Tektronix P7700 Series TriMode Probes Reference manual

P7700 Series TriMode™ Probes
Technical Reference

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TriMode and TekFlex are trademarks of Tektronix, Inc.

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Warranty

Warranty

Tektronix warrants that this product will be free from defects in materials and workmanship for a period of one (1) year from the date of
shipment. If any such product proves defective during this warranty period, Tektronix, at its option, either will repair the defective product
without charge for parts and labor, or will provide a replacement in exchange for the defective product. Parts, modules and replacement
products used by Tektronix for warranty work may be new or reconditioned to like new performance. All replaced parts, modules and
products become the property of Tektronix.

In order to obtain service under this warranty, Customer must notify Tektronix of the defect before the expiration of the warranty period
and make suitable arrangements for the performance of service. Customer shall be responsible for packaging and shipping the defective
product to the service center designated by Tektronix, with shipping charges prepaid. Tektronix shall pay for the return of the product to
Customer if the shipment is to a location within the country in which the Tektronix service center is located. Customer shall be responsible
for paying all shipping charges, duties, taxes, and any other charges for products returned to any other locations.

This warranty shall not apply to any defect, failure or damage caused by improper use or improper or inadequate maintenance and care.
Tektronix shall not be obligated to furnish service under this warranty a) to repair damage resulting from attempts by personnel other
than Tektronix representatives to install, repair or service the product; b) to repair damage resulting from improper use or connection to
incompatible equipment; c) to repair any damage or malfunction caused by the use of non-Tektronix supplies; or d) to service a product
that has been modified or integrated with other products when the effect of such modification or integration increases the time or difficulty
of servicing the product.

THIS WARRANTY IS GIVEN BY TEKTRONIX WITH RESPECT TO THE PRODUCT IN LIEU OF ANY OTHER WARRANTIES, EXPRESS
OR IMPLIED. TEKTRONIX AND ITS VENDORS DISCLAIM ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR
A PARTICULAR PURPOSE. TEKTRONIX' RESPONSIBILITY TO REPAIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND
EXCLUSIVE REMEDY PROVIDED TO THE CUSTOMER FOR BREACH OF THIS WARRANTY. TEKTRONIX AND ITS VENDORS WILL
NOT BE LIABLE FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER
TEKTRONIX OR THE VENDOR HAS ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES.

[W2 – 15AUG04]

P7700 Series TriMode™ Probes Technical Reference 3

Table of Contents

Table of Contents

Warranty........................................................................................................................................................................................3

List of Figures................................................................................................................................................................................5

List of Tables................................................................................................................................................................................. 7

Important safety information..........................................................................................................................................................8

General safety summary........................................................................................................................................................8

Terms in the manual...............................................................................................................................................................8

Terms on the product............................................................................................................................................................. 8

Symbols on the product......................................................................................................................................................... 9

Theory of operation..................................................................................................................................................................... 10

Introduction.......................................................................................................................................................................... 10

Probe components........................................................................................................................................................10

Probe input architecture................................................................................................................................................13

Probe input architecture with the P77C292MM SMA adapter...................................................................................... 15

TriMode operation................................................................................................................................................................16

Operating voltages...............................................................................................................................................................17

Input voltage ................................................................................................................................................................ 18

Operating voltage window.............................................................................................................................................18

Input signal dynamic range...........................................................................................................................................20

Offset voltage................................................................................................................................................................21

Operating voltage window (P77C292MM SMA adapter).............................................................................................. 24

Improving measurement accuracy.......................................................................................................................................25

DSP correction filtering................................................................................................................................................. 25

DC probe compensation............................................................................................................................................... 25

Solder-in tip connection wire length..............................................................................................................................26

Using offset voltage to extend TekFlex® solder-in tip input voltage range................................................................... 28

Making single-ended measurements using the P77BRWSR differential probe tip.......................................................29

Temperature compensation.......................................................................................................................................... 30

Solder tip measurement configuration.......................................................................................................................... 30

Skew measurements of differential signals...................................................................................................................31

Reference....................................................................................................................................................................................32

