February 15, 2020 Phoenix, AZ: Picotest.com, a leader in high resolution test and measurement equipment, has released a new 2-port ‘Browser’ probe especially designed for measuring power integrity applications including VRM (Voltage Regulator Module) impedance and stability and power distribution network (PDN) impedance. The probe comes with multiple interchangeable sized heads allowing fast and repeatable power rail testing capability.
“The increase in awareness of the critical nature of this measurement and the proper design of the PDN impedance is really timed well for the release of this probing solution,” stated Steve Sandler, CEO of Picotest and frequent Power Integrity industry lecturer. “The ability to measure low and ultra-low impedances combined with the browsing capability is unmatched. I believe this will enable many engineers to perform 2-port shunt-through impedance testing where they might have not had the opportunity or capability in the past.”
The P2102A can measure sub-milliohm power rail impedances up to bandwidths of 300MHz (dependent on calibration). The probe comes with four (4) swappable heads (1206, 0805, 0603, and 0402); sizes that match common output capacitor sizes. It is available in different attenuations (1X, 2X, 5X, and 10X). This allows flexibility for users to measure across a wide range of voltages.
The Picotest P2102A probe is a unique 50 ohm transmission line with a true 4-point connection (two signal lines and two ground lines). This precision supports a variety of measurements including impedance (2 port series and shunt-through), transient step load, ripple, noise TDT/TDR, and clock jitter. It has significant advantages compared with active probes and other types of passive probes. A powerful added benefit is that you can use Picotest’s non-invasive-stability measurement (NISM) algorithm, available in most VNAs, to assess the power supply’s stability at the same time as you assess the PDN.
In the past, performing PDN impedance measurement required soldering of coax or preparing the PCB with RF connectors for measurement. The P2102A is referred to as a ‘browser’ probe for its ability to easily and quickly be moved from point-to-point/rail-to-rail simply by reseating the probe points. The probe achieves low inductance at the tip to mitigate space constraints on a dense PCB, while eliminating the need to add additional SMA connections or other test points necessary for impedance measurements. It is especially useful when there are multiple rails to test. Repeated measurements are simplified because connection is by simply touching the tip to existing output capacitor pads. The rugged, ergonomic design and small form factor allows the user to get into tight places. The slim body with extended tips provides good visibility of the target. Picotest’s PDN Cable®, which reduces losses and errors in low impedance testing, is used to connect the probe to the instrument. In short, this 2-port P2102A probe is best suited for VRM, power plane, and decoupling measurements.
The 2-port probe also allows transient step load browsing since it can be used to transmit a load current step through one port, while measuring the voltage response from the other port, simultaneously.
The probe is compatible with all 50 Ohm instruments, including vector network analyzers (VNAs), oscilloscopes, and spectrum analyzers.
The probe is designed to work with the traditional 2-port shunt-through impedance setup, including the J2102B common mode transformer or J2113A ground isolator which eliminate the DC ground loop present on most instruments. A source power amplifier such as the OMICRON Lab B-AMP12 (OL000168) can help measure ultra-low impedance magnitudes.
The price of the P2102A includes a SOLT (short open load through) and isolation calibration board.
Background
High speed printed circuit board (PCB) design requires well designed power delivery networks (PDN) to support today’s FPGAs and custom mixed-signal ASICs. The PDN contains important impedance information that can tell a designer how a system will react to dynamic currents. Vendor information for a VRM’s output impedance is not generally available and not always accurate when it is. Further, measuring ultra-low impedance on multiple VRMs or a multi-topology VRM is a challenge for any design engineer. The 2-port shunt-through measurement is the gold standard for measuring output impedance in the sub-milliohm region. But it can be a challenging measurement. It is not always possible to make these measurements without direct SMA connections to the PCB when a designer makes these types of measurements with a VNA, the method of connecting the DUT requires attention to detail to ensure inductance is minimized to allow an accurate measurement. PDN problems are significant and costly. They can often require a board spin to fix. To get the most out of your VNA, you need to use the right probes and accessories to ensure your measurement is successful. With a browser probe like the P2102A you can quickly characterize multiple VRMs to ensure stability or even check if your model is accurate during your initial PDN design.
