Syscomp CTR-201 User Manual
Syscomp Computer Controlled Instruments
CTR-201 Curve Tracer
Syscomp Electronic Design Limited
http:\\www.syscompdesign.com
Revision: 2.1
November 2017
Revision History
Version Date Notes
1.00 November 2014 First revision
1.10 April 2015 Feature Update
1.11 March 2016 Solar cell option added
2.1 November 2017 New software and hardware
Contents
1 Introduction 1
2 The CTR-201 Curve Tracer 2
3 Measurements 4
3.1 Device Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2 Instrument Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.3 Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.4 Zener Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.5 NPN Transistor (BJT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.6 PNP Transistor (BJT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.7 N-Channel MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.8 P-Channel MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.9 N-Channel JFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.10 Gene ral 2-Terminal Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.10.1 2-Terminal Measurement, Voltage Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.10.2 2-Terminal Measurement, Curren t Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.11 Small Signal Transistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.12 Solar Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.13 Lam bda Diode, Negative Resistance Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.14 Vacuum Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4 How It Works 16
5 Calibration 21
6 Installing the Software 23
6.1 Packaged Executable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.2 Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.2.1 Obtaining the Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.2.2 Installing the Tcl Interpreter on a Windows Machine . . . . . . . . . . . . . . . . . . . . 24
6.2.3 Executing the Sou rce Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7 Commands 24
7.1 Testing the Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
7.2 Command List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
7.3 Export and Import Data, Compare Measurements . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.4 48 Volt Power Enable/Disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.5 Pulsed VI Measureme nt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
i
List of Figures
1 VI Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Typical Control Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Cursors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4 Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5 1N3022 Zener Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6 NPN Transistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7 PNP Transistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8 N-Channel MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9 P-Channel MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10 N Channel JFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
11 2-Terminal Measurement, Voltage Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
12 2-Terminal Measurement, Current Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
13 2N4401 NPN BJT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
14 2N4403 PNP BJT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
15 2N7000 N-Channel MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7
16 Solar Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
17 Lambda Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
18 Lambda Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
19 Vaccum Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
20 Curve Tracer Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
21 Attaching to the Ground Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
22 Calibration Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
23 BJT Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
24 48V Power Enable/Disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
ii
1 Introduction
Electronic devices are useful because they cause a specific relationship between voltage and current. A curve
tracer displays the VI c haracteristic of these devices, leading to better understanding of their operation.
(a) Resistor, 1kΩ (b) Diode, MR851
Figure 1: VI Characteristics
As a very simple example, it’s possible to plot the VI characteristic of a resistor on a curve tracer. A resistor
plot appears as a diagonal straight line (figure 1a), the slope inversely proportional to the resistance. There are
simpler and less expensive ways of measuring resistance, but it’s useful to keep that example in mind when
viewing a VI plot.
For example, a diode allows current to flow in the forward directio n, and blocks it in the r everse direction.
As well, there is a small voltage drop across the diode when it is conducting. This voltage drop increases with
current, so th a t the voltage is a non-linear function of the current. We refer to the graph of this function as the
VI Characteristic for the forward-biased diode. Different diodes have different shaped curves. For example, the
voltage drop across a germanium diode is about 0.3 volts. Across an LED, it is 2 or 3 volts. Figure 1b shows the
VI characteristic of a 3 amp silicon power diode.
The curve tracer can also plot a family of VI Curves for NPN and PNP transistors, MOSFETs, JFETs and
many other semiconducto r devices.
Applications of a curve tracer include the following:
Education: Viewing Device Characteristics A lab exercise to measure device characteristics - such as the col-
lector curves of a transistor - helps students to retain important information about devices. It also teaches
students how to interpret the curves to determine device parameters and models.
Modelling a Device Detailed knowledge of the characteristics of a device allows one to model it for a simulation
program. For example , the characteristic of the diode in figure 1(b) can be modelled by an ideal diode in
series with a pure voltage source and resistor. The voltage source models the threshold voltage of the diode.
The resistor models the linear portion of the curve at higher currents.
Measuring the Range of a Parameter A device data sheet generally specifies the behaviour of the device under
certain conditions. The curve tracer can deter mine the behaviour under a range of o ther conditions. For
example, the datasheet of a transistor may not show its incremental collector resistance. This is readily
determined from a curve tracer plot.
1
Testing a device t o determine if it is Functional It can be useful not only to know whether a device is func-
tional, but if it has failed, whether it is a short circuit, open circuit, or some other state.
Testing a device t o determine it meets its Specificat ions One can quickly determine whethe r a device mee ts
certain performance requirements, such as cur rent gain.
Matching Devices by Comparison In certain specialized applications it is useful to be able to match device
characteristics. For example, one wishes to use a pair of matched JFETs for the input to a low-noise
differential amplifier. The two JFETs should be matched, but a matched pair are not available commercially.
