Trl calibration
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This document describes the TRL calibration technique which involves measuring S-parameters of three device standards: a Thru, Reflect, and Line. It allows self-calibration without precise knowledge of the standards. Measurements of the Thru, Reflect, and Line standards are used to solve for 8 error terms. Key advantages are that it does not require accurate knowledge of standards or frequency, and removes switch errors from the calibration.
Trl calibration
- 1. TRL • Self Calibration – Don’t need precise info about Standards • Just Zo of line – Isolation/Leakage • Same as SOLT method – Determine Switch terms separately • Ratio out with 4 Receivers – This leaves 8 error terms – Only need S parameters of 3 independent standards to solve 1
- 2. (T)RL - Thru • Thru device Insertable Thru – Typically ports connected (Zero length line) – Can use Non-Zero length line L • Reference planes are at center of line L/2 L/2 • Useful on-wafer DUT • Measure 4 S-parameters – S11, S21, S12, S22 2
- 3. T(R)L - Reflect • High Reflect device – Short or Open – Don’t need to have model of device • Unless using this device to establish reference planes – Port 1 device must be equal to port 2 device • S11 = S22 • Measure 2 S-parameters – S11, S22 3
- 4. TR(L) - Line • Delay Line – Not required to know length accurately • Optimal length near odd multiple of λ/4 (90 ) • Avoid lengths near 0 or 180 or even multiples of λ/4 • Ideal phase length is between 30 and 150 (5:1 BW) • Use multiple lines to extend frequency • Measure 4 S-parameters – S11, S21, S12, S22 4
- 5. TRL • 10 S-parameter measurements taken – Thru (4), Reflect (2), Line (4) • 8 Unknowns – Actually only 7 due to ratios of b’s & a’s • Solve for Unknowns • Use additional information – Determine Propagation Constant (γ) of Line – Reflection Coefficients of Reflect Standards 5
- 6. TRL Advantages • Not necessary to know details of Stds (only Zo of Line) • Frequency does not need to be accurate, only repeatable • Easily used in non-coaxial media – Waveguide – Stripline • Zero length Thru a robust, well defined standard • Switch Errors are removed – Leakage – Mismatch – Repeatability 6