Electrical Engineering

Internal Gate Resistance Tester

Full vector measurement capability

New version. August 2019

Internal Gate Resistance Tester, DUT Interface

Handler Interface. Analog & Digital boards

VDS-1801 INTERNAL GATE RESISTANCE TESTER  is a vector-based measuring instrument for measuring complex impedanсе. Unlike testers that implement the resonance method of gate resistance measurement, it measures the gate complex impedance, its active part and reactive part.

The VDS-1801 uses a 4-wire circuit to connect the tester to the transistor being measured. Separation of current and voltage electrodes eliminates the lead and contact resistance from the measurement. This is an advantage for precise measurement of low resistance values.

Rg Tester is executed on one printed-circuit board, high degree of integration and represents absolutely independent finished design capable to work both independently, and as a part of measuring complexes. From the measurement process to the output of the finished result - everything is implemented on one board. It is possible to manage and get the finished result with the help of any terminal capable to receive and transfer data on a serial port.

One 6.0" x 4.0" x 0.75" printed circuit board, serial interfaces and a very simple communication protocol allow the tester to be integrated into existing measuring instruments that measure other MOSFET  transistor parameters.

The principle of operation of the instrument was developed in 2006 - 2018. 2007, 2013, 2014.

The RG Tester has basic accuracy of 0.1%.  The RG tester is controlled by a high-speed microcontroller with embedded logic that controls the display, as well as settings measurement conditions and performing calculations. Powerful FPGA device Cyclone III allowed to decrease test time and to use multi test mode. Test time is less than 0.13mS, 10 times faster than RG Tester 2014.

Two signal oscillators 2 MHz and 3.58 MHz. The number of tests have no limitations. To measure impedance from low value to high values, RG tester has a several measurement ranges.



Measured Device

  Single or dual die MOSFET, IGBT


N channel, P channel or combination


Standard Tester /Handler Interface

Sine wave source

  Test frequency  2000 kHz,  3580 kHz

Signal level

Amplitude value max. 2048 mV

   Output impedance


Absolute accuracy, resolution

0.1 ,   0.1 pF,  0.1 nH

Equivalent measurement circuit


Measurement terminals

Four-terminal pair

Test cable length

From 0 to 2m

Test time

0.126 ms x Number of tests + 4ms

Averaging (number of tests)

1 to 999, programmable

Internal gate resistance (Rg)

1 - 1000000.0

Input D.U.T. capacitance

200 - 100000 pF

   Warm - up time

< 4 minutes


µLCD - 35DT

Capable of displaying

Measured values, control settings


Open, short, load

Contact check resolution



Functional, open/short, contact check

Test operation

Auto or manual


USB/RS232, RS232, IGBT(optional)



Compare table













Measurement Method


I-V Measurement

Measurement Terminal



Sine wave source




0.365 kHz




1 Hz

Source Voltage









Source Current









Internal resistor Rg






0.1 mΩ

Internal capacitor Cg








0.1 pF

Test Time









3041-R, Source Current, Unit - mA


Circuit description

The tester works on any of two frequencies - 2 MHz or 3.58 MHz. Generators are made on JFET transistors  with quartz frequency stabilization.  The use of an amplifier with very low distortion and a quartz filter with a bandwidth of 400 Hz allowed to obtain a peak value of the signal equal to 2000 mV at the level of harmonics -70 dbc. The output impedance of the amplifier is 50 Ohm.

The VDS-1801 uses a 4-wire circuit to connect the tester to the transistor being measured. The shielded four-terminal configuration can reduce the effects of lead impedance because the signal current path and voltage sensing cables are independent. Accuracy for the lower impedance measurement range is improved typically down to 1 mΩ.

A pair of contacts that is designed to connect a force-and-sense pair to a single terminal or lead simultaneously is called a Kelvin contact.

The principle of the tester is very simple - we measure the value of current and voltage and determine the phase shift between current and voltage. We define the components of the complex resistance, the active part, which is the internal gate resistance, and the reactive part, which in the case of MOSFET transistor determines the capacity of the junction

To measure current and voltage, 16-bit PulSAR ADC are used. Drivers of analog-to-digital converters ADC, are made on differential amplifiers.  LVDS buses are used for digital control and data transmission circuits. All the necessary mathematical operations are performed in the hardware, which allows you to achieve the highest possible speed, which can not even be theoretically higher. Processing of actual and imaginary parts of current and voltage signals takes place in four channels simultaneously and in parallel

Reading the results, averaging, slightly compensating for the effects of parasitic capacitors, inductances, starting tests and calibrations, and controlling and calibrating the generators is carried out by the NIOS II microcontroller. The 32-bit controller is formed in the same FPGA.

