Picotest P2102A Operator's manual
PDN Probes
Documentation
Version 1.31, February 2021
Copyright © 2014-2021 Picotest
All Rights Reserved
Trademarks
The Picotest logo and “Picotest PDN Probes” are trademarks of Picotest Corp.
PDN Cable ® is a registered trademark of Picotest Corp.
All other brand and product names mentioned herein are used for identification purposes
only and are registered trademarks, trademarks, or service marks of their respective holders.
Copyright notice
Except as permitted under the United States Copyright Act of 1976, no part of this publication
may be reproduced or distributed in any form or by any means, or stored in a data base or
retrieval system, without the prior written permission of Picotest Corp.
Information in this publication supersedes that in all previously published material.
Specifications are subject to change without notice.
Contact information
Corporate offices
1-877
914-PICO
Technical support e-mail
World Wide Web
https://www.picotest.com
Table of Contents
Chapter 1 - Overview......................................................................................................4
Welcome ...........................................................................................................................................4
What’s Included ...............................................................................................................................6
Documentation and Support .........................................................................................................6
Warranty............................................................................................................................................6
Calibration.......................................................................................................................................11
Chapter 2 –PDN Probes Usage .....................................................................................7
Introduction......................................................................................................................................7
Connecting the Probe to the Instrument.....................................................................................8
Making a Measurement............................................................Error! Bookmark not defined.
DC Blockers: When and Why to Use Them .............................................................................12
NISM Stability Measurement (VRTS3 Board) ..........................................................................12
2-Port Probe Applications............................................................................................................15
Regulator Load Step Testing (VRTS3 Board) ...........................................................................15
Low Impedance PDN Power Integrity Testing (VRTS3 Board) ...........................................16
Chapter 3 – Accessories and Specifications................................................................. 18
Specifications..................................................................................................................................18
Safety Information.........................................................................................................................19
Handling Information...................................................................................................................20
Cleaning...........................................................................................................................................20
Electrical Specifications ................................................................................................................21
DC Blockers Electrical Specifications ........................................................................................21
Overview 4
Chapter 1 - Overview
Welcome
Thank you for purchasing Picotest’s PDN ‘Browser’ probes.
The Picotest PDN probes are precision passive transmission line probes that support a
variety of measurements including impedance (1-Port Reflection and 2-Port Series and
Shunt-Through), 3-Port Voltage/Current, Step Load, Ripple, Noise, TDT/TDR, PCB
Resonances, Clock Jitter, and the Non-Invasive Stability Measurement (‘NISM’)123. The
probes have some significant advantages compared to active probes and other types of
passive probes.
The high-bandwidth, fixed-pitch probe tip design enables accurate measurements for a wide
variety of component and connector sizes. It eliminates the need for soldering SMA or coax
cables to your board and the risk of damaging fine copper pads or pulling up small
components. You can get connectivity to circuit boards and devices without connectors.
The probes can be used for ‘browser’ style measurement. For instance, if you have multiple
power rails across your board, the small form factor and easy probe tip placement enables
you to quickly browse the regulator outputs, allowing you to decide which rails need further
investigation. When coupled with NISM, you have a powerful tool for assessing the stability
of multiple power sources no matter the physical configuration.
1https://www.picotest.com/non-invasive-stability-measurement.html
2https://www.picotest.com/Power-Integrity-Book.html
3https://www.picotest.com/products_J202B.html
Overview 5
The P2102A 2-port probe comes with four (4) interchangeable, snap on, probe heads sizes
(1206, 0805, 0603, and 0402) allowing good connectivity to various component sizes. It also
comes in one of four attenuations (1X, 2X, 5X, or 10X). The probes are compatible with all
equipment including VNAs, oscilloscopes, and spectrum analyzers.
Impedance Measurement Demands New Probe Capabilities
High-speed applications put pressure on the measurement of power supply busses to
unprecedented frequencies. As an example, the measurement of PDN impedance for
FPGAs, ASICs, and high-speed digital devices generally requires the measurement of
impedance levels in the milliohm scale at frequencies exceeding 1GHz. Measuring the high-
speed step load response in power systems using 2-port impedance is difficult because of the
need to connect two 50Ω transmission lines to the output capacitor. To further compound
this difficult task, these measurements often need to be made in very small circuits such as
cell phones, solid state disk drives, and computer tablets, to name a few examples.
These revolutionary probes alleviate many of these challenges while maintaining the
precision 50Ω characteristics required for these types of measurements.