For low volume production or a one-off scientific instrument, a group of single JFETs can be sorted and
matched according to their curve-tracer measurements, and then used in pairs.
Testing a Two-Terminal Circuit Two terminal circuits, such as a constant current or constant voltage device,
can be constructed from co mponent parts. The curve tracer is ideal for measuring the properties of these
circuits. As another example, a negative resistance device (Lambda Diode) can be synthesized using two
junction FETs. The curve tracer can b e used to plot its VI characteristic.
Testing Unknown Device If you obtained a large quantity of a particular tra nsistor, it would be possible to de-
termine its princip al characteristics, such as polarity (NPN or PNP) and current gain.
Why do we need a curve tracer to determine device characteristics? Isn’t the information
in the datasheet?
The data sheet for a sem iconductor device will specify some or all of the maximum, minimum an d typical values
for some parameter. For example, the forward voltage drop of a diode will be specified a t some value of forward
current. The datasheet may also show a typical curve of forward voltage vs current. However, in the process of
electronic design and troubleshooting it’s often important to be able the exact behaviour of a given device.
For example, the forward voltage of a silicon diode is often quoted a 0.6 volts. A curve tracer shows that the
forward voltage of an MR851 diode, when conducting 1 amp of cu rrent, is actually about 1.4 volts. This would
be important to know when designing a power supply1.
2 The CTR-201 Curve Tracer
Early examples of the curve tracer instrument generally included a cathode ray disp la y, much like an oscilloscope.
AC line-operated power supplies swept the device voltages and currents, typically at a rate of 60 or 120Hz. The
instrument had many manual controls and extensive analog circuitry. These instruments were excellent for their
time, but they were large, heavy a nd expensive.
The CTR-201 system uses a completely different approach. The test hardware connects to a personal computer
via USB, and the computer runs a control program to operate this hardware. The hardware unit con tains various
controlable voltage and current so urces that actuate the device under test while measuring the voltages and currents
in the device. The measurement results are then handed back to the host PC for display, manipulation, or storage.
There are many advantages to this approach:
• The hardware can be rela tively simple, which reduces its size and cost. Where an electronics lab could
perhaps have one curve tracer that was shared by all staff or students, it is now feasible for each work
station to do its own dedicated measurements.
• The measurement algorithms are defined in software, so the capabilities of the instrument can be modified
and extended.
1
The curve tracer measures the characteristics of a specific device. For a production design where many units are to be produced, one
should use the worst case parameters of a semiconductor in the design. So you should in general not read the measurements from a curve
tracer of one particular device and use those results directly in a design. But you could use the curve tracer to ensure that a given device meets
or exceeds its datasheet specifications.
2
• Measurements are conducted in pulsed mode. Tha t is, the measurement conditions are applied to the device
under test for a brief interval. The hardware captures the device behaviour during the measure ment interval.
The measurement conditions are then removed, allowing the device and the driver electronics to cool. This
approach minimizes the size and cost of the hardware, and allows measurements of a semiconductor device
up to and beyond its rated values.
For example, light emitting diodes are often operated in pulsed mode at peak currents well in excess of their
maximum allowable continuous current. The CTR-201 can take pulsed measurements up to a maximum of
1 ampere forward current.
The interval between me asurements automatically increases at higher currents to control the power dissipation in the device.
• Legacy instruments provided a repeditive display of the measurement curve. In the CTR-201, data is
captured in one measurement sweep, minimizing the dissipation in the device under test.
• Legacy instruments often used dissipation limiting resistors in series with the device under test. Then, as
the current was increased in the device, the voltage across the device decreased. This was a useful approach
to protect the device under test2. However, it limited the me a surement at the corner values of voltage and
current. You could measure the device at maximum voltage or current, but not both at once.
The CTR-201 contains no dissipation limiting resistances, and the current sensing resistances are small. As
a result, the device can be tested at the full limit of the cu rve tracer capabilities - about 35 volts at 1 ampere.
• Legacy instruments typically provide voltage-cur rent curves. A comp uter-based instrument like the CTR201 can provide many more modes of display and analysis, such as the variation in current gain of a BJT
over a range of operating currents, or the incremental collector resistance as a function of collector voltage.
The data can be captured and transferred to a spreadsheet or other prog ram for further analysis.
• Because the CTR-201 hardware is hosted by a computer it is straightforward to capture screen shots, save
the data to a file for further analysis, or project the screen image in a teaching environment.
2
As well, the voltage across the dissipation resistance could be used as a measurement of the current through the device.
3
3 Measurements
3.1 Device Connections
3.2 Instrument Overview
A typical control panel configuration is shown in figure 2. Some sections of this display change according to
the type of device under measurement.
Here we list the various functions on the contr ol panel of the Curve Tracer. These are the functions that apply
to all measure ments.
Menu Bar: File
Save Preset Saves the current control settings.
Load Preset Loads the previously saved contr ol settings.