Single-ended measurements............................................................................................................................................... 32

Differential measurements................................................................................................................................................... 33

Common-mode rejection ratio.......................................................................................................................................33

Assessing CMRR error................................................................................................................................................. 34

Input impedance effects on CMRR...............................................................................................................................34

Differential-mode rejection............................................................................................................................................34

Channel isolation.......................................................................................................................................................... 34

Specifications.............................................................................................................................................................................. 36

Warranted characteristics.................................................................................................................................................... 36

Typical characteristics..........................................................................................................................................................38

Host instrument firmware............................................................................................................................................................ 48

Index........................................................................................................................................................................................... 49

P7700 Series TriMode™ Probes Technical Reference 4

List of Figures

List of Figures

Figure 1: P7700 Series TriMode probe components...................................................................................................................10

Figure 2: TekFlex active probe tips............................................................................................................................................. 12

Figure 3: P77C292MM adapter...................................................................................................................................................12

Figure 4: P7700 Series TriMode probe input architecture...........................................................................................................13

Figure 5: P7700 Series TriMode probe input architecture with the P77C292MM SMA adapter................................................. 16

Figure 6: TriMode input structure................................................................................................................................................ 17

Figure 7: TekFlex probe tip inputs............................................................................................................................................... 18

Figure 8: Operating voltage window (TekFlex solder-in tips)...................................................................................................... 19

Figure 9: Dynamic range versus linearity at the probe amplifier step gain settings.................................................................... 20

Figure 10: Operating voltage window (P77BRWSR )..................................................................................................................20

Figure 11: Dynamic range linearity error plot.............................................................................................................................. 21

Figure 12: Simplified diagram of the TekFlex probe tip input network.........................................................................................22

Figure 13: Probe setup configuration menu................................................................................................................................ 23

Figure 14: Simplified Auto Offset circuitry .................................................................................................................................. 24

Figure 15: Operating voltage window (P77C292MM SMA adapter)........................................................................................... 24

Figure 16: Operating voltage window (differential mode, P77C292MM adapter)........................................................................25

Figure 17: Operating voltage window (common mode, P77C292MM adapter).......................................................................... 25

Figure 18: P77STFLXA solder tip attached with 10 mils (0.250 mm) wires (rise time = 30.5 ps)............................................... 26

Figure 19: P77STFLXA solder tip attached with 75 mils (1.90 mm) wires (rise time = 27.9 ps)................................................. 27

Figure 20: P77STFLXA solder tip attached with 120 mils (3.05 mm) wires (rise time = 30.1 ps)............................................... 27

Figure 21: P77STFLXA solder tip attached with 200 mils (5.08 mm) wires (rise time = 34 ps).................................................. 27

Figure 22: P77STFLXA solder tip attached with 300 mils (7.62 mm) wires (rise time = 42.8 ps)............................................... 28

Figure 23: Simplified diagram of the TekFlex probe tip input network.........................................................................................29

Figure 24: Differential input mode signal voltage and offset voltage...........................................................................................30

Figure 25: Solder tip measurement configuration....................................................................................................................... 31

Figure 26: Example of LVDS differential signal........................................................................................................................... 31

Figure 27: Simplified model of a differential amplifier..................................................................................................................33

Figure 28: Typical CMRR............................................................................................................................................................34

Figure 29: Typical channel isolation............................................................................................................................................35

Figure 30: P77STCABL differential impedance...........................................................................................................................44

Figure 31: P77STCABL SE impedance ..................................................................................................................................... 44

Figure 32: P77STFLXA differential impedance...........................................................................................................................45

P7700 Series TriMode™ Probes Technical Reference 5

List of Figures

Figure 33: PST77FLXA SE impedance.......................................................................................................................................45

Figure 34: P77BRWSR differential impedance........................................................................................................................... 45

Figure 35: Differential mode P77STCABL and P77FLXA equivalent circuit diagram................................................................. 46

Figure 36: Single-ended P77FLXA equivalent circuit diagram....................................................................................................46

