Scope accessory adds two-port shunt-through impedance measurement

By Gina Roos, editor-in-chief

Picotest’s new J2161A  two-way wideband active splitter enables the two-port shunt-through impedance measurement on oscilloscopes. Traditionally, this measurement for power distribution network impedance in the microohm and milliohm range for power integrity verification has been performed on vector network analyzers (VNAs) or frequency response analyzers (FRAs).

The J2161A combined with the new J2102B  common mode transformer, A.K.A. a ground loop breaker (needed for the two-port measurement), support scopes with FRA software features that support two-port measurement. This includes oscilloscopes like the Tektronix Series 5 and 6 lines, which offer a software add-on (5/6-PWR) to enable the measurement in the frequency domain.

The J2161A supports a typical measurement bandwidth from 100 Hz to 500 MHz, and impedances down to 1 mOhm, which are scope dependent.

Since a ground loop exists in the two-port shunt-through configuration, which can significantly impact measurements, Picotest said the simplest method to eliminate it is by adding a wideband, low loss, tightly coupled common mode transformer to the measurement. The Picotest J2102B common mode transformer delivers a flat frequency response from 1 Hz to over 6 GHz, while maintaining 50-ohm input impedance for accurate, low-noise measurements. The J2102B supports PDN measurement, component measurement, PSRR testing, and other applications.  

The Picotest J2102B pairs with the J2161A as shown in the setup images. The transformer removes the ground loops associated with VNAs and oscilloscopes, which frequently occur in power integrity PDN measurements.

Picotest expects more instrument companies will pack more features and capabilities into their oscilloscopes, and FRA features like Bode plot, non-invasive stability, PSRR, and two-port impedance measurements, which will become more commonplace in scopes. Picotest’s FRA bundle  and the J2161A support these FRA features on the Tektronix Series 5/6 scopes.

The J2161A is priced at $1,995. The J2102B is available in two configurations: one with BNC connectors and one with N connectors. The price of the J2102B-BNC is $699 and the J2102B-N is $799. The J2102B is CE certified, while certification is in process for the J2161A.