New Industry Products

Signal Injectors Support Bode Plots and PSRR Testing on Popular Oscilloscopes

July 30, 2019 by Scott McMahan

Picotest released a new FRA Bundle of signal injectors that enables Bode plot (pictured above) and power supply rejection ratio (PSRR) measurements for Keysight, Rohde & Schwarz, Siglent, and Tektronix oscilloscopes.

"Traditionally Bode plots and PSRR measurements have been made on Vector Network (VNA) or Frequency Response Analyzers (FRA). But recently scope manufacturers have begun to add FRA features to oscilloscopes, expanding their measurement capabilities. While the software add-ons enable new FRA features, without our injectors end-users can't actually make the measurements" according to Steve Sandler, Picotest CEO. "The FRA bundle provides the signal injectors needed to connect the scope to the DUT."

The Picotest FRA Bundle offers critical support for Bode Plots and PSRR/PSMR measurement on oscilloscopes. It works with the

Tektronix 5 or 6 series oscilloscopes using the 5-PWR or 6-PWR software, and the Keysight InfiniiVision X-Series with the power measurements option.

FRA Bundle of signal injectors

The bundle also works with Rohde & Schwarz R&S RTM, RTA, and RTB oscilloscopes using the R&S®RTx-K36 FRA option and the Siglent SDS1000X-E-FG series scopes with the appropriate firmware and SAG/SDG AWG support.

The device's software options by themselves do not enable these control loop measurements. The stimulus signals from AWG or the oscilloscope to the power supply under test must be injected. They, therefore, require Picotest injectors. The FRA Bundle includes the J2100A injection transformer that enables Bode Plots.

However, without an injection transformer to break the control loop of the power supply, measurement is not possible, even though the software may be installed.

The J2100A works from 10Hz to 5MHz, high enough for most power supplies in a 23 Octave range. J2100A has low distortion and supports 5Ω terminations that have minimal loop impact.

The FRA bundle also includes the J2120A line injector, which enables PSRR measurements. It allows the combination of the ripple signal with the power rail voltage for injection into the DUT with a 10Hz to 10MHz usable bandwidth, low loss design, and 5As/50Vdc capability.

Picotest FRA Bundle setups

Breaking the loop is a required part of the Bode Plot based stability measurement. The J2100A achieves this to inject the stimulus signal from the oscilloscope. The J2101A is an available option for applications in the 10Hz to 45MHz range. For applications with either lower or higher bandwidths, the optional J2110A solid-state injector works from dc to well above 100MHz.

Picotest notes that while the Bode plot injection transformer is a very wideband adapter, it is not useful for measuring the ripple rejection (PSRR/PSMR) of a power supply or even an opamp. The company says that this is because the qualities that make the injection transformer perform so well also result in a transformer that is intolerant of dc current.

Even very small dc currents (5mA or less) can significantly diminish the signal capacity or even totally saturate the transformer. For this reason, the Picotest line injector (J2120A) is another essential test adapter. The J2120A line injector allows modulation of the input dc supply voltage by the oscilloscope's source signal output, as in a Bode plot measurement.

Summary of features:

  • Provides the essential support for Bode Plots and PSRR Measurement on popular oscilloscopes
  • J2100A enables Bode Plots; without an injection transformer you cannot break the control loop and therefore cannot make the measurement
  • 5MHz high enough for most power supplies - 23 Octave range - Low distortion - 5 Ohm termination, minimum loop impact
  • J2120A enables PSRR measurements; allows you to combine the ripple signal with the power rail voltage for injection into the DUT
  • 10Hz-10MHz usable bandwidth - Low loss design - 5 Amps maximum current - 50VDC max input
  • Optional: J2110A Solid State Injector is also available for improved frequency response and lower noise, DC-45MHz

The Picotest FRA Bundle is priced at $1,050 in single quantities.