Figure 37: Differential mode P77STFLXB equivalent circuit diagram......................................................................................... 46

Figure 38: Single-ended P77STFLXB equivalent circuit diagram............................................................................................... 46

Figure 39: P77BRWSR equivalent circuit diagram with 50 mil spacing...................................................................................... 47

Figure 40: P77BRWSR equivalent circuit diagram with 200 mil spacing.................................................................................... 47

P7700 Series TriMode™ Probes Technical Reference 6

List of Tables

List of Tables

Table 1: Probe tip attenuation factors..........................................................................................................................................14

Table 2: Rise time and overshoot degradation versus lead length..............................................................................................28

Table 3: Single-ended dynamic and offset ranges...................................................................................................................... 32

Table 4: Electrical characteristics................................................................................................................................................ 36

Table 5: Environmental characteristics........................................................................................................................................37

Table 6: Typical electrical characteristics.................................................................................................................................... 38

Table 7: Typical electrical characteristics for P77xx probes........................................................................................................ 39

Table 8: Electromagnetic compatibility (EMC) ............................................................................................................................43

P7700 Series TriMode™ Probes Technical Reference 7

Important safety information

Important safety information

This manual contains information and warnings that must be followed by the user for safe operation and to keep the product in a safe
condition.

General safety summary

Use the product only as specified. Review the following safety precautions to avoid injury and prevent damage to this product or any
products connected to it. Carefully read all instructions. Retain these instructions for future reference.

This product is not intended for detection of hazardous voltages.

To avoid fire or personal injury

Observe all terminal ratings To avoid fire or shock hazard, observe all rating and markings on the product. Consult the product manual

for further ratings information before making connections to the product.

Do not apply a potential to any terminal, including the common terminal, that exceeds the maximum rating
of that terminal.

Do not operate without covers Do not operate this product with covers or panels removed, or with the case open. Hazardous voltage

exposure is possible.

Avoid exposed circuitry Do not touch exposed connections and components when power is present.

Do not operate in wet/damp
conditions

Do not operate in an explosive
atmosphere

Keep product surfaces clean
and dry

Be aware that condensation may occur if a unit is moved from a cold to a warm environment.

Remove the input signals before you clean the product.

Probes and test leads

Remove all probes, test leads and accessories that are not in use.

Inspect the probe and
accessories

Use only the specified replacement parts.

Before each use, inspect probe and accessories for damage (cuts, tears, or defects in the probe body,
accessories, or cable jacket). Do not use if damaged.

Terms in the manual

These terms may appear in this manual:

Warning:

CAUTION: Caution statements identify conditions or practices that could result in damage to this product or other property.

Warning statements identify conditions or practices that could result in injury or loss of life.

Terms on the product

These terms may appear on the product:

• DANGER indicates an injury hazard immediately accessible as you read the marking.

• WARNING indicates an injury hazard not immediately accessible as you read the marking.

P7700 Series TriMode™ Probes Technical Reference 8

• CAUTION indicates a hazard to property including the product.

Symbols on the product

When this symbol is marked on the product, be sure to consult the manual to find out the nature of the potential hazards and
any actions which have to be taken to avoid them. (This symbol may also be used to refer the user to ratings in the manual.)

The following symbols may appear on the product:

Important safety information

P7700 Series TriMode™ Probes Technical Reference 9

Theory of operation

Theory of operation

Introduction

The P7700 Series TriMode Probes are designed for use with MSO/DPO70000C and newer oscilloscopes. Four P7700 Series TriMode
Probe models are available with bandwidths from 8 GHz to 20 GHz. MSO/DPO70000C oscilloscope models are available at comparable
bandwidths. These probe and oscilloscope models feature the high performance TekConnect intelligent probe interface. P7700 Series
probes must be operated with an attached P7700 Series probe tip. Several TekFlex tip models are available to support different application
requirements.

The P7700 Series probes and probe tips contain device-specific S-parameter data that, when transferred to the host oscilloscope after
the initial connection is made, create unique system DSP filters. These DSP filters optimize high frequency performance of the probe and
probe tip signal path.

