PLL-VCO Circuit Partitioning to Reduce Spurious Tones
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Solution Overview
Problem
Oscillator circuits employing phase locked loops (PLLs) face issues with spurious tones due to low isolation between PLL and voltage-controlled oscillator (VCO) circuitry, which limits performance and cannot always be filtered effectively.
Innovation Solution
An integrated circuit design that spatially isolates PLL and VCO circuitry on the same die, allowing for interconnection of two instances of the integrated circuit to reduce cross-coupling and spurious tones, while enabling calibration and control via a single interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If PLL and VCO circuitry are integrated on the same die with close proximity, then device complexity is reduced and integration is improved, but spurious tones increase due to low isolation and cross-coupling
Solution Approach 1:
The patent divides the oscillator system into two separate integrated circuit devices: a first integrated circuit containing the PLL circuitry and a second integrated circuit containing the VCO circuitry. This segmentation physically separates the two circuit blocks, reducing cross-coupling and spurious tone generation while maintaining integration benefits within each device.
Solution Approach 2:
The patent introduces an intermediary connection mechanism between the first and second integrated circuits, including control voltage output terminals, calibration input/output terminals, and interface circuitry. These intermediaries enable controlled interaction between the segmented PLL and VCO circuits while maintaining isolation to reduce spurious tones.
2Object-generated harmful factors
If two separate integrated circuits are used for PLL and VCO to reduce spurious tones, then spurious tone amplitude is reduced, but device complexity and interconnection requirements increase
Solution Approach 1:
The patent designs the interface circuitry between the two integrated circuits to serve multiple functions: controlling VCO calibration, providing reference signals, and enabling communication. The calibration circuitry and interface circuitry are designed to handle multiple operations through standardized terminals, reducing the overall complexity despite using separate devices.
3Ease of manufacture
If PLL and VCO are closely integrated, then ease of manufacture is improved, but isolation between circuits deteriorates leading to increased cross-coupling
Solution Approach 1:
By segmenting the design into two separate integrated circuits, the patent achieves physical isolation that eliminates substrate coupling and electromagnetic interference between PLL and VCO circuits, while each individual circuit remains manufacturable using standard IC fabrication processes.
Solution Approach 2:
The patent extracts the VCO circuitry from the same die as the PLL circuitry, placing it in a separate integrated circuit device. This extraction removes the source of cross-coupling and isolation problems while maintaining the functional integration of the overall oscillator system through controlled interconnections.
Data Source
AI summary
An integrated circuit includes phase locked loop (PLL) circuitry, voltage controlled oscillator (VCO) circuitry, and interface circuitry. The PLL circuitry includes a reference signal input terminal, a reference frequency divider circuit, a reference signal output terminal, a switch, a phase detector, a charge pump, and a control voltage output terminal. The reference frequency divider circuit is coupled to the reference signal input terminal. The switch is coupled to the reference frequency divider circuit and to the reference signal output terminal. The switch is configured to switchably connect the reference frequency divider circuit to the reference signal output terminal. The VCO circuitry includes a control voltage input terminal, a VCO, calibration circuitry, and a calibration input/output (I/O) terminal. The VCO is coupled to the control voltage input terminal. The calibration circuitry is coupled to the VCO. The calibration I/O terminal is coupled to the calibration circuitry.