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CT4121
User Manual
1 MΩ // 3 pF
1.2 GHz Active FET Probe
10:1 with 50 Ω Termination
POWER
LED
1.2 GHz 10:1 1 MΩ // 3 pF 40 V
pk
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Safety Summary
To avoid personal injury and/or product damage, review and comply
with the following safety precautions. These precautions apply to both
operating and maintenance personnel and must be followed during all
phases of operation, service, and repair of this probe.
A
WARNING statement calls attention to an operating procedure,
practice, or condition, which, if not followed correctly, could result in
injury or death to personnel.
A
CAUTION statement calls attention to an operating procedure,
practice, or condition, which, if not followed correctly, could result in
damage to or destruction of parts or the entire product.
Inspect the Probe
Inspect the probe and accessories for cracks and frayed or broken
leads before each use. If defects or damages are noted, DO NOT USE
the probe.
Handle Carefully
Handle the probe with care to avoid injury, especially when tted with
sharp tips.
Dry Conditions
Hands, shoes, oor and work bench must be dry. Avoid making
measurements under humidity, dampness or other environmental
conditions that might affect safety.
Do Not Remove Probe Housing
Removal of the probe’s housing may expose you to electric shock.
If necessary, disconnect the inputs and outputs of the probe before
opening the case.
Hazardous Contact
To avoid injury, remove jewelry such as rings, watches, and other
metallic objects. Do not touch exposed connections and components
when power is present.
Unexpected Charges
Hazardous voltages may be present in unexpected locations in circuitry
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being tested when a fault condition in the circuit exists. Capacitors
inside the instrument may retain a charge even if the instrument is
disconnected from its source of supply.
Grounded Instruments
Use only grounded instruments. Do not connect the probe’s ground
lead to a potential other than earth ground. Always make sure the
probe and the instrument are grounded properly.
Use Only in Ofce-Type Indoor Setting
The probe is designed to be used in ofce-type indoor environments.
Do not operate the probe:
z In the presence of noxious, corrosive, or flammable fumes,
gases, vapors, chemicals, or finely-divided particulates.
z In environments where there is a danger of any liquid being
spilled on the probe.
z In air temperatures exceeding the specified operating
temperatures.
z In atmospheric pressures outside the specified altitude limits or
where the surrounding gas is not air.
Not for Critical Applications
This probe is not authorized for use in contact with the human body or
for use as a component in a life-support device or system.
Do Not Substitute Parts
Do not install substitute parts or perform any unauthorized modication
to the instrument.
Only Qualied Personnel
This probe should only be used by personnel who are trained,
experienced, or otherwise qualied to recognize hazardous situations
and who understand the safety precautions necessary to avoid
possible injury when using such a probe.
Observe Maximum Working Voltage
Do not use the CT4121 above 40 V (DC + AC peak) CAT I between
each input lead and earth.
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Use Proper Power Source
Do not operate this probe from a power source that applies more than
the voltage speci ed.
Compliance Statements
Disposal of Old Electrical & Electronic Equipment
(Applicable in the European Union and other European
countries with separate collection systems). This product
is subject to Directive 2012/19/EU of the European
Parliament and the Council of the European Union on
waste electrical and electronic equipment (WEEE), and in
jurisdictions adopting that Directive, is marked as being
put on the market after August 13, 2005, and should not
be disposed of as unsorted municipal waste. Please
utilize your local WEEE collection facilities in the
disposition of this product and otherwise observe all applicable
requirements.
This probe is in compliance with IEC-61010-031 CAT I, Pollution
Degree 2.
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1 Introduction
Overview
The CT4121 is a compact FET probe with very high input resistance
and low input capacitance. With a 1.2 GHz bandwidth, this probe is
ideal for timing analysis or troubleshooting high speed logic circuits,
for design verication of disk drives, as well as for wireless and data
communication design. The CT4121 can measure up to ±40 V (DC +
AC peak). Compatible with oscilloscopes from all major manufacturers,
the probe is powered by the included 9 V battery or direct from the
oscilloscope using the included USB power lead.
