Electrical Engineering

Internal Gate Resistance Tester

Full vector measurement capability

Internal Gate Resistance Tester, DUT Interface

Handler Interface. Analog & Digital boards

Internal Gate Resistance Tester (RG Tester) is a multi-frequency impedance measuring instrument capable of measuring resistance, capacitance, inductance from 0.1 mΩ to 2000 Ω. Series equivalent measurement circuit.

Ability to work independently, as well as part of the system. The size of the PCB assembly is 6.0 "x 4.0" x 0.75". The small size and well-designed interface allows integrating the tester board into existing measuring systems.

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.

The version of 2016 is developed taking into account the identified shortcomings in previous versions of the project. Fixed firmware errors that significantly influenced the measurement results. Fixed errors in the circuit and PCB.


Figure 1

Circuit description

Analog part of the tester is made on high quality parts from Analog Devices. Amplifiers ADA4899, differential amplifiers ADA4938-1, 16 Bits PulSAR Differential ADC AD7626. The digital part is made on FPGA EP3C40Q240C8N. The use of FPGA has significantly increased the speed of processing the measurement results, will increase the accuracy and stability.

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 analog signal oscillators are made on FET transistors with quartz frequency stabilization. To expand the measurement range and increase accuracy in the tester, two oscillators, 2000 kHz and 3580 kHz are used. The measurement method used in the tester poses high demands on the quality of the analog signal. Filtered with quartz crystal band pass filters and amplified to the required level by a powerful operational amplifier THS3001CD.  At the output of the amplifier we have a high-quality sine, with an amplitude of up to 2 Volts and a second harmonic level harmonic level below -60dbc.

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 0.0005 °.

Due to the fact that the temperature of the elements on the board affects the measurement results, the board is equipped with a programmed temperature sensor with the ability to use in the thermostat mode in standalone mode.  The temperature of approx. 47°C is maintained at an accuracy of 0.0625°C by a fan mounted on the back of the tester.

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

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).


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.

Four-layer circuit board device developed in the program Altium Designer.

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

Assembled power supply board

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

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

The tester assembled by Accu-sembly on the printed circuit boards manufactured by NexPCB. Fine quality and excellent work. By the way quality is excellent value several times lower than in USA.

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

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%

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