What is a Transmission Line Probe?
Transmission line probes are special types of passive probes that replace the high impedance
probe cable found in a traditional passive probe with a precision transmission line, that has a
characteristic impedance that matches the oscilloscope’s input (50Ω). This greatly reduces
the input capacitance to a fraction of a picofarad, minimizing the loading of high frequency
signals. The probes are referred to as ‘PDN’ probes, because of their effective use in
measuring the low and ultra-low impedances found in power distribution networks.
The input impedance of the Picotest probes remains nearly constant over their entire
frequency range. The probes are useful in applications that produce fast rising, narrow pulses
with amplitudes which exceed the dynamic range of active probes. They also tend to have
less parasitic effects on frequency response, so they are ideal for measuring impedance. By
providing a simple yet elegant and flexible solution to probing high-frequency signals,
Picotest’s transmission line probes preserve signal fidelity and allow high-bandwidth test
equipment to accurately measure circuit characteristics.
The probes are designed to work with the J2102B common mode transformer which
eliminates instrument DC ground loops.
P2102A 2-Port Probe Feature and Benefit Summary
•Supports Measuring:
Impedance, Transient Step Load, Ripple, Noise, TDT/TDR, 2-port
impedance, PCB resonances, Clock Jitter, and Non-invasive Stability
•Wide Bandwidth – 300MHz *
•Measures < 1mOhm *, Up to kOhms **
Overview 6
•Four (4) Interchangeable Probe Heads –- Sizes 1206, 0805, 0603, and 0402
•Various Attenuations – 1X for optimum sensitivity and SNR, 2X, 5X, and 10X.
Higher attenuation is for higher voltages, impedance, or reduced loading
•True 4-Point Kelvin Measurement
•Browsing capability greatly eases testing of multiple rails and repeat measurements
•Virtually no capacitive loading
•Includes PDN Cables® for ultra-high shield attenuation and ultra-low shield
resistance
•Rugged, ergonomic design; small form factor gets into tight places
•Supports Non-Invasive Stability Measurement (NISM)
•Supports the Extended Range 2-Port Shunt-Through measurement
* Calibration dependent
** Using the EXTENDED 2-port setup.
What’s Included
Your Picotest Probe kit (P2102A) includes the following:
•2-Port Probe with PDN Cables
•P2100A-CAL probe calibrator board
•Probe Case
Documentation and Support
This documentation details the use of various probes. Specifications for the individual
probes are also included.
The support section of Picotest’s web site, https://www.picotest.com/support.html,
contains additional documentation and various publications on testing power supplies,
regulators, and other equipment using the Picotest probes.
Warranty
Every Picotest product you buy from Picotest.com is backed by a 1-year manufacturer’s
warranty. For warranty service or repair this product must be returned to a service facility
designated by PICOTEST. Please contact your local service representative for further
assistance.
PDN Probes 7
Chapter 2 –PDN Probes Usage
Introduction
The PDN probes have a wide dynamic range and can measure up to various voltage levels
without distortion (see specifications table for the voltage ranges for different attenuations).
The low inherent noise enables the measurement of small input signals. The P2102A may be
used with any 50ohm instrument. It is bi-directional and can be used like a traditional probe
to record signals, as well as to inject stimulus (load step currents or EMI). The probe is
especially useful for VRM/stability measurements.
Usage notes:
•Variable pin compression means variable inductance and coupling. It is
recommended that the same pressure/pin depression be used for calibration and
actual testing. There may be an uncertainty of 100-200 pH.
•The resistors on the calibrator board are all 49.9 Ohms. Very small (1005) resistors
are used to stay out of the way of the pins and to present minimum parasitic
inductance.
•The 2-port SOLT fixture removal calibration works well for low impedance testing.
Consult your VNA’s or oscilloscope’s user manual for details on performing probe
calibration.
•Full 2-port calibration with isolation is important if you want measure inductance
values below a few nH.
PDN Probes 8
•Typical cable markers are placed on the cables/probe head for identifying the ports
and the probe head has an indent in the housing for the tip side while the ground
side is flat and smooth.
•It is recommended that the pads used for testing be oversized by 20% if possible, to
make it easier to land the probe. For instance, the calibrator pads are about 20%
oversized.
•Two 1-port probes are generally better than one 2-port probe for coupling and pin
length, but harder to use and generally requires probe holders.
Connecting the Probe to the Instrument and Making a
Measurement
Connect the SMA connector of the probe to the SMA connector on the instrument. If the
instrument has a BNC connector, then a SMA to BNC adapter is required.