Features:
z 1.2 GHz bandwidth (-3 dB)
z Up to ±40 V (DC + AC peak)
z Attenuation 10x
z High accuracy (±2%)
z Power indicator LED
z SMD accessory kit
Initial Inspection
This probe is tested prior to shipment therefore it is ready for
immediate use upon receipt. An initial physical inspection should be
made to ensure that no damage has been sustained during shipment.
After the inspection, verify the contents of the shipment.
Kit Contents:
z Active FET probe
z 50 Ω feed-through terminator (CT2944-50)
z USB power lead (CT4122)
z 9 V battery
z Offset adjustment tool
z User manual
z SMD kit
• (2) SMD test clip, gray (CT3659-8)
• (2) MicroLeads, 0.8 mm, Pin-Jack, 5 cm, Black/Red
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• (2) MicroLeads, 0.8 mm, Pin-Jack, 10 cm, Black/Red
• (4) Ground pin, bent
• (6) Test tip, uninsulated, 0.8 mm x 11.6 mm
2 Product Overview
CT4121 Description
Offset Adjust
Linear Range @ 10:1
Absolute Max Range
±15 V DC+peakAC
±40 V DC+peakAC
CT4121 Active FET Probe
POWER
LED
1.2 GHz 10:1 1 MΩ // 3 pF 40 Vpk
BNC Output
Connector
Power Switch
54 cm Lead
50 cm Lead
Oset Adjustment
Hole
Input Pins Power
Indicator
Power Box
Figure 1 Front Panel Diagram CT4121
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3 Using the Probe
Power Connection
Slide open the battery compartment and attach a 9 V battery to the
snap connector. Place the battery inside compartment and then slide
the cover back in place. See Figure 2.
Figure 2 Battery Connection
Alternatively, connect the 9 VDC power lead to the power jack on the
probe. See Figure 3. Connect the lead to a USB power source.
POWER
LED
CT4121 Active FET Probe
1.2 GHz 10:1 1 MΩ // 3 pF 40 Vpk
Power
Jack
Figure 3 Power Jack
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WARNING
At the time of powering on the probe, the input leads must not be
connected to an item to be tested. Never operate the probe with the
case open.
Inspection Procedure
1. Connect the BNC output connector to the vertical input of the
oscilloscope.
2. Power on the probe.
3. Set the attenuation setting on the oscilloscope to match the
probe (10x).
4. Set the oscilloscope input to DC coupling and .5V/div. Center
the trace on the display.
5. Connect the input pins of probe to a function generator and
select a square-wave output of 10 V amplitude and 100 kHz
frequency.
6. A 100 kHz square-wave of 1V amplitude will be displayed on the
screen of the oscilloscope. This indicates the probe is working
properly.
Getting Started
1. Attach the desired SMD accessories to the inputs
2. Connect the BNC output connector to the vertical input of the
oscilloscope.
3. Power on the probe.
4. Set the attenuation setting on the oscilloscope to match the
probe (10x).
5. Connect the inputs to the circuit to be tested.
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Vertical Scale on Oscilloscope
The actual vertical scale of the oscilloscope is equal to the attenuation
factor (10x) multiplied by the range of vertical scale selected on the
oscilloscope. For example, with the oscilloscope on 2.0 V/div, the
real vertical scale is 10 x 2.0 = 20 V/div. This value applies when the
oscilloscope is set to a 50 Ω input impedance input. If the oscilloscope
is set to the typical 1 MΩ, the actual vertical scale will be cut in half to
10 V/div. See Table 1.
Vertical Scale on Oscilloscope
Scope Input
Impedance
Probe
Attenuation
Setting
Actual
Attenuation
Setting
Vertical Scale
Reading on the
Oscilloscope
Actual Vertical
Scale of the
Oscilloscope
50 Ω 10x 10x 2.0 V/div 20 V/div
1 MΩ 10x 5x 2.0 V/div 10 V/div
Table 1 Oscilloscope Readings
4 Cleaning
This probe does not require any particular cleaning. If necessary, clean
the case with a cloth slightly moistened with soapy water. Make sure
the probe is completely dry before reconnecting it to an oscilloscope.