The processing of the current and voltage measurement results passes in parallel along four channels, in the 32-bit floating point format. The final processing of the results occurs in a 32-bit embedded-processor Nios II, formed in FPGA.

The results of measurements are influenced by the temperature of the elements on the board. To stabilize the temperature on the board, a digital temperature sensor is installed, which is used in the thermostat mode and controls the fan.The temperature of the board is maintained with an accuracy of 0.0625°C.

The measurement results are fully dependent on the quality of the clock and the ability to accurately set frequency and phase. The clock oscillator is made on the chip Si570  from Silicon labs. The oscillator has a very low level of phase noise and excellent frequency stability. A special circuit generates a clock for the ADC channels of current and voltage and allows you to set the clock frequency of the generator with an accuracy of 1.25 Hz and the phase of one channel relative to another with an accuracy of less than 0.005 °.

The configuration data, calibration and original individual board data are stored in the EEPROM.

 The required voltages for supply from an external power source are + 8V (400mA), -8V (200mA), + 5V (300mA).


Mesurement method

In order to understand the implications of aliasing in both the time and frequency domain/ first consider the case of a time domain representation of a single tone sinewave sampled as shown. In this example, the sampling frequency fs is not at least 2fa, but only slightly more than the analog input frequency fa - the Nyquist criteria is violated. Notice that the pattern of the actual sample produces an aliased sinewave at a lower frequency equal to fs - fa.

This is similar to the analog mixing process and implies that somefiltering ahead of the ADC is required to remove frequency components which are outside the Nyquist bandwidth, but whose aliased components fall inside it. The filter performance will depend on how close the out-of-band signal is to fs/2 and amount of attenuation required.

All mathematical calculations in the measurement process are done in hardware. The measurement data are processed and calculated simultaneously in four channels. The results of the test are submitted for further processing to the integrated NIOS II processor, in which they are averaged, corrected and transmitted via the serial port to the computer.

Theory of operation.

The RG Tester uses technique to measure unknown impedance by measuring the voltage across the device under test (DUT) and the current through it.

The output of a signal source is applied through a source resistor Rs to the unknown device Zx and range resistor Rr. The effect of convertor I/U is to cause the same current Ir that flows through the unknown device to flow through Rr, and, as a result, to drive the junction of the unknown device and Rr to zero volt (virtual ground). Across Rr there is a voltage Vx = Ir × Rr. Voltages across the unknown device and across Rr, respectively, are connected to a differential amplifiers.

Measurements are performed using an  16 bits A/D converter that is read by the controller.

The complex ratio of voltage to current is equal to the complex impedance. The measured complex impedance is corrected by calibration factors, for both absolute value and phase. The other parameters, such as L, C, R, Q, D, are derived mathematically from the corrected impedance value, with the model and the test frequency chosen by the user.

All mathematical calculations in the measurement process are done in hardware. The measurement data are processed and calculated simultaneously in four channels, in the 32-bit floating point format. The results of the test are submitted for further processing to the  32 -bit embedded - processor NIOS II, formed in FPGA,  in which they are averaged, corrected and transmitted via the serial port to the computer.


All devices are enclosed in the same type of Split Body Aluminum Enclosures and differ in size. All openings are made on a CNC milling machine. The inscriptions are made by mechanical engraving on the same equipment. Powder coating.

Split Body Aluminum Enclosure. 8.5" L x 6.144" W x 3.090" H

 4-wire (Kelvin sensing) fixture

 Split Body Aluminum Enclosure w/ Plain End Plates 4.0"L X 2.610"W X 1.160"H

         DUT Interface has been developed for comfortable work with the tester. On the top panel there is a mode switch: OPEN, SHORT D-S, LOAD. Socket of 3M company (factory part number 203-2737-55-1102, Digi-Key part number 3M10849-ND).

         Inside the box there is a calibration element for LOAD calibration in SINGLE MODE and two elements for the same calibration in HANDLER mode. In the OPEN position, the socket is connected to the cables. In the SHORT D-S position, the socket is connected in the same way as in the OPEN position, but the DRAIN and SOURCE contacts are shortened by a switch. In the LOAD position, a calibration device for Load Calibration is connected to the cables.


4-wire (Kelvin sensing) handler interface

Split Body Aluminum Enclosure w/ Flanged End Plates 2.75" L x 3.12" W x 1.852" H

         In order to ensure accurate measurements, Rg Tester cable-connected to a remote pod ( Handler Interface ) that is located as close as practical to the handler.