The P7700 Series probes are optimized for high bandwidth; they are not general-purpose probes. The P7700 Series probe solder tips that
can be used with the probes are miniaturized for electrical characteristics and access to dense circuitry, and must be handled carefully.

Figure 1: P7700 Series TriMode probe components

Probe components

P7700 Series probes are comprised of a probe compensation box (comp box), a TekFlex connector for attaching probe tips, and an
interconnect cable that transfers measured signals, power, and control signals between the probe comp box and the TekFlex connector
probe head. A TekFlex probe tip must be inserted into the TekFlex connector probe head to make the final connection to the DUT (device
under test).

Probe compensation box

The probe compensation box assembly mates to the host instrument through an intelligent TekConnect probe interface. Power, control
signals, and the signal measured by the probe are transferred to and from the oscilloscope through the TekConnect interface. The comp
box includes a button to select the TriMode input mode for probe tips that support TriMode functionality:

P7700 Series TriMode™ Probes Technical Reference 10

Theory of operation

• Differential (A–B)

• A input (single-ended to ground)

• B input (single-ended to ground)

• Common-mode ((A+B)/2 to ground)

The probe input mode can also be selected using the oscilloscope Probe Setup configuration menu. The Probe Setup configuration menu
is also used to adjust the probe Offset A and Offset B voltage settings and to initiate a DC Probe Compensation operation. All other
P7700 Series probe internal controls, such as vertical scaling, are handled automatically through communication between the probe and
oscilloscope.

An LED on the top panel of the comp box indicates the selected input mode. Another LED indicates when a warning condition exists.
Warnings are caused when parameters such as input voltages exceed the safe limits of the probe.

A mechanical latch and optional retention thumbscrew hold the probe securely to the instrument during use. The thumbscrew is only
intended to be finger-tightened, and is machined to prevent tools from being used to over-torque it. To remove the probe, loosen the
thumbscrew counterclockwise, depress the latch button to release the probe, and then pull out the probe.

CAUTION: To prevent damage to the probe, use care when handling the probe. Rough or careless use can damage the probe.

Main interconnect cable

This cable assembly consists of a pair of matched, low-loss coaxial signal cables that carry the acquired signal from the probe head to the
probe comp box. The cable assembly includes an 8-conductor bundle of wires that supply probe tip head power and control signals from
the probe comp box through the TekFlex connector interface. Some of the wires carry bidirectional data, such as queries and responses
about the type of probe tip attached to the TekFlex connector, and other probe tip-specific information.

TekFlex™ connector

The new TekFlex connector technology combines a high speed signal path with low speed control signaling in a single, easy to connect
accessory connector. The TekFlex connector has a pinch-to-open design that when open requires minimal force to attach an accessory tip.
When the TekFlex connector is closed, it provides a secure connection to the accessory to avoid accidental disconnections.

The connector provides a light-weight electrical and mechanical interface between a P7700 Series probe and a TekFlex active probe tip. It
contains a spring-loaded set of electrical contacts that connect between the main cable wiring and contact patterns on the attached probe
tip. There is a differential, high-frequency contact pattern on the top of the probe tip that connects the probe tip dual signal inputs and
grounds to the probe main cable coaxial pair. There is also an eight-finger contact pattern on the bottom of the probe tip that connects the
probe tip power and control signals to a ribbon wire in the main cable. The TekFlex connector provides mechanical alignment between a
keyed hole pattern on the probe tip and a pair of pins inside the spring loaded connector housing.

With the TekFlex connector, the P7700 series probes offer a set of active probe tips with the probe's buffer amplifier only millimeters from
the input connections. The short signal path enabled with the active tips provides high fidelity and a high impedance input. It minimizes
signal loss, capacitance, and additive noise.

Probe tips

The probe tips are automatically detected and displayed in the Probe Setup screen .

P7700 Series TriMode™ Probes Technical Reference 11

Theory of operation

Figure 2: TekFlex active probe tips

TekFlex solder-in tips

These tips use flex circuit material and provide soldered, multi-point connections. They support full TriMode measurement capabilities and
full probe bandwidth. If care is taken during the soldering process, these probe tips can be reused through multiple soldering operations.
The small size and low cost design are good for high interconnect density measurements.