WARNING
Dry the probe thoroughly before attempting to make voltage
measurements.
CAUTION
Do not subject the probe to solvents or solvent fumes as these can
cause deterioration of the probe body and cables.
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5 Specications
All specications apply to the unit after a temperature stabilization time
of 20 minutes over an ambient temperature range of 25 °C ± 5 °C.
Electrical Specifications
Parameter Characteristics
Bandwidth (-3dB) 1.2 GHz
Rise Time (probe only) 291 ps
Attenuation ratio 10x
Accuracy ±2%
Input Dynamic Range
(DC + AC peak)
±15 V
Maximum Input Voltage
(DC + AC peak)
±40 V
Input Impedance 1 MΩ // 3 pF typical
Output Voltage Swing ±1.5 V (driving 50 Ω oscilloscope input)
Offset (typical) ±5 mV
Adjustable output offset range ±28 mV
Noise (typical) 0.3 mVrms
Source Impedance 50 Ω
Power Supply
9 V battery (included) or
CT4122 USB power lead (included) or
CT3723 power adapter (optional)
Safety Specications IEC 61010-031 CAT I
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Mechanical Characteristics
Parameter Characteristics
Weight 200 g
Dimensions 83 x 19 x 14 mm
Cable Length 120 cm (Total)
Environmental Characteristics
Parameter Characteristics
Operating Temp/Humidity -10°C to 40°C / Up to 85% RH
Storage Temp/Humidity -30°C to 70°C / Up to 85% RH
Pollution Degree Pollution Degree 2
Altitude
Operating: 3,000 m
Nonoperating: 15,300 m
Specications are subject to change without notice. To ensure the most
current version of this manual, please download the current version
from our website: caltestelectronics.com
Performance Data Plots
10
8
10
9
Figure 4 Maximum Input Voltage Derating Curve
1
10
100
Voltage (V)
(DC + ACpeak)
10
7
10
6
10
5
Frequency (Hz)
Maximum Input Voltage Derating Curve
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Figure 5 Frequency Response of CT4121
Frequency Response
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10
9
Input Impedance (Ohm)
10
7
10
6
10
5
10
4
10
3
10
2
10
1
10
1
10
2
10
3
10
4
10
5
10
6
10
7
10
8
1
Frequency (Hz)
Black - Measured by LCR meter
Grey - Simulated by Altium software
Figure 6 Input Impedance vs Frequency Data Graph
Input Impedance vs Frequency Data Graph
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6 Service & Warranty Information
Limited One-Year Warranty
Cal Test Electronics warrants this product to be free from defective
material or workmanship for a period of 1 year from the date of original
purchase. Under this warranty, Cal Test Electronics is limited to
repairing the defective device when returned to the factory, shipping
charges prepaid, within the warranty period.
Units returned to Cal Test Electronics that have been subject to abuse,
misuse, damage or accident, or have been connected, installed or
adjusted contrary to the instructions furnished by Cal Test Electronics,
or that have been repaired by unauthorized persons, will not be
covered by this warranty.
Cal Test Electronics reserves the right to discontinue models, change
specications, price, or design of this device at any time without notice
and without incurring any obligation whatsoever.
The purchaser agrees to assume all liabilities for any damages and/or
bodily injury which may result from the use or misuse of this device by
the purchaser, his employees, or agents.
This warranty is in lieu of all other representations or warranties
expressed or implied and no agent or representative of Cal Test
Electronics is authorized to assume any other obligation in connection
with the sale and purchase of this device.
Service
If you have a need for calibration or repair services, technical or sales
support, please contact us:
22820 Savi Ranch Parkway
Yorba Linda, CA 92887
800-572-1028 or 714-221-9330
caltestelectronics.com
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Notes
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© 2017 Cal Test Electronics450830-001 Rev. A
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