For measurements on most instruments, configure the settings as follows:
•Input impedance of the channel = 50 Ω
•Unit = V
•Attenuation = 1:1
You can now place the signal and ground pins on the target measurement points in your
circuit.
The probe consists of the probe head for connection to the DUT, the probe cable, and SMA
connector(s). The 2-port probe has two SMA connectors, one for each port with a common
ground.
The probes have a standard SMA connectors on each port. Other connector options are
available for purchase.
PDN Probes 9
Figure 1: A 2-port measurement using the P2102A probe. Pressure is needed to seat the four
pins firmly in place. The probe head should match or be larger than the capacitor you are
measuring across. Two pins go on each side of the capacitor.
Figure 2: Two signal lines go on the positive side of the capacitor and two ground lines go
on the ground side of the capacitor.
PDN Probes 10
Figure 3: A 2-port measurement using a probe holder which can help supply even pressure
for the four pins.
PDN Probes 11
Calibration
Figure 4: P2100A -CAL probe calibrator board.
See your instrument’s user guide for calibration instructions. The calibration process can be
measurement (setup) dependent.
Figure 5: Performing an SOL calibration: Short (left), Open (center), and load (50 ohm,
right) calibration.
PDN Probes 12
DC Blockers: When and Why to Use Them
A coaxial DC Block (or Blocker) is used when DC isolation is required to protect sensitive
test equipment or RF circuitry. Since the probe impedance of 50 ohms would load low
impedance sources, it is often necessary to block any DC current. Either the J2130A DC bias
Injector or the P2130A DC Blocker can be used for this purpose. The P2130A has male and
female SMA connectors that allow it to be easily connected to the 1-Port and 2-Port probes.
An SMA to SMA cable, or an SMA to BNC cable can then be used to connect the probe to
the instrument.
Figure 6: The P2130A DC blocker, available separately.
The P2130A DC Blocker lets through frequencies between 500 Hz and 8 GHz while
simultaneously providing low insertion loss and excellent VSWR. Its maximum differential
(input – output) voltage is 50V.
Blocks can still damage RF equipment if voltages are exceeded at the instrument. The
blocking cap is VERY large to get to low frequency (4uF) so it can transfer a lot of energy.
That is one reason for the attenuating probes rather than the blocks.
NISM Stability Measurement (VRTS3 Board)
NISM is a powerful technique for measuring the stability of control loops. The NISM
software, embedded in commonly used VNAs, converts output impedance to phase margin.
This is extremely useful considering that many of today’s power ICs do not have their
control loops exposed, and in fact, in those cases, NISM is the only way to make an accurate
stability measurement.
In this case, the output impedance of a Voltage Reference is measured. The VNA, in this
PDN Probes 13
case the Bode 100, is used to measure the impedance at the output of the reference. The
impedance is then converted to Phase margin using a simple cursor measurement, as shown
below.
Figure 7: The P2102A 2-port probe in the 2-port shunt-through test setup is used to measure
the output impedance at the output capacitor of a power supply. This same test can be
performed on any power supply control loop including POLs, switchers, and linear
regulators. The software converts the output impedance to phase margin.
PDN Probes 14
Figure 8: Stability of the Infineon PS5401 at C42 is measured using NISM. Top graph is the
on and off state impedance. The bottom graph is the QTg waveform. The measurement
reveals the phase margin of the voltage reference to better than 71 degrees.
PDN Probes 15
2-Port Probe Applications
Regulator Load Step Testing (VRTS3 Board)
The 2-port probe can be used to transmit a load current step through one port, while
measuring the response from the other port, simultaneously. This is a great advantage when
browsing your board’s power rails, looking for problems and poor stability. All you have to
do is setup the load step range and then simply move the probe to the capacitor at the
output of each regulator IC in order to view the transient response.
In this example of a linear regulator load step test, the J2150A Harmonic comb is used as a
simple and portable square wave generator (one of its modes of operation). It drives the
Picotest J2111A current injector. This modulates the load current at the output of the
regulator when the probe is applied. The P2130A DC blocker may be needed so that the
scope does not load the output of the regulator.
The impedance and step load are measured in the same way. Load step testing does not get
any easier.
Figure 9: The step load response is shown on CH1 and the applied load step is shown on
CH3. The amount of ringing is related to the stability of the system.
PDN Probes 16
Low Impedance PDN Power Integrity Testing (VRTS3 Board)
This sample test measures the output impedance and stability of an LDO using a 2-port
probe and a common mode transformer.