The P77STFLXA Flex circuit based solder tip and P77STFLXB, P77STFLRB, P77HTFLRB Flex circuit based DDR memory solder tips are
available.

The first time the probe tip is detected, S-parameter data for the probe tip is sent to the oscilloscope, and probe-tip specific DSP filters are
generated. These filters improve the measurement accuracy of high-frequency measurements.

P77STCABL

This optional tip provides a soldered, multi-point connection that supports full TriMode measurement capabilities at full probe bandwidth.
If care is taken during the soldering process, this probe tip can be reused through multiple soldering operations. In some applications the
robust mechanical design of the tip and flexible cable construction provides better usability, compared to the lower cost flex circuit tips.
The first time the probe tip is detected, S-parameter data for the probe tip is sent to the oscilloscope, and probe-tip specific DSP filters are
generated.

P77BRWSR

The optional browser connects to the circuit using two input contacts with very fine point tips. These tips have built-in compliance 0.02 in
(0.5 mm) and adjustable spacing 0.008 in to 0.210 in (0.2 mm – 5.3 mm). The input contacts include an embedded damping resistor for
optimum measurement performance.

The browser tip can be held in place or can be used to make hands-free connections to the DUT when using the Browser Tri-Pod
accessory, or a probe positioner, such as the Tektronix PPM203B. The browser includes multiple sets of S-parameters based on the
spacing of the tips. The spacing is monitored and the correct set of S-parameters are automatically used.

P77C292MM adapter

Use the P77C292MM, 2.92 mm adapter to connect a P7700 series probe to a DUT with 50 Ω test point connectors. 2.92 mm connectors
are mechanically compatible with SMA connectors.

Figure 3: P77C292MM adapter

The adapter supports testing of serial standards such as HDMI, MIPI M-PHY, and DisplayPort; cables and retainer are included.

P7700 Series TriMode™ Probes Technical Reference 12

Theory of operation

After connecting the adapter to the flex cable, use the retainer to provide a secure connection to the flex cable to minimize movement or to
attach the adapter to the hand’s free tripod.

For stacking more than one adapter, use the linkage adapter accessories to secure the P77C292MM adapters together.

Probe input architecture

Input architecture

P7700 Series probes feature a new probe architecture that addresses the need for high frequency response with decreased probe loading
for high-speed, low power applications such as MIPI® and LPDDR. High performance probes with multi-GHz bandwidth have evolved
in recent years, starting from traditional designs with metal pin tips attached to a probe head amplifier located at the end of a coaxial
cable. As the probe bandwidth extended to 10 GHz and above, probe designs migrated to connectorized amplifier input structures that
supported a variety of high frequency passive probe tips, including solderable tip designs. These probe tips typically provide a passive
input attenuator network at the probe tip followed by a long cable attached to the probe amplifier connection socket. Although these
passive tip, probe designs enable good, high frequency performance, they show higher probe loading in the frequency band below 1 GHz
than earlier traditional designs with an amplifier closer to the probe tip. A probe with this higher loading characteristic below 1 GHz has
problems when taking measurements of signals such as MIPI that can be switched to an unterminated, high impedance mode for low
power operation. The P7700 Series probe solves this loading problem by introducing an active probe tip design with a tiny buffer amplifier
located near the tip inputs. By locating an amplifier with a high impedance attenuator network at the probe tip inputs, the probe tip parasitic
capacitance can be kept much lower than passive cable tip designs, thus reducing probe loading in the low power signaling frequency
band used by serial data standards such as MIPI.

The following figure shows a simplified diagram of the TekFlex active probe tip architecture.

