Bias-Tee VNA Calibration for DC-Biased RF Measurements
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Solution Overview
Problem
Existing vector network analyzer (VNA) calibration methods do not account for DC voltage effects, leading to measurement inaccuracies when characterizing devices that require biasing, as most calibration standards cannot handle dissipation power, resulting in parasitic effects that are not compensated.
Innovation Solution
A test and measurement system with a bias tee that couples a DC bias signal into the signal path during calibration with specific calibration standards, allowing for the calculation of error terms that account for DC signal influence, and applies these terms during device measurement to correct for inaccuracies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC bias signal is applied during calibration, then measurement accuracy for active devices is improved, but calibration standards cannot handle the dissipation power
Solution Approach 1:
The system performs a preliminary calibration without DC bias to establish baseline error terms, then performs a second calibration with DC bias applied to capture DC-related parasitic effects. This preliminary action allows the system to prepare the calibration standards before exposing them to dissipation power, and to process the measurements in a controlled sequence that mitigates the harmful effects of continuous DC power application.
Solution Approach 2:
The calibration process alternates between applying and removing the DC bias signal in periodic cycles. During each cycle, the DC bias is applied only for the duration needed to measure the calibration standards, then removed or reduced. This periodic application allows the system to capture DC-dependent error terms while limiting the total dissipation power exposure of the calibration standards over time.
2Measurement precision
If DC bias signal is applied during calibration, then parasitic effects are compensated, but calibration routine complexity increases
Solution Approach 1:
The calibration routine is segmented into distinct phases: a first calibration phase without DC bias and a second calibration phase with DC bias. Each phase measures specific error terms relevant to that condition. This segmentation allows the complex task of compensating for both AC and DC parasitic effects to be broken down into manageable, separately executable calibration routines that can be processed independently and then combined.
Solution Approach 2:
The measurement system is designed with multi-functionality to handle both AC-only calibration and AC+DC calibration modes using the same hardware infrastructure. The bias-tee and DC signal source can be configured to provide DC bias when needed, but the system universally supports both calibration approaches. This universality reduces overall system complexity by using a single platform that adapts to different calibration requirements rather than requiring separate dedicated systems.
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
This approach improves measurement accuracy by accounting for DC signal effects, reducing uncertainties in VNA measurements of active devices by incorporating DC bias signal considerations during calibration and measurement.
Implementation Method 1
at least one bias tee which is coupled to the signal path; wherein the bias tee comprises a DC input port which is configured to receive a DC bias signal, wherein the bias tee is arranged to couple the received DC bias signal into the signal path
Data Source
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AI summary
The invention relates to a test and/or measurement system (10). The test and/or measurement system comprises: an RF signal source (11) configured to generate an RF stimulus signal; a device port (13); a signal path (12) which is arranged to electrically connect the RF signal source (11) to the device port (13); a measurement unit (15) which is coupled to the signal path (12), wherein the measurement unit (15) is adapted for measuring the RF stimulus signal propagating via the signal path (12) to the device port (13) and a measurement signal received at the device port (13); and at least one bias tee (14) which is coupled to the signal path (12), wherein the bias tee (14) comprises a DC input port which is configured to receive a DC bias signal, wherein the bias tee (14) is arranged to couple the received DC bias signal into the signal path (12). The test and/or measurement system (10) is operable in a calibration mode during which at least four different calibration standards (40a-d) are alternately connected to the device port (13). The test and/or measurement system (10) is configured to couple the DC bias signal into the signal path (12) via the bias tee (14) during the connection of at least one of the calibration standards (40a-d), but not during the connection of all of the calibration standards (40a-d).