The J2102B common mode transformer is essential here, as there is an instrument ground
loop which would otherwise distort the low frequency data. Therefore, it is generally
required for VNA 2-port measurements.
Figure 10: The 2-port probe setup for a 2-port impedance/stability measurement of an LDO.
In this case, NISM software is also used to convert the impedance measurement to phase
margin (stability). The J2102B common mode transformer is used to break the instrument
ground loop that impacts low frequency data.
PDN Probes 17
Figure 11: The impedance data is shown to the left. The group delay is shown on the right
and is converted to phase margin (stability) via a simple cursor measurement and the built-
in NISM software.
PDN Probes 18
Chapter 3 – Accessories and Specifications
Specifications
P2102A Specifications
Probe Voltage
and Impedance
for Different
Attenuations
Impedance: Maximum Tip voltage
50 ohms: 5 Vrms (1X Attenuation)
100 ohms: 8.9 Vrms (2X Attenuation)
250 ohms: 11 Vrms (5X Attenuation)
500 ohms: 14Vrms (10X Attenuation)
VNA Port Voltage *
5Vrms
4.45Vrms
2.2Vrms
1.4Vrms
Characteristic
Rating
Bandwidth
DC-300MHz **
Input C:
TBD
Maximum thru Current any Port
1Amp
Probe Connectors
SMA-Mini SMP - 1 meter length, BNC available as an
option
Interchangeable Probe Tip Size
Four (4) Included: 0402, 0603, 0805, and 1206
Insulation Resistance
20Mohms
Port to Port Isolation
TBD
Rise Time
350 ps
Operating Temperature
0 to 45° C (32° F to 104° F) at 80% Relative Humidity
Nominal Length with Cable
1 meter
Attenuation
1X, 2X, 5X, or 10X – Selected when purchased, NOT
Changeable
Probe Pitch
Fixed
Calibrator Board Resistor Rating
30mW (Supports 13dBm)
Maximum Relative Humidity
80% at 31° C max
Usage
Indoor
Altitude
3000 m (9850 feet)
Absolute Maximum Voltage
< 50VAC and 75VDC
Note: The specifications are subject to change without notice.
* The Maximum Port Voltage shown based on the specified maximum tip voltage. Consult
PDN Probes 19
your VNA’s manual to verify the VNA port voltage is below the ratings of your instrument.
** The actual bandwidth and minimum measurable impedance obtained are dependent on
calibration and your test setup.
Safety Information
To avoid personal injury and to prevent fire or damage to this product or products
connected to it, review and comply with the following safety precautions. Be aware that if
you use this probe assembly in a manner not specified, the protection this product provides
may be impaired. Only qualified personnel should use this probe assembly. Do not connect
the probe to any voltage that exceeds the maximum permissible input voltage specified in
the data sheet. Non-compliance with this instruction carries the risk of an electric shock.
Make sure not to cause any short circuits when performing measurements on sources with
high output currents. Short circuits may cause injuries or burns.
Risk of injury caused by pointed object
The pins of the probe are extremely pointed and can easily penetrate clothes and skin.
Therefore, handle the probe pins with great care. When transporting the probe, e.g. when
carrying it in a pocket or tool bag, always use the supplied case. To exchange a probe pin,
use tweezers or pliers to avoid injuries.
Use only grounded instruments
Do not connect the probe ground lead to a potential other than earth ground. Always make
sure the probe and the measurement instrument are grounded properly.
Observe probe ratings
Do not apply any electrical potential to the probe input which exceeds the maximum ratings
of the probe or the accessories connected to it. In a combination always the lower rating /
measurement category applies to both probe and accessories connected to it.
Do not operate with suspected failures
Refer to qualified service personnel.
Indoor use only
Do not operate in wet/damp environment. Keep product surfaces dry and clean. Do not
operate the product in an explosive atmosphere.
PDN Probes 20
Handling Information
Handle with care especially when fitted with the extra thin and sharp spring contact
tip to avoid any injury. Note that the probe cable is a sensitive part of the probe. Do
not damage through excessive bending or pulling. Avoid mechanical shock to this
product in general to guarantee accurate performance and protection.
Caution: To avoid equipment damage and/or severe injuries or death ensure that the
absolute maximum ratings defined in this manual are observed at all times and never
exceeded.
Cleaning
To clean the exterior of the probe, use a soft cloth moistened with either distillated water or
isopropyl alcohol. Before use allow the probe to dry completely.
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