Figure 4: P7700 Series TriMode probe input architecture

The TekFlex active probe tip has two inputs, A_IN and B_IN, which can, depending on the tip design, support TriMode measurements.
With a TriMode tip, such as a TekFlex solder-in tip, it is possible to make differential, single-ended A, single-ended B, and common-mode
measurements, all from a single soldered differential signal connection to a DUT. The soldered wire connections between the two probe
tip input signal vias and DUT differential signal nodes should be kept as short as possible (as should the ground via connections if
single-ended measurements will be made). The A and B input signals on the probe tip pass to a matched pair of damping resistors, Rd,
that isolate the probe connection to the DUT. The damping resistor value of approximately 100 Ω also serves to tune the probe tip high
frequency response. Following each input damping resistor is a pair of attenuation resistors, Rs and Rp. The attenuation resistor values

P7700 Series TriMode™ Probes Technical Reference 13

Theory of operation

depend on the specific probe tip attenuation factor design. There are currently two attenuation factors available as shown in the following
table with approximate attenuation resistor values. The probe tip attenuation factor in the table includes an additional 2X factor due to
attenuation from the 50 Ω tip buffer output impedance and the 50 Ω probe amplifier termination impedance.

Table 1: Probe tip attenuation factors

Attenuation factor Rs Rp Dynamic range Offset voltage range

4x 25 kΩ 25 kΩ 2.5 V

10x 60 kΩ 15 kΩ 6.0 V

pp

pp

±4.0 V

±10.0 V

The input attenuation resistors serve three major functions for the dual input tip buffer:

• The high resistance of the attenuation resistors provides very light loading on the probe input signals.

• The probe tip attenuation factor expands the linear dynamic range of the probe tip inputs.

• The probe tip attenuation network provides a resistive summing junction for injecting an offset voltage signal to extend the probe tip
operating voltage window.

TekFlex active tips contain a pair of unity gain amplifiers that buffer the DUT differential input signal. These buffer amplifiers provide
an impedance conversion for the input signals from the high impedance input attenuator at the tip input to the 50 Ω output drive at
the tip output. The buffer amplifier 50 Ω output impedance is needed to drive the probe TekFlex connector and meter-long main cable
transmission lines with good high frequency fidelity. The new TekFlex interface to which TekFlex probe tips are attached includes both a
dual high frequency connection for the probe tip signals as well as a low frequency connection for eight messenger wires that provide
power and control for the active probe tips.

The control features of the new TekFlex interface include two analog tip offset voltage signals, a pair of digital communication signals for
accessing the probe tip S-parameter memory, and a probe tip temperature monitor signal.

The probe tip S-parameter memory contains characterization data for use with DSP correction filters that are unique to the probe tip. The
S-parameter memory includes a unique data header used in automatically identifying the probe tip type and serial number. The A and B
signal outputs from the probe tip are connected by high frequency spring contacts in the TekFlex connector to a pair of delay-matched
coaxial cables that carry the input signals through the main cable and into the comp box. These signals terminate to a pair of 50 Ω
termination resistors at the probe amplifier in the comp box. The termination resistors have an adjustable termination voltage connection
for optimal loading of the probe tip output signals. The TekFlex interface messenger wires are routed as a small gauge ribbon cable, along
with the delay-matched coaxial cables, inside a shielded main cable assembly.

The P7700 Series probe amplifier has several cascaded amplifier stages that condition the probe tip differential signal for precision
measurement fidelity. The complex input stage of the probe amplifier selects the desired TriMode input mode.

This input stage of the probe amplifier includes connections for injecting a pair of adjustable probe offset voltages for precision control of
the probe output zero voltage, which is a measure of the output signal with volts at both probe tip inputs.

The next stage in the probe amplifier is the step gain stage. The step gain stage provides several switchable, coarse gain steps, that
extend the sensitivity range of the probe measurement down to the millivolt level with good noise performance. The step gain stage is
automatically switched to its optimum setting by the oscilloscope as the oscilloscope vertical channel sensitivity is adjusted by the user.

The final stage of the probe amplifier is the variable gain stage. The variable gain stage is used for fine tune adjustment of the gain
of the probe and probe tip to its calibrated value. The calibrated gain setting is determined from calibration constants characterized
during manufacturing testing of the probe and probe tip and includes compensation for probe temperature variation. Although the signal
that passes through the probe amplifier is processed as a differential signal through the internal amplifier stages, it is routed to the
oscilloscope’s TekConnect interface as a single-ended output.

