PLL VCO Gain Control Using Dual Charge Pumps and Filters
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Solution Overview
Problem
Existing PLL circuits face challenges in stabilizing the voltage controlled oscillator and reducing noise sensitivity, particularly due to the need for high capacitance values in filters and difficulties in matching the gain of different current paths, which increases circuit area and complexity.
Innovation Solution
A PLL circuit design incorporating first and second charge pump circuits, along with filters that operate with different currents, and a voltage control unit that generates voltage signals for both low and high gain inputs to the voltage controlled oscillator, allowing for reduced capacitance and stabilized operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If high capacitance values are used in filters to stabilize the voltage controlled oscillator, then the stability is improved, but the circuit area increases
Solution Approach 1:
The patent divides the single filter into two separate filters (first filter and second filter) that operate with different current values. The first filter uses a first current value while the second filter uses a second current value, allowing each filter to be optimized independently for stability while reducing the total capacitance required compared to a single high-capacitance filter.
Solution Approach 2:
The patent applies different current values to different parts of the filtering system. The first charge pump circuit operates with a first current value for its associated filter, while the second charge pump circuit operates with a second current value for its associated filter. This local differentiation allows optimal performance at each stage without requiring uniformly high capacitance throughout the circuit.
2Object-affected harmful factors
If multiple charge pump circuits operate with different currents, then noise sensitivity is reduced, but the difficulty in matching gain of different current paths increases
Solution Approach 1:
The patent employs a feedback mechanism where the output of the first filter is fed back through a second charge pump circuit to the input of the first filter. This feedback loop allows the system to automatically adjust and match the gains of different current paths, eliminating the need for complex external gain matching circuits while reducing noise sensitivity through the dual-current operation.
3Area of stationary object
If reduced capacitance is used in filters, then the circuit area is reduced, but the stability of the voltage controlled oscillator deteriorates
Solution Approach 1:
The patent segments the filtering function into two independent filters operating at different current levels. This segmentation allows the total capacitance to be distributed across two smaller capacitors rather than requiring one large capacitor, thereby reducing total circuit area while maintaining or improving stability through the dual-stage filtering approach.
Solution Approach 2:
The patent changes the operating current parameter between the two charge pump circuits and their associated filters. By operating the first charge pump circuit at a first current value and the second charge pump circuit at a second current value, the system achieves optimal stability and noise performance with reduced capacitance values compared to a single high-current operation mode.
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 noise sensitivity and circuit area by stabilizing the voltage controlled oscillator, enabling efficient operation with reduced capacitance and matching the gains of different current paths, thus improving the overall performance of the PLL circuit.
Implementation Method 1
a first filter that filters out a predetermined frequency component included in a signal generated according to a current output from the first charge pump circuit, and outputs the signal as a first voltage signal
Implementation Method 2
a second filter that inputs a current output from the second charge pump circuit and outputs a predetermined constant voltage as a second voltage signal
Implementation Method 3
a voltage controlled oscillator that has a first low gain property, a second low gain property, and a high gain property, and is controlled by the first voltage signal with the first low gain property, by the second voltage signal with the second low gain property, and by the third voltage signal with the high gain property, to generate an oscillating frequency according to the first to third voltage signals
Data Source
AI summary
A PLL circuit includes first and second charge pump circuits controlling an output voltage according to an output signal of a phase comparator, a first filter filtering out predetermined frequency component included in a signal generated according to current output from the first charge pump circuit, and outputting the signal as a first voltage signal, a second filter inputting a current output from the second charge pump circuit and outputting a predetermined constant voltage as a second voltage signal, a voltage control unit outputting a third voltage signal according to a comparison result between the first voltage signal output from the first filter and a reference voltage signal, and a voltage controlled oscillator that has a first low gain property, a second low gain property, and a high gain property, and is controlled by the first to third voltage signals to generate an oscillating frequency.