Picotest Signal Injectors improve regulator, power supply test accuracy

(September 27, 2010) — Picotest released a new family of Signal Injectors, or adapters, to improve voltage regulator, LDO, and power supply testing accuracy. Increased bandwidth and higher resolution measurements are enabled for PSRR, stability, crosstalk, reverse transfer, input impedance, Bode plots, and crosstalk tests along with non-invasive in-circuit testing (ICT) for load transients, stability and output impedance. The Signal Injectors work with network analyzers, oscilloscopes, and arbitrary waveform generators from all manufacturers.

The family consists of two injection transformers, a DC bias injector, a line injector, a solid state voltage injector, and a unique solid state current injector along with cascadable attenuators.

“These signal injectors will change how engineers and IC manufacturers test voltage regulators and other power circuitry,” states Steve Sandler, managing director of Picotest.com. “Engineers currently connect their expensive network analyzers to devices under test (DUT) via poor performing test adapters, such as audio, video, or 60Hz transformers or home-brewed interconnect schemes. The data they get is often erroneous. In many cases, the data may look reasonable, but is not accurate.” The same is true of voltage regulator and LDO data sheets. “Much of what we find in the data sheet graphs is either incorrect or incomplete. The signal injectors solve these problems and allow analyzers and oscilloscopes to make higher resolution, higher bandwidth measurements to the point where the true circuit performance can be revealed.”

The J2111A current injector is capable of performing a small signal step loading at switching speeds and bandwidths that electronic loads cannot (40MHz, 20ns Rise/Fall times). The capacitance of an electronic load, which is generally too high and impacts the measurement, is not an issue for the current injector. Incorporating a 40MHz current monitor, the current injector can also be used to measure output impedance, as well as, the stability of a three-terminal regulator or a filter combined with the negative resistance of a switching converter or power supply. One of the key benefits is that load step, stability, and impedance measurements can all be made non-invasively while connected to hardware that is already integrated in its production form. For example, the control loop for a fixed output LDO cannot be broken and its stability directly measured since the loop is within the IC. Load step testing is currently the only way to check stability besides simulation. Such testing does not produce an exact phase margin result. While the J2111A current injector can perform the load step testing, it can also allow the output impedance to be recorded and from that, an exact phase margin result can be computed.

The J2120A line injector allows the input DC supply voltage to be modulated by the analyzer source signal, as in the case of a PSRR measurement. The line injector supports a frequency range that is generally well below the AC line frequency and above control loop bandwidths (10Hz-10MHz). The line injector is capable of operating levels that include 5 Amps maximum current and 50VDC maximum input voltage, while minimizing the power dissipation within the injector.

The injection transformers (J2100A 1Hz – 5MHz & J2101A 10Hz – 45MHz) and the J2110A Solid State Voltage Injector, also known as a Bode box, greatly extend the usefulness of any network analyzer for Bode plot tests. They enable network analyzers to better measure stability, input and output impedance, PSRR, component impedances, reverse transfer, crosstalk and Middlebrook filter stability. The J2100A, with its excellent low frequency performance, is ideal for PFC testing, while the J2101A is better suited for general power supply testing. When lower (DC) or higher bandwidths of up to 50MHz are needed, the J2110A solid state injector can be employed. The injection transformers each feature a 23 Octave range, low distortion for superior precision, and a 5 Ohm termination impedance for minimum impact to the loop.

The solid state voltage injector features a DC-45MHz bandwidth to support thermal and mechanical controls, as well as the highest performance regulators and amplifiers, low distortion for superior precision, 25 Ohm insertion resistance, 50 Ohm oscillator input, and less then 3uA typical bias current. A very high PSRR low noise power supply with universal input range is included.

The J2130A DC bias injector has a 10Hz-10MHz usable bandwidth and can easily measure varactors, junction capacitance, capacitors voltage sensitivity, as well as bias low power transistor amplifiers and diodes for parameter extraction.

While most engineers own a network analyzer, few own the necessary Signal Injectors to make accurate and repeatable high resolution measurements. With the Picotest family of signal injectors, you can make these measurements with confidence that your results will be accurate to the bandwidth and resolution levels necessary for your application.

The Signal Injectors are available from Picotest (www.Picotest.com) individually and in bundles.

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