Menu Bar: View
Trace Smoothing Enable and disable dot connection algorithm that smooths the trace. Disable to see the actual
measurement points.
Figure 2: Typical Control Panel
4
Menu Bar: Tools
Calibration Provides access to the calibration facility of the curve tracer. You will need multiple digital volt-
meters and ammeters to complete this process. Extreme caution is r equired.
Menu Bar: Data
Save, load and clear reference trace. This allows saving and displaying a trac e for com parison purposes.
Menu Bar: Hardware
Connect Provides access to the routine for connecting to a USB port on the host computer.
Pulsed VI Measurements When enabled, the measurements include a ’cooling’ period between each measure-
ment to minimize dissipation in the device under test.
Menu Bar: Help
Manual Accesses this doc ument.
Change Log Accesses the software changes with this version of the software.
About States the version number of the software.
Firmware Upgrade The firmware is the code installed in the hardware unit. It is not the computer code that runs
on the host computer. Forces an upgrade to the firmware. Do not access this unless a firmware upgrade is
essential. An internet connection is required of the host computer.
Check for firmware upgrades on startup Recommended to leave this enabled. To upgrade the firmware, an
internet connection is required of the host computer.
Device Status
Temperature Shows the internal temperatu re of the instrument.
USB Voltage Displays the voltage supplied by the USB connection. Should be ar ound 5 volts.
Input Voltage When taking a measurement, shows the supply voltage from the AC adaptor. Should be around
48 volts.
Device Safety
These controls allow the operator to set the current limit or the power limit for the device under measurement. If
the instrument tries to exceed this value, it stops mea surement and post a warning message.
Current Range
Allows selection of the current measurement range. There are four settings: Auto, 1 amp, 30mA, 1mA. If you
select Auto, the instrument will try to select the optimal measurement range. There will be seen a small glitch in
the trace when switching between ranges. Also, Auto can fail under certain situations, in which case a manually
selected range is necessary.
Select Device
Allows selection of the type of device under measurement. These selections can be used for other purposes as
well. For example, the N-Cha nnel JFET setting has also been used for measuring MESFETs and Russian Vacuum
tubes.
5
Voltage-Mode, Current Mode
The VI measurement setting allows one to set the measurement mode. In Voltage mode, the instrument adjusts
the terminal voltage and measures the current. In current m ode, the instrument adjusts the current and measures
voltage. For example, in a diode-like device, when measured by voltage mode the current increases very rapidly
after the device threshold is reached. It’s much more controllable to operate the in current mode, ie, adjust the
measurement current and report the device voltage
Control Settings
These entry boxes set the parameters for a measurement. Move the cursor to the entry box a nd left click to place
the cursor in the entr y box. Then edit the value. Carriage return is not required. When you click on START,
the instrument software will read the values in these boxes. Usually some experimentation is required to get the
desired curve.
Curve Data
This section of the control panel logs the measured values as they are completed. The ’Save CSV’ function (see
above) copies this data to a .CSV file.
Measurement Cursors
A left click in the plot area deposits a measurement point and shows the coordinates of that point.
A second left click deposits a second point, whic h shows the coordinates of that point. The second point also
generates a line between the two points, a readout of the slope, and a reado ut of the inverse of the slope. This
provides a semi-automatic method of determining incremental conductance and resistance.
For example, in figure 3 the operator has deposited two measurement points on one of the collector characteristic curves. The collector incremental resistance is 420 ohms. This is useful infor mation for building a model of
the transistor for circuit analysis or simulation.
Figure 3: Cursors
6
3.3 Diode
The control settings for a typical diode measurement, and the results of that measurement, are shown in figure 4.
(a) Control Settings (b) Result
Figure 4: Diode
A diode VI characteristic could be measured by placing a voltage between its terminals and measuring the
current (voltage-driven), or passing a current through it and measuring the terminal voltage (current-driven).
Either one will work, but current incr eases very rapidly with voltage once the voltage exceeds the threshold for a
diode. Conversely, forward voltage increases very slowly with cu rrent, so a current-driven measurement is more
controllable and precise.
The current source/sink is available at the centre (Blue) terminal. For the Diode measurement, the software
selects sourcing of current from that terminal. The left (Red) terminal acts as a constant voltage so urce for return
for the cur rent.
3.4 Zener Diode
The zener diode should be measured using the Diode measurement con figuration, which is current-controlled.
Figure 5 shows the characteristics of a 1N3022 zener diode. Figur e 5(a) is the forward characteristic, which
is similar to the forward characteristic of any silicon diode.
Figure 5(b) shows the reverse characteristic. The inverse of the slope of this ch aracteristic is the zener incremental resistance. The 1N3022 is billed as a 12 volt zener. The measurement shows it is more like 10 volts,
highlighing the importance of a curve tracer measurement to verify a device characteristic.
7
Loading...