The ground path for high frequency signal return currents is shown in the probe architecture figure. (See Figure 4 on page 13.) The probe
ground path is continuous and along the following path:

• Extends from the DUT ground vias connections at the probe tip input

P7700 Series TriMode™ Probes Technical Reference 14

Theory of operation

• Through the probe tip ground path

• Through the TekFlex connector ground spring contacts

• Along the main cable coaxial shields into the probe comp box

• Through the probe amplifier circuit board ground plane inside the probe comp box, and

• Through the TekConnect interface to the host oscilloscope ground

A TriMode tip requires a short DUT ground reference for making low noise single-ended probe measurements.

Although two ground via connections are available on the probe tip input, a single ground via wire connection is usually adequate
for making single-ended measurements of both the A and B input signals or a common-mode measurement, all of which are ground
referenced.

If only one single ended signal will be connected to the probe, the user has the choice of connecting the A input to the signal and the B
input to ground, or connecting the A input to the signal and the ground input of the probe to the ground input of the DUT. In this situation,
Tektronix recommends using A-B mode with the B input connected to ground. Reasons for this recommendation include that with the B
input left disconnected, there is a possibility of an interfering signal coupling into the input of the probe and distorting the measured signal
acquired on the A side.

A second reason for using A-B vs. A-ground is that it is often more convenient to connect the differential inputs of the probe to a device
and keep the wire lengths short. The ground connections of the probe are set back from the tip and may not be as convenient to connect to
a DUT with tightly spaced test points.

The optional accessory P77BRWSR is a variable-spacing probe tip which operates in Differential Input mode only. The P77BRWSR
Browser probe tip does not have a physical ground connection at the probe tip; but the differential measurement process itself provides a
high frequency virtual ground connection between the A and B signal input pins. A low frequency ground connection is optionally available
at a square-pin socket on the browser probe tip housing.

The comp box receives power and control signals from the oscilloscope through the TekConnect interface. The TekConnect interface is
an intelligent probe connection that includes many automated and manual control features. For example, there is a probe S-parameter
memory in the comp box that stores high frequency characterization data for the probe signal path.

The downloaded S-parameter data for a probe and attached probe tip is used by the oscilloscope to generate a DSP correction filter for
optimum measurement fidelity. Because this S-parameter data is unique and serialized for each probe and probe tip, it only needs to be
downloaded once to an oscilloscope.

Automatic probe tip type identification is another example of the intelligent operation of the P7700 Series probes. When no probe tip
is attached to the TekFlex connector of a P7700 Series probe, the TekFlex probe tip interface power is disabled. When a probe tip is
attached to the TekFlex connector, the attachment is detected by the probe and the probe queries the probe tip memory to check for a valid
identification header. If a valid probe tip type is verified by this TekFlex data interface query, the probe tip power is enabled until the probe
tip detachment is detected.

When probe tip power is enabled, an LED is activated on the probe tip, indicating that the TekFlex interface and attached probe tip appear
to be operating properly. If the probe tip type attached to the TekFlex connector is a browser probe tip, the probe tip automatically detects
the current tip spacing and communicates that information to the oscilloscope.

There are several calibrated tip spacing regions defined for the browser tip, which affect the frequency response of the browser tip signal.
Wider tip spacing tends to degrade the browser tip frequency response. The oscilloscope uses the current tip spacing region information to
select the optimum DSP correction filter for use with the browser tip measurements.

Probe input architecture with the P77C292MM SMA adapter

The P77C292MM adapter is a passive probe adapter; there are no active components within the adapter. It is intended to connect the
P7700 series probes to 50 Ω RF test points.

The following figure shows the simplified diagram of the P7700 Series TriMode probe input architecture with the P77C292MM SMA
adapter. Because there are no active components within the adapter the A and B inputs are passed through directly to the probe amplifier.

P7700 Series TriMode™ Probes Technical Reference 15