VCO Tuning Circuit for Accurate Phase Noise Testing
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Solution Overview
Problem
Integrated voltage-controlled oscillators (VCOs) in RF devices face challenges in testing, particularly in accurately assessing phase noise power, which affects the signal-to-noise ratio of RF signals, due to the inability to isolate intrinsic VCO characteristics from noise introduced by the tuning voltage.
Innovation Solution
The integration of switchable resistor networks and a control circuit in the VCO allows for selective activation of different voltage levels at the tuning input, enabling low-noise voltage generation and isolation of intrinsic VCO noise during testing, using automatic test equipment to control the resistor networks and set specific voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the VCO is tested using conventional methods without additional circuitry, then the testing process is simple, but the measurement precision of phase noise power is insufficient due to inability to isolate intrinsic VCO noise from tuning voltage noise
Solution Approach 1:
The patent segments the voltage control path into multiple independent resistor networks (first switchable resistor network and second switchable resistor network), each connected to different voltage nodes. This segmentation allows separate control and characterization of different voltage contributions to the VCO tuning input, enabling isolation of intrinsic VCO noise from tuning voltage noise during phase noise measurements.
Solution Approach 2:
The patent introduces switchable resistor networks as intermediary elements between the voltage nodes and the VCO tuning input. These resistor networks act as mediators that can be selectively activated to control the voltage applied to the VCO, allowing the testing circuit to isolate and measure different noise components. The switches and resistors form an intermediary layer that enables precise control over the tuning voltage during testing.
2Measurement precision
If switchable resistor networks are added to enable accurate VCO testing, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The switchable resistor networks serve multiple functions: they act as voltage dividers, noise isolation elements, and test configuration switches. The same circuit structures enable both normal VCO operation and accurate phase noise measurement by simply changing the switch states. This multi-functionality reduces the need for separate dedicated test circuitry, thereby limiting the increase in device complexity while still achieving improved measurement precision.
Solution Approach 2:
The patent changes the electrical parameters (resistance values, switch states, voltage levels) of the resistor networks to achieve different testing configurations. By adjusting these parameters, the circuit can isolate different noise components and characterize various VCO performance aspects without requiring physically different circuit structures for each measurement mode.
3Reliability
If the tuning voltage noise is not isolated, then the circuit operation is straightforward, but the reliability of phase noise measurement deteriorates due to contamination from tuning voltage noise
Solution Approach 1:
The patent extracts the tuning voltage noise component from the total measured noise by using switchable resistor networks to selectively apply different voltage sources. By taking out the tuning voltage contribution through controlled activation of specific resistor networks, the intrinsic VCO phase noise can be measured independently, significantly improving measurement reliability.
Solution Approach 2:
The patent employs dynamic switching of resistor networks during the testing process. The switches allow the circuit to transition between different configurations - enabling normal operation mode and precise measurement mode as needed. This dynamic reconfiguration enables the circuit to adapt to different testing requirements, improving reliability when measurements are performed while maintaining straightforward operation during normal function.
Data Source
AI summary
An integrated circuit is described herein. In accordance with one embodiment, the circuit includes a voltage controlled oscillator (VCO) that is configured to receive a tuning voltage at a tuning input and to provide an RF oscillator signal at an oscillator output. The circuit further includes a first and a second switchable resistor network. The first switchable resistor network includes at least a first resistor and at least a first switch and is connected between the tuning input of the VCO and a first node, which operably provides a first voltage. The second switchable resistor network includes at least a second resistor and at least a second switch and is connected between the tuning input of the VCO and a second node, which operably provides a second voltage. Furthermore, the circuit includes a control circuit that is configured to activate, dependent on a control signal, either the first switchable resistor network, the second switchable resistor network or both, the first and the second resistor networks.