With Handler Interface tester is equipped with CONTACT CHECK and OPEN/SHORT test functions, and performs high volume production testing.

         A special interface has been developed for working with handler. Structurally it is made by the separate block. If, in the case of device measurement in a laboratory environment where contact quality is easily monitored and contact resistance measurement is not necessary, it is important to monitor contact resistance and condition in conjunction with handler for timely maintenance and replacement.

         This project uses a completely different idea.The contact resistance is measured by the tester as well as the gate resistance of the MOSFET transistor. The result is the value of the complex contact resistance. The measurement results are compared with the values recorded in the EEPROM during calibration, and the difference is displayed in a file along with the values of resistance and reactivity of the shutter. In this way, the physical condition of the contacts can be monitored and maintenance measures can be taken in a timely manner.

         The device uses  relays Coto 9117, G6K_2P,  the control circuit is implemented on the microcontroller PIC24. The contact resistance measurements are performed at the operating frequency of the tester in the same way as the gate resistance measurements.

         HANDLER INTERFACE is designed to measure the parameters of two devices.  The interface is connected to the tester via RS232 serial interface. This cable is used to supply +8V, -8V power.


Handler interface. Analog board.

Handler interface. Digital board.

         Analog board - analog switch, made on reed relays Coto 9117 and Signal Relays G6K-2P.  Each relay of the interface has a LED, which clearly shows the status of the relay.

The digital part is two interfaces. RS232 for communication with the tester and ATE for communication with the handler. The interface with the handler is galvanically isolated and powered by a DC/DC converter. The interface core is the PIC24 microcontroller.

There are two crystal oscillators on board, nterfaces: USB/COM, RS232, COM 3.3V, COM 5V, General I/O - 13, fan control.

PCB, Top view

The printed circuit board of the tester has all the necessary power supplies. + 7VA, + 5VA, -5VA, -2.5VA, + 3.3VA, + 3.3VD, + 2.5VD, + 1.2VD. The required voltages for supply from an external power source are + 8V (400mA), -8V (200mA), + 5V (300mA).

PCB, Bottom view

RG Tester Power supply  + 8VA, -8VA, + 5VD.

Voltage regulators +8VA and -8VA - adjustable.

Assembled power supply board

3.5" TFT Intelligent Display Module from 4D System. If desired, the test can be operated without a personal computer, it is enough to connect the Resistive Touch display.

3.5" TFT Intelligent Display

User interface

For this version of the tester, a program is written for controlling and processing the measurement results. The program allows you to calibrate, test, set parameters and test conditions, create and store logs.

The RG Tester Control program is written in C # in Microsoft Visual Studio. Works under any Windows OS from Xp to Windows 10. Controls calibration, testing, settings, communication, savings test's results.

RG Tester Control software. Testing tab.. Screen shot

Testing tab.   500 tests per 59mS. Jumping 0.3 mΩ = 0.03%

In the terminal window displays all information on the data exchange. All data is in ASCII format.

 In addition to the basic commands, some functions of the tester that are not associated with the control buttons can be controlled through the terminal.

The format of the tester commands is very simple. All commands consist of two letters, a colon and data separated by commas.

Terminal Tab

The new version allows you to get the values of R, C, L. Measurements are made at two frequencies, the test time is doubled, but allows you to get the exact values. I don't know about the same R, L, C meters.

When measuring, you can choose between 2 MHz and 3.6 MHz or two frequency measurement. Works for both Single DUT and Handler.


Setting the thermostat temperature, calibration accuracy, calibration samples value and number of tests in one package.

Settings details are stored in an EEPROM (electrically erasable programmable read-only memory).

Settings tab

The objective of component measurement is to accurately determine the real value of a component including parasitic. In order to know the real values of the DUT's, we need to minimize the measurement errors by using proper measurement techniques.

Calibration tab

Parameter editor of transistors, working with lists, setting lower and upper limit values. Selection of measured parameters.

Task Editor tab

The main purpose of the panel is to display generalized test results. In the upper part of the panel there are several interface elements, which are available to the operator and allow you to enter data for the identification of tests.

Data Logger tab

The panel is designed to work with handler interface in manual mode. From the panel it is very convenient to test the equipment, handler contacts, check the devices for functioning, i.e. whether there is an open or closed circuit.

Test Result tab

If there are any questions or wishes

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The video was created in real time and was not edited.

Warming, logging, settings, testing


Calibration. Short, open, load, clock.

Downloads, Links

Keysight Technologies   Impedance Measurement Handbook


© V.Dmitriyev 2018