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Proper measurement techniques and calibration methods can go a long way in evaluting the S-parameters of high-frequency, high-- speed analog and digital circuits.
Understanding how different S-parameters describe the behavior of analog and digital circuits can help engineers to accelerate the development of matching networks and high-frequency, high-speed components. A critical part of that understanding is knowing how to measure the S-- parameters of active and passive devices. This last installment of this four-part series on S-parameters will examine measurement techniques and discuss the importance of a good calibration.
S-parameters were developed to measure devices at high frequencies (i.e., above 1 GHz), and the vector network analyzer (VNA) was the test tool developed for the purpose of measuring the S-parameters of active and passive components and devices. Unfortunately, the connection between the VNA and the device under test (DUT) is never ideal and represents an impedance discontinuity.
To accurately account for the connections between the DUT and the VNA, a calibration must be performed.
Measurements are only as accurate as the equipment, methodology, and skill of the test-equipment operator. To ensure the most accurate S-parameter measurements possible, good test equipment and calibrations are required. Which calibration standards are used depends on the measurement setup. Some possible calibration standards are the short, open, load, and through (SOLT) that are provided in the Agilent model 85033D 3.5-mm calibration kit from Agilent Technologies (Santa Rosa, CA) or the impedance-standard substrate (ISS) made available by Cascade Microtech (Hillsdale, OR) for calibration of on-wafer measurements. Another option...