptability or versatility
If the PLL circuit is designed for wide tuning range, then the adaptability is improved, but the loop stability becomes difficult to maintain
Solution Approach 1:
The patent employs dynamic pole-zero compensation through the feedback network and RC networks. The feedback network includes capacitors and resistors that create frequency-dependent impedance, allowing the loop filter to adapt its characteristics across different operating frequencies. This dynamic behavior enables the maintenance of loop stability across a wide tuning range by automatically adjusting the frequency response characteristics.
Solution Approach 2:
The integrated filter circuit utilizes parameter changes in the feedback network and RC networks to maintain stability across different tuning conditions. The capacitive and resistive elements exhibit frequency-dependent behavior that automatically adjusts the loop characteristics. Additionally, the voltage regulator portion maintains stable operating points that facilitate wide frequency excursions while preserving loop closure stability.
3Reliability
If multiple control signals are generated for the oscillator, then the tuning range and phase noise performance are improved, but the device complexity increases
Solution Approach 1:
The feedback network in the voltage regulator module serves dual purposes: it provides voltage regulation feedback and simultaneously generates multiple control signals for the VCO. The network includes nodes that can drive different VCO control inputs, enabling both coarse and fine tuning functions as well as phase noise filtering without 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 effectively reduces jitter and noise, enabling the PLL circuit to operate over a wide tuning range with improved PSRR and phase noise performance.
Implementation Method 1
The RC network, coupled to the first input terminal, is configured to produce the first voltage signal at least in response to a first current signal applied to the first input terminal
Implementation Method 2
The RC network, coupled to the first input terminal, is configured to produce the first voltage signal at least in response to a first current signal applied to the first input terminal
Implementation Method 3
The first voltage follower, coupled to the output terminal, is configured to receive the first output signal, and generate a first filtered signal in response to the first output signal
Data Source
AI summary
A filter circuit includes an amplifier circuit, a resistor-capacitor (RC) network and a first voltage follower. The amplifier circuit has a first input terminal, a second input terminal and an output terminal. The amplifier circuit is configured to output a first output signal from the output terminal according to a first voltage signal at the first input terminal and a second voltage signal at the second input terminal. The RC network, coupled to the first input terminal, is configured to produce the first voltage signal at least in response to a first current signal applied to the first input terminal. The first voltage follower, coupled to the output terminal, is configured to receive the first output signal, and generate a first filtered signal in